Opioid Peptide Content Research Articles

Optimization Of Medical and Environmental Services Using TES Therapy

Experimental studies have shown the presence of antihypoxic, decongestant and immunomodulatory effects of endogenous opioid peptides (OP), as well as their effect on the synthesis of pituitary hormones, these effects are largely due to an increase in the blood content of opioid peptides ((3-endorphin and met-enkephalin), which are released when the structures of the antinociceptive system are activated. Studying the effect of TES therapy on reparative processes in patients with myocardial infarction and establishing that this accelerates the formation of postinfarction scar and the development of compensatory hypertrophy of extrainfarction parts of the myocardium, increases the number of cases of heart failure and the number of relapses of anginal pain, improves the general state of hemodynamics. However, until now, the question of the possibility of using TES therapy to correct the imbalance of cytokines in the acute period of myocardial infarction, which is an important pathophysiological factor in the development and course of acute cardiac pathology, remains open.

Early in Life Bladder Inflammation Alters Opioid Peptide Content in the Spinal Cord and Bladder of Adult Female Rats

Previous research suggests that a failure of opioid inhibition may contribute to chronic bladder pain. We determined how acute adult and/or prior early in life exposure to bladder inflammation alters the adult content of endogenous opioid peptides in the bladder, spinal cord and blood. Inflammation was induced by intravesical administration of zymosan. Female Sprague-Dawley® rats were exposed to anesthesia only or zymosan early in life (postnatal days 14 to 16) and anesthesia only or zymosan as adults (ages 12 to 17 weeks). Thoracolumbar and lumbosacral segments of the spinal cord, and blood and bladders were collected 24 hours after adult treatment. Opioid peptide content was measured using enzyme-linked immunosorbent assay. Early in life bladder inflammation alone produced a chronic increase in dynorphin A (1-17) in the lumbosacral spinal cord. When early in life inflammation was followed by adult re-inflammation, spinal cord dynorphin remained unchanged but bladder dynorphin was decreased. In addition, early in life inflammation combined with adult bladder inflammation decreased endomorphin-2 content in the thoracolumbar spinal cord. Neither early in life nor adult bladder inflammation affected thoracolumbar dynorphin, serum dynorphin, lumbosacral endomorphin-2 or plasma β-endorphin. Several opioid peptides were measured using enzyme-linked immunosorbent assay following early in life and adult bladder inflammation. The changes observed are consistent with the view that early in life bladder inflammation alone can chronically alter spinal cord peptide content. When coupled with adult re-inflammation, these changes could set the neurochemical stage to support bladder hypersensitivity.

Ice Water Testing Reveals Hypersensitivity in Adult Rats That Experienced Neonatal Bladder Inflammation: Implications for Painful Bladder Syndrome/Interstitial Cystitis

We determined whether clinical observations of hypersensitivity to ice water testing, that is infusion of ice-cold saline into the bladder, in patients with painful bladder syndrome/interstitial cystitis have a parallel in a rat model of bladder hypersensitivity produced by neonatal inflammation. Rat pups were anesthetized as neonates (postnatal days 14 to 16). In some pups the bladder was inflamed by intravesical zymosan treatment. As adults, the rats were re-anesthetized and tested for abdominal muscle contractions to ice water testing, measured on electromyogram. Various neonatally treated groups of rats underwent bladder re-inflammation/no re-inflammation and/or bladder distention before ice water testing. Other control rats were treated only in adulthood. Rats that underwent bladder inflammation as neonates manifested bladder hypersensitivity in adulthood, as indexed by significantly greater mean electromyogram responses during ice water testing. This bladder hypersensitivity did not require adult re-inflammation to manifest. Hypersensitivity was also observed with or without prior bladder distention, although the magnitude of electