RPEP-00001 · 1975The researchers identified enkephalin as consisting of two related pentapeptides (five-amino-acid chains): met-enkephalin (Tyr-Gly-Gly-Phe-Met) and leu-enkephalin (Tyr-Gly-Gly-Phe-Leu). These peptides differ only in their final amino acid — methionine versus leucine. Both act as natural ligands (binding molecules) for opioid receptors in the brain, meaning they are the body's endogenous counterparts to plant-derived opiates like morphine.
The identification was confirmed by sequencing the natural peptides using the dansyl-Edman procedure and mass spectrometry, then chemically synthesizing both sequences and showing they matched the biological activity of the natural extracts.
Hughes, J; Smith, T W; Kosterlitz, H W; Fothergill, L A; Morgan, B A; Morris, H R ·
RPEP-00002 · 1978The researchers isolated, sequenced, and synthesized the Delta Sleep-Inducing Peptide (DSIP) — a nine-amino-acid peptide (Trp-Ala-Gly-Gly-Asp-Ala-Ser-Gly-Glu) from rabbit cerebral venous blood during electrical stimulation of sleep-promoting brain regions. When the synthetic DSIP was infused into rabbit brain ventricles at 6 nmol/kg, it increased delta wave EEG activity by 35% in both the neocortex and limbic cortex compared to controls. Only the alpha-aspartyl form was active; the beta-Asp isomer was inactive. None of the 8 other tested peptides (metabolic fragments and analogs) reproduced the effect.
Schoenenberger, G A; Maier, P F; Tobler, H J; Wilson, K; Monnier, M ·
RPEP-00004 · 1980The mutant F1 ATPase (an enzyme that helps cells make energy) had only 6 to 9 units of activity per milligram of protein. That is about 10 to 15 times less than the normal version.
The mutant enzyme also broke down faster. After two weeks in the freezer at minus 80 degrees Celsius, it lost about 80% of its activity. The normal enzyme lost none.
When researchers swapped the beta subunit from a normal enzyme into the broken one, activity jumped back up to about 20 units per milligram. That confirmed the problem was in the beta subunit alone. Peptide mapping showed just one peptide fragment differed between the mutant and normal beta subunits.
Kanazawa, H; Horiuchi, Y; Takagi, M; Ishino, Y; Futai, M · In Vitro
RPEP-00006 · 1980DSIP administered systemically (40-160 nmol/kg) did not significantly reduce motor activity over 24 hours, and neither injection nor infusion of DSIP into brain ventricles (7-24 nmol) significantly increased sleep or EEG delta power. AVT injected into brain ventricles at extremely low doses (10⁻¹⁵ to 10⁻¹⁹ mol) similarly failed to enhance sleep.
However, both peptides showed biological activity: DSIP at 160 nmol/kg reduced dark-time motor activity 1-2 days after administration, and at 80 nmol/kg it paradoxically increased activity in the first 4 hours. Both DSIP and AVT reduced delta-band EEG power when administered into the third ventricle — the opposite of what a sleep-promoting substance would do. AVT's effects at femtomolar doses were notable, suggesting biological activity at concentrations far below typical peptide drug ranges.
Tobler, I; Borbély, A A ·
RPEP-00009 · 1981Thymosin peptides both increase and decrease TdT activity depending on the maturation stage, indicating they regulate multiple phases of T-cell development.
Hu, S K; Low, T L; Goldstein, A L · Animal Study
RPEP-00011 · 1981When DSIP (delta sleep-inducing peptide) was given intravenously to healthy volunteers, total sleep time increased by 59% within 130 minutes of the morning infusion compared to placebo. Subjects immediately reported a feeling of 'sleep pressure' after receiving the peptide.
DSIP also produced delayed effects on nighttime sleep: shorter time to fall asleep, reduced stage 1 (lightest) sleep, and better overall sleep efficiency. Critically, detailed behavioral and EEG analysis showed no sedation in the traditional pharmacological sense — DSIP appeared to support natural sleep mechanisms rather than forcing unconsciousness. No psychological, physiological, or biochemical side effects were observed.
Schneider-Helmert, D; Gnirss, F; Monnier, M; Schenker, J; Schoenenberger, G A · Double Blind Crossover Trial
RPEP-00014 · 1982Different patterns of foot shock in rats activated two distinct pain-suppression mechanisms: opioid and non-opioid stress analgesia. Adrenal demedullation (removing the adrenal medulla) and adrenal denervation reduced opioid stress analgesia but did not affect non-opioid stress analgesia. Reserpine, which is known to increase concentrations of adrenal medullary enkephalin-like peptides, potentiated the opioid form of stress analgesia.
These findings established that adrenal enkephalins — endogenous opioid peptides produced outside the brain — are key mediators of opioid stress-induced pain relief.
Lewis, J W; Tordoff, M G; Sherman, J E; Liebeskind, J C ·
RPEP-00017 · 1983Mice lost immune killing power as they aged. By 24 months (equivalent to roughly 70+ human years), their spleen cells were much weaker at destroying tumor cells compared to 1-month-old mice.
Four thymic hormones were tested: FTS (serum thymic factor), TP5 (a fragment of thymopoietin), TM4 (a synthetic version of TP5), and thymosin fraction V. Each worked differently depending on the age of the mouse and the dose used.
The most striking result: TM4 at a very low dose (1 nanogram) actually suppressed immune killing in young mice but significantly boosted it in 12- and 24-month-old mice. FTS and TP5 partially restored killing ability in old mice. Thymosin fraction V had modest and inconsistent effects.
Ghanta, V K; Noble, P J; Brown, M E; Cox, P J; Hiramoto, N S; Hiramoto, R N · Animal Study
RPEP-00018 · 1983Intravenous VIP caused significant bronchodilation in all seven asthmatic volunteers and protected against histamine-induced bronchoconstriction in every subject. The dose was 6 pmol/kg/min infused over 15 minutes. Side effects included tachycardia (rapid heart rate) and cutaneous flushing during the infusion.
Morice, A; Unwin, R J; Sever, P S ·
RPEP-00020 · 1984Two versions of somatostatin-28 were isolated from anglerfish tissue. Both came from the same gene, but one had a modified amino acid: 5-hydroxylysine at position 23.
Mass spectrometry confirmed the two forms had molecular weights of 3,220 (hydroxylated) and 3,204 (non-hydroxylated). The 16-unit difference matches exactly what adding one oxygen atom would do.
This was the first documented case of a hydroxylated peptide hormone. Before this, hydroxylysine was known almost exclusively from collagen (the protein that gives skin and bones their structure).
Andrews, P C; Hawke, D; Shively, J E; Dixon, J E · In Vitro
RPEP-00021 · 1984Delta-sleep-inducing peptide (DSIP) is a nonapeptide (nine amino acids, molecular weight 849) that primarily induces delta sleep (deep, slow-wave sleep) in rabbits, rats, mice, and humans, while in cats it more strongly affects REM sleep. The peptide was one of only two purified and characterized sleep-inducing peptides at the time of this review.
DSIP shows a U-shaped dose-response curve — meaning both too little and too much are less effective, with an optimal middle dose. DSIP-like material was found throughout the brain and peripheral organs via immunoassays and was detected in the blood plasma of several mammalian species. Beyond sleep, DSIP affects neurotransmitter levels, circadian rhythms, locomotor activity, hormone levels, psychological performance, and even modifies the effects of neuropharmacological drugs including withdrawal symptoms.
Graf, M V; Kastin, A J · Review
RPEP-00023 · 1984Serum procollagen type III aminoterminal peptide was elevated in 90% of patients with alcoholic hepatitis and cirrhosis, while type I carboxyterminal peptide was elevated in 60–80% of these patients. Both peptides were significantly higher in alcoholic hepatitis and cirrhosis compared to fatty liver alone (type III: p<0.001; type I: p<0.005).
However, these tests could not reliably distinguish simple fatty liver from fatty liver with early fibrosis. The highest peptide levels were found in patients with alcoholic hepatitis who also had numerous Mallory bodies, suggesting the measurements partly reflect hepatic inflammation rather than fibrosis alone.
Savolainen, E R; Goldberg, B; Leo, M A; Velez, M; Lieber, C S · Diagnostic
RPEP-00024 · 1985Natural killer (NK) cells are immune cells that destroy virus-infected and cancer cells without needing prior training. Cyclophosphamide (CY), a chemotherapy drug, wiped out NK cell activity in mice.
Interferon alone (30,000 units per mouse) strongly boosted NK cells in healthy mice. But in CY-suppressed mice, interferon by itself did nothing.
The combination worked: thymosin alpha 1 (200 micrograms/kg) given daily for 4 days, followed by a single interferon injection 24 hours before testing, fully restored NK cell activity in the immunosuppressed mice. Thymosin alpha 1 also accelerated NK cell recovery in mice that received bone marrow transplants.
Favalli, C; Jezzi, T; Mastino, A; Rinaldi-Garaci, C; Riccardi, C; Garaci, E · Animal Study
RPEP-00026 · 1985The paper argued that certain molecules made by immune cells can send signals directly to the brain. The authors named these 'immunotransmitters,' a new term for molecules that carry information from the immune system to the central nervous system (CNS).
Examples include thymosin alpha 1 and thymosin beta 4 (peptides from the thymus gland), as well as ACTH (a stress hormone), TSH (thyroid hormone), and beta-endorphin (a natural painkiller) produced by lymphocytes (white blood cells).
The review presented evidence that thymosin peptides can alter the hypothalamic-pituitary-adrenal (HPA) axis, which is the brain's master hormone control system. They also appeared to affect the gonadal (reproductive hormone) axis.
Hall, N R; McGillis, J P; Spangelo, B L; Goldstein, A L · Review
RPEP-00027 · 1985Parathymosin alpha is a newly discovered peptide of about 105 amino acid residues, isolated from rat thymus tissue. The first 30 amino acids of its sequence showed 43% structural identity with thymosin alpha 1 and prothymosin alpha.
The structural overlap did not include residues 2 through 9 of thymosin alpha 1. This explained why antibodies targeting that region of thymosin alpha 1 did not recognize parathymosin alpha.
Functionally, parathymosin alpha appeared to regulate prothymosin alpha's ability to protect sensitive mice from Candida albicans (a common fungal infection). This suggests it acts as a modulator of immune protection rather than a direct immune booster.
Haritos, A A; Salvin, S B; Blacher, R; Stein, S; Horecker, B L · In Vitro
RPEP-00029 · 1985Human small cell lung cancer (SCLC) cells express high-affinity receptors for bombesin/GRP (gastrin-releasing peptide) — with about 2,000 binding sites per cell and a binding affinity (Kd) of 0.5 nM. The receptor binding was specific: bombesin and the structurally related peptide GRP competed for binding, but unrelated peptides like substance P and vasopressin did not.
Critically, since SCLC cells both produce bombesin/GRP-like peptides AND express receptors for them, these peptides likely function as autocrine growth factors — the cancer cells stimulate their own growth through a self-reinforcing peptide signaling loop. The receptor was identified as a 78,000-dalton (78 kDa) polypeptide.
Moody, T W; Carney, D N; Cuttitta, F; Quattrocchi, K; Minna, J D · In Vitro
RPEP-00031 · 1985The patient had primary intestinal lymphangiectasia (a condition where lymph vessels in the gut leak fluid, protein, and immune cells). Biopsies confirmed the diagnosis in her intestines, lungs, and lymph nodes. Lymphocytes were literally leaking out through her gut, confirmed by finding them in her stool.
Her thymus gland was essentially absent. A biopsy showed no thymic tissue. Blood tests showed very low or absent thymulin and thymosin alpha 1. She had a selective loss of T-cells, especially CD4+ helper T-cells.
Daily thymosin fraction 5 treatment produced a brief clinical improvement. But switching to weekly injections could not sustain it. Lymphocyte numbers never increased during treatment. The authors concluded that when the body loses T-cells faster than it can replace them, even thymic hormones cannot keep up without a functioning thymus.
Sorensen, R U; Halpin, T C; Abramowsky, C R; Hornick, D L; Miller, K M; Naylor, P; Incefy, G S · Case Report
RPEP-00032 · 1985Normal thymosin alpha 1 levels were similar across all groups of women tested, regardless of their hormonal status. This peptide appears unaffected by estrogen.
Thymosin beta 4 told a different story. Castrated women not receiving estrogen had reduced levels. Postmenopausal women on chronic estrogen therapy had even lower thymosin beta 4. Castrated women on estrogen also showed decreased levels.
Normal women in the early follicular phase (low estrogen point of the menstrual cycle), women with premature ovarian failure, and postmenopausal women not on estrogen all had similar thymosin beta 4 levels. But the premature ovarian failure and postmenopausal groups showed wide variation, suggesting these are not uniform populations.
Suh, B Y; Naylor, P H; Goldstein, A L; Rebar, R W · Cross Sectional
RPEP-00033 · 1985Thymosin alpha 1 (Ta-1) had strikingly different effects depending on the mouse strain. In B10.D2 mice (resistant to autoimmune thyroiditis), Ta-1 treatment between the two antigen injections actually increased thyroid inflammation. In B10.Br mice (naturally susceptible), Ta-1 suppressed the disease.
Timing mattered. Early treatment (first 2 weeks) suppressed disease in the susceptible strain but worsened it in the resistant strain. Later treatment (weeks 3-4) had similar patterns.
Different doses affected different T-cell subsets. The 0.01 microgram dose lowered Lyt-2+3+ cells (a type of immune cell) in resistant mice. The 0.001 microgram dose raised Lyt-1+ cells in the same strain. Each dose shifted the immune balance differently, which explains the opposing disease outcomes.
Tomazic, V J; Novotny, E A; Ordonez, J V · Animal Study
RPEP-00034 · 1985Leukocyte migration inhibition (LMI), a measure of how well immune cells respond to signals, was impaired in 24 head and neck cancer patients compared to healthy people.
Adding thymosin alpha 1 to the lab dish improved LMI in the cancer patients' cells. The improvement appeared independent of T-cell subset levels, meaning thymosin alpha 1 was enhancing the function of existing cells rather than changing which cells were present.
An interesting secondary finding: patients whose LMI was still normal had lower levels of suppressor/cytotoxic T-cells than both healthy people and patients with impaired LMI. This suggests that suppressor cells may contribute to the immune dysfunction in these cancers.
Wolf, G T; Peterson, K A; Lovett, E J · In Vitro
RPEP-00036 · 1986Normal thymosin alpha 1 levels: 670 ± 163 pg/mL for males and 652 ± 162 pg/mL for females. Normal thymosin beta 4 levels: 974 ± 400 ng/mL for males and 889 ± 345 ng/mL for females. Note that beta 4 levels are about 1,000 times higher than alpha 1.
In AIDS patients, 57% had elevated thymosin alpha 1 and 48% had elevated thymosin beta 4. But there was no correlation between the two peptides' levels in any group, including healthy controls.
People with AIDS-related immune dysfunction (not full AIDS) showed a different pattern: 54% had elevated thymosin alpha 1 but only 15% had elevated thymosin beta 4. This suggests thymosin alpha 1 rises earlier in the disease process.
Naylor, P H; Friedman-Kien, A; Hersh, E; Erdos, M; Goldstein, A L · Cross Sectional
RPEP-00037 · 1986Thymosin fraction 5 (TF5), a mix of thymic peptides, significantly increased both the percentage of human lymphocytes expressing IL-2 receptors (IL-2R) and the density of receptors on each cell. This happened after the cells were stimulated with PHA (a plant protein that activates immune cells).
Synthetic thymosin alpha 1 alone produced the same effect, identifying it as the active ingredient in TF5.
The effect was direct. When researchers used cyclosporin A (a drug that blocks IL-2 production), TF5 still increased IL-2R expression. This means thymosin works by directly putting more receptors on cells, not by making more IL-2. More receptors led to stronger cell multiplication.
Sztein, M B; Serrate, S A; Goldstein, A L · In Vitro
RPEP-00038 · 1986Serum amino-terminal type III procollagen peptide levels showed a strong positive correlation with the degree of liver fibrosis (r = 0.733, p < 0.001) in patients with alcoholic liver disease. In contrast, serum proline levels and standard liver function tests failed to correlate significantly with the actual extent of fibrotic tissue measured by morphometric analysis of liver biopsies.
Tanaka, Y; Minato, Y; Hasumura, Y; Takeuchi, J ·
RPEP-00040 · 1987Using a "pan-opioid" antibody that detects all opioid peptides, researchers screened 108 tumors. Every adrenal pheochromocytoma (15 of 15), thyroid medullary carcinoma (6 of 6), and pituitary adenoma (5 of 5) stained positive for opioid peptides.
Most parathyroid adenomas (8 of 9), pancreatic islet-cell tumors (7 of 10), and carcinoid tumors (18 of 26) also stained positive.
Zero non-neuroendocrine tumors showed opioid staining. Lung small-cell carcinomas, skin Merkel-cell tumors, and neuroblastomas were all negative.
The same opioid peptides were found in normal versions of these tissues (adrenal medulla, pancreatic islets, pituitary), suggesting the tumors simply overproduce a normal cellular product.
Bostwick, D G; Null, W E; Holmes, D; Weber, E; Barchas, J D; Bensch, K G · Cross Sectional
RPEP-00042 · 1987Serum levels of the N-terminal procollagen type III peptide (PIIINP) showed a high correlation with the degree of liver fibrosis in patients with schistosomiasis. This peptide biomarker tracked with histopathological findings from liver biopsies, suggesting it could serve as a non-invasive marker to monitor the dynamic process of liver scarring — something a one-time biopsy cannot capture.
el-Mohandes, M; Hassanein, H; el-Badrawy, N; Voss, B; Gerlach, U · Observational
RPEP-00043 · 1987IL-2 is a 133-amino acid protein (molecular weight 15,420 daltons) produced by activated T-cells. Its gene sits on chromosome 4. The IL-2 receptor is a 272-amino acid protein (55,000 daltons).
IL-2 does not just make immune cells copy themselves. It moves cells from a resting state (G1) through to DNA synthesis (S phase). During this process, the proto-oncogene c-myb increases 6 to 7 times above normal levels.
The most exciting clinical development: IL-2 could expand LAK cells (lymphokine-activated killer cells) and TIL (tumor-infiltrating lymphocytes) that attack cancer. Early human trials showed both therapeutic promise and significant toxicity.
Thymosin fraction 5 and thymosin alpha 1 could modulate IL-2 receptor expression on human blood cells, potentially increasing the effectiveness of IL-2 therapy.
Fletcher, M; Goldstein, A L · Review
RPEP-00045 · 1987A single injection of kainic acid (1 microgram) into rat brains caused seizures lasting 3 to 6 hours. During seizures, hippocampal met-enkephalin dropped 31% and dynorphin A dropped 63%, suggesting these opioid peptides were being released.
By 24 hours, levels returned to normal. By 48 hours, met-enkephalin surged to 270% of normal and dynorphin to 150%. The brain had ramped up production to replace what was used.
The biosynthetic machinery confirmed this: mRNA for preproenkephalin (the genetic template for making enkephalin) jumped to 400% of control at 6 hours. The actual precursor protein followed at 24 hours, reaching 300% of control.
The seizure-induced shaking behavior (wet-dog shakes) was directly linked to enkephalin. Naloxone (an opioid blocker) reduced the shaking. Anti-enkephalin antibodies also reduced it. Injecting enkephalin peptides into the hippocampus mimicked the shaking.
Hong, J S; Grimes, L; Kanamatsu, T; McGinty, J F · Animal Study
RPEP-00046 · 1987All four tested opioid peptides (beta-endorphin, dynorphin, MEAP, and DADLE) increased plasma corticosterone (a stress hormone) in normal rats. The effects were dose-dependent and blocked by naloxone, confirming they work through opioid receptors.
Cross-tolerance experiments revealed which receptor each peptide uses. Rats made tolerant to one opioid were tested with others. Dynorphin(1-13) and MEAP (Met-Enk-Arg-Phe) acted at kappa-opioid receptors. The synthetic peptide DADLE acted at delta-opioid receptors.
Beta-endorphin was the surprise. It did not fit neatly into the mu, delta, or kappa categories. Its corticosterone-releasing effect was maintained even in rats tolerant to all three receptor types. The researchers proposed it acts at an epsilon-opioid receptor, a debated fourth receptor type.
Iyengar, S; Kim, H S; Wood, P L · Animal Study
RPEP-00048 · 1987The percentage of E-rosettes (a marker of mature T-cells) was lower in 33 acutely malnourished children compared to mildly growth-retarded children from the same area. But there was considerable overlap between groups, meaning not every malnourished child had low T-cells.
This differed from studies in other countries where all severely malnourished children showed uniformly depressed T-cell markers. The authors suggested that specific nutrient deficiencies, not malnutrition overall, may drive immune problems.
Adding thymosin fraction 5 to the children's blood cells in lab dishes increased E-rosette formation in a dose-dependent manner. This means immature T-cell precursors were present in the blood and could be pushed toward maturity with thymic peptides.
Keusch, G T; Cruz, J R; Torun, B; Urrutia, J J; Smith, H; Goldstein, A L · Cross Sectional
RPEP-00049 · 1987Beta-endorphin (0.5 microgram injected into the brain), dynorphin (1 microgram), and U50-488H (a kappa opioid drug, 10 mg/kg) all stimulated prolactin (PRL) release more in the afternoon (4-5 PM) than in the morning (8-9 AM).
Morphine (10 mg/kg subcutaneous), met-enkephalin (200 micrograms), and D-Met-Pro-Enk (0.5 microgram) did not show this daily rhythm. Their prolactin response was the same regardless of time.
For corticosterone (a stress hormone), the pattern was different. Morphine, D-Met-Pro-Enk, met-enkephalin, and dynorphin could only increase corticosterone in the morning, when baseline levels were low. In the afternoon, when baseline corticosterone was already high, there was no room for further increase.
Removing the adrenal glands eliminated the circadian rhythm in prolactin responses, suggesting that natural cortisol cycling drives the time-of-day differences.
Kiem, D T; Kanyicska, B; Stark, E; Fekete, M I · Animal Study
RPEP-00050 · 1987Rats drinking 2% salt solution showed progressive increases in three neuropeptide mRNAs in the hypothalamus (a brain region controlling hormones):
Vasopressin, oxytocin, and dynorphin mRNAs all increased in the magnocellular neurons of the supraoptic and paraventricular nuclei. These are the brain cells that make these peptide hormones.
Enkephalin mRNA was not detectable in these brain areas under normal conditions. It only appeared after 12 days of salt loading or after the acute stress of a salt injection into the abdomen.
Lactating mother rats (10 days postpartum) showed a very large increase in oxytocin mRNA, with smaller increases in vasopressin and dynorphin. No enkephalin or CRF (corticotrophin-releasing factor) changes were seen in lactating rats.
Lightman, S L; Young, W S · Animal Study
RPEP-00051 · 1987Severe brain injury (3.0 to 4.0 atmospheres of pressure) caused dynorphin to increase significantly in five brain regions: striatum, frontal cortex, parietal cortex, pons, and medulla. These were the same regions with the worst tissue damage.
Beta-endorphin decreased in the hypothalamus after severe injury but increased in the anterior pituitary after both mild and severe trauma. Enkephalin levels did not change at any injury level.
The dynorphin increase in the medulla was significantly correlated with falling mean arterial blood pressure after severe injury. This suggests dynorphin release may contribute to the cardiovascular collapse that worsens outcomes after head trauma.
McIntosh, T K; Head, V A; Faden, A I · Animal Study
RPEP-00052 · 1987Dynorphin A accumulated in injured brain regions after fluid-percussion brain injury in cats. These same regions showed significant decreases in cerebral blood flow. Enkephalin did not accumulate.
The opioid antagonist Win-(-), given 15 minutes after injury, significantly improved multiple outcomes: mean arterial blood pressure increased, EEG amplitude (brain wave activity) improved, regional cerebral blood flow recovered, and both the severity and incidence of brain hemorrhage decreased. Survival after injury was significantly better.
The control was elegant: Win-(+), the mirror-image version of the same drug that cannot bind opioid receptors, had no effect. Neither did saline. This confirmed the benefits came specifically from blocking opioid receptors.
McIntosh, T K; Hayes, R L; DeWitt, D S; Agura, V; Faden, A I · Animal Study
RPEP-00053 · 1987Electrical stimulation of the periaqueductal grey (PAG, a brain region that controls pain) initially produced strong pain relief in rats. With repeated stimulation, this relief gradually disappeared.
The tolerance was not from opioid depletion. Brain levels of beta-endorphin, met-enkephalin, and dynorphin were unchanged in tolerant rats compared to controls.
It was not a learned (conditioned) response either. Tolerant rats exposed to all the cues associated with stimulation showed no compensatory pain increase. And repeated exposure to the cues without stimulation did not restore pain relief.
The tolerance behaved exactly like drug tolerance: the dose-response curve shifted right (needed more stimulation for the same effect), it was reversed by naloxone, and it recovered spontaneously over time. Tolerant rats also showed cross-tolerance to morphine, confirming the same opioid receptor system was involved.
Rats showed no signs of stress during the protocol: normal body weight, food intake, temperature, adrenal weight, and hormone levels.
Millan, M J; Członkowski, A; Herz, A · Animal Study
RPEP-00054 · 1987Human cerebrospinal fluid (CSF) from pain-free surgery patients contained Peak B at a concentration equivalent to about 1.4 picomoles of morphine per milliliter.
Injected into mouse brains, Peak B produced dose-dependent pain relief at 0.06 and 0.12 picomoles of morphine equivalents. Naloxone (an opioid blocker) reversed this effect, confirming it works through opioid receptors.
In a muscle tissue assay (mouse vas deferens), Peak B's activity was blocked by low naloxone concentrations but not high ones. This unusual pattern suggests it interacts with opioid receptors differently than known opioids.
Most surprisingly, Peak B was not destroyed by trypsin or alpha-chymotrypsin, protein-digesting enzymes that break down all known opioid peptides. This means Peak B is either not a peptide or has an unusual structure that protects it from enzymes.
Miller, B E; Lipman, J J; Byrne, W L · In Vitro
RPEP-00055 · 1987Delta sleep-inducing peptide (DSIP) administered intravenously at 25 nmol/kg over four nights showed some improvements in sleep metrics in chronic insomniacs — including reduced awakenings, decreased waking time, and increased total sleep time — but these changes were not statistically significant compared to placebo. The only significant increases were in NREM sleep time and stage 2 sleep, but these differences already existed at baseline, undermining the finding. The authors concluded that DSIP's sleep-improving effects are of little clinical significance.
Monti, J M; Debellis, J; Alterwain, P; Pellejero, T; Monti, D · Randomized Controlled Trial
RPEP-00056 · 1987The new enzyme immunoassay (EIA) for thymulin achieved a sensitivity of 32.5 ± 5 pg/mL (IC50) with a detection limit of 5 pg/mL. This was more sensitive than previously available radioimmunoassays.
The test was highly specific. It did not cross-react with thymosin alpha 1, thymopoietin II, or TP5 (another thymic peptide). Both the zinc-bound (biologically active) and zinc-free forms of thymulin showed the same immunoreactivity.
Mapping studies showed that the minimum peptide structure needed for detection was the C-terminal portion from lysine-3 to asparagine-9 (7 of the 9 amino acids).
Métreau, E; Pléau, J M; Dardenne, M; Bach, J F; Pradelles, P · In Vitro
RPEP-00057 · 1987Eight monoclonal antibodies against thymosin alpha 1 were produced from mice immunized with synthetic thymosin alpha 1. The antibodies were screened using both solid-phase ELISA and liquid-phase radioimmunoassay for maximum specificity.
Using indirect immunofluorescence on perfused rat thymus tissue, thymosin alpha 1-containing cells were found primarily in the thymic medulla. This confirmed earlier studies that used less specific polyclonal antibodies.
The monoclonal antibodies provide a standardized, unlimited supply of reagent compared to the variable polyclonal antisera used previously. They can be used for both in vitro and in vivo studies of thymosin alpha 1 location and function.
Oates, K K; Naylor, P H; Goldstein, A L · In Vitro
RPEP-00059 · 1987Peripheral mu-opioid receptors in the gut can independently slow gastrointestinal transit. The peptide agonist PL017 slowed gut transit at 0.37 mg/kg but did not produce pain relief until 30 mg/kg, about 80 times higher. This proves gut mu receptors work independently of brain receptors.
Delta and kappa opioid receptors in the gut also slowed transit, but less powerfully than mu receptors.
The key finding: a peptide opioid antagonist that cannot cross the blood-brain barrier blocked morphine's gut-slowing effect without reducing its painkilling activity. This pharmacological separation means constipation and pain relief work through different receptor populations (gut vs brain).
Shook, J E; Pelton, J T; Hruby, V J; Burks, T F · Animal Study
RPEP-00060 · 1987Thymosin alpha-1 and lymphokine-containing supernatants directly stimulated both basal and corticotropin-induced corticosterone secretion from adrenal cells.
Torres-Alemán, I; Rejas, M T; Barasoaín, I; Borrell, J; Guaza, C · In Vitro
RPEP-00061 · 1987The new method combined HPLC (high-performance liquid chromatography) with radioimmunoassay (RIA) to measure opioid peptides in human cerebrospinal fluid, plasma, and tissues.
The key advantage: HPLC first separates beta-endorphin from its precursor beta-lipotropin and from other opioid peptides. Then RIA measures each fraction individually. This eliminates cross-reactivity, where antibodies confuse one peptide for another.
The method uses volatile solvents that evaporate cleanly without interfering with the antibody tests. This was the first combined method that could accurately measure endorphin, enkephalin, and dynorphin families in the same sample.
Preliminary results from chronic pain patients' CSF were presented, demonstrating the method's practical utility.
Venn, R F · In Vitro
RPEP-00063 · 1987Two closely related 23-amino-acid peptides called magainins were isolated from the skin of the African clawed frog (Xenopus laevis). These peptides kill numerous species of bacteria and fungi at low concentrations, lyse protozoa through osmotic disruption, and are water-soluble and nonhemolytic — meaning they destroy microbes without damaging red blood cells.
Both peptides derive from a common precursor protein, as confirmed by partial cDNA sequencing. They differ by only two amino acid substitutions and are potentially amphiphilic (having both water-loving and fat-loving regions), which likely explains how they interact with microbial membranes.
Zasloff, M · Laboratory Study
RPEP-00064 · 1988After middle cerebral artery occlusion (a stroke model) in rats, the opioid antagonist WIN at doses of 0.4 to 400 micrograms/kg produced several benefits.
All WIN doses significantly increased mean arterial blood pressure compared to saline controls. At the optimal dose of 40 micrograms/kg, rats showed significantly greater EEG (brain wave) recovery and higher neurological scores at 24 hours compared to controls.
Neurological outcome correlated with brain wave recovery on the injured side, confirming the measures tracked together.
However, 24-hour mortality and infarct (dead tissue) size were not significantly different from controls. The drug improved functional recovery without reducing the actual area of brain death.
At 1 hour after stroke, there were no significant changes in dynorphin, enkephalin, or endorphin levels in the injured vs. uninjured brain hemisphere. This was unexpected given the changes seen in trauma models.
Andrews, B T; McIntosh, T K; Gonzales, M F; Weinstein, P R; Faden, A I · Animal Study
RPEP-00065 · 1988Beta-endorphin was 49% higher in the pituitary of hypertensive rats (SHR) but dramatically lower in peripheral organs: 92% lower in heart, 48% lower in adrenals, and 57% lower in kidneys compared to normal rats (WKY). In the brain, beta-endorphin was 71% lower in the striatum of SHR rats.
Dynorphin was 38% lower in the pituitary, 55% lower in the striatum, and 46% lower in the heart of SHR rats, but 33% higher in the hypothalamus.
Met-enkephalin showed the opposite pattern in some areas: 268% higher in adrenals, 40% higher in cortex, and 33% higher in pons/medulla of SHR rats, but 40% lower in the pituitary.
The changes were not uniform. Each opioid peptide had its own distinct pattern of increases and decreases across brain regions and organs.
Bhargava, H N; Matwyshyn, G A; Hanissian, S; Tejwani, G A · Animal Study
RPEP-00066 · 1988Enterochromaffin (EC) cells are the most abundant hormone-producing cells in the gut. They were known to make serotonin. Whether they also make peptides was debated for years.
Using antibodies against all three families of opioid peptide precursors, researchers tested gut tissue from dogs, guinea pigs, and humans. EC cells contained pro-dynorphin-derived peptides: dynorphin A and alpha-neo-endorphin.
They did not contain pro-opiomelanocortin derivatives (like endorphin) or pro-enkephalin derivatives. Previous reports of enkephalin in EC cells were likely due to antibody cross-reactivity.
The number and staining characteristics of opioid-positive EC cells varied considerably between species and between different segments of the gut, suggesting species-specific processing of the dynorphin precursor.
Cetin, Y · In Vitro
RPEP-00067 · 1988The myenteric plexus (the nerve network that controls gut movement) of guinea pig small intestine contained a well-defined mix of opioid peptides.
Met-enkephalin dominated at 405 pmol/g of tissue. Three other enkephalin-related peptides were present at 90 to 100 pmol/g each. Two rarer enkephalin forms (BAM-18 and Met-enkephalyl-Arg-Arg-Val-NH2) were present at 24 and 5 pmol/g.
Dynorphin-family peptides (alpha-neoendorphin, beta-neoendorphin, dynorphin A(1-8), and dynorphin B) were all present at 12 to 15 pmol/g. Full-length dynorphin A was very scarce at only 0.8 pmol/g.
No beta-endorphin was detected.
The two rare enkephalin forms (BAM-18 and MERV-NH2) had an unusual receptor profile: they preferred mu and kappa opioid receptors rather than the delta receptors that most enkephalins favor. This means they may have different functional roles in the gut.
Corbett, A D; McKnight, A T; Kosterlitz, H W · In Vitro
RPEP-00068 · 1988Morphine injected into the brain (intracerebroventricular) was 10 times more potent than intravenous morphine at increasing plasma ANP (atrial natriuretic peptide), a hormone released by the heart that lowers blood pressure and promotes sodium excretion.
Leu-enkephalin decreased plasma ANP concentrations, the opposite effect of morphine.
Dynorphin and beta-endorphin (given either into the brain or into the vein) did not change ANP levels at all.
All four opioids increased plasma norepinephrine and epinephrine (stress hormones), but morphine caused increases 10 to 50 times greater than the others.
Ganglionic blockade (cutting the nerve connection from the brain to the heart) significantly reduced morphine's ability to increase ANP, confirming the effect requires an intact autonomic nervous system.
Crum, R L; Brown, M R · Animal Study
RPEP-00070 · 1988The three families of opioid peptides (dynorphins, endorphins, and enkephalins) all have cardiovascular effects. Dynorphins prefer kappa receptors, enkephalins prefer delta and mu receptors, and beta-endorphin prefers mu and delta receptors.
The review focused on mu-opioid receptors in the hypothalamus, a brain region that controls many body functions including blood pressure. While the opioid system's role in normal blood pressure regulation was not well understood, cardiovascular stress clearly activates the opioid system.
The review covered both normal cardiovascular regulation and pathological states like hypertension, hemorrhagic shock, and heart failure, where opioid system changes had been documented.
Feuerstein, G; Sirén, A L · Review
RPEP-00071 · 1988Morphine and other mu-opioid agonists decreased gastric acid secretion. They were more potent when injected into the brain (i.c.v.) than into the blood (i.v.), indicating a central mechanism.
The quaternary opioid antagonist naltrexone methylbromide (which cannot cross the blood-brain barrier) blocked brain-injected morphine's effect and partially blocked IV morphine's effect. This confirmed morphine reduces acid through brain receptors, even when given intravenously.
The kappa-selective agonist U-50,488H had the opposite effect: it increased gastric acid when given IV but not when given into the brain. This increase was blocked by naloxone, the muscarinic blocker atropine, and the M1-selective blocker pirenzepine.
The delta-selective agonist DPDPE did not affect acid secretion by either route.
Fox, D A; Burks, T F · Animal Study
RPEP-00072 · 1988Human placental aminopeptidase M completely degraded Met-enkephalin and Leu-enkephalin into their five constituent amino acids. The degradation rate was measured by tracking tyrosine release.
The degradation speed ranked: Met-enkephalin (fastest) > Leu-enkephalin > beta-neoendorphin > dynorphin > beta-endorphin (slowest).
Smaller, simpler peptides were degraded faster than larger, more complex ones. Met-enkephalin (5 amino acids) was destroyed faster than beta-endorphin (31 amino acids).
Furuhashi, M; Mizutani, S; Kurauchi, O; Kasugai, M; Narita, O; Tomoda, Y · In Vitro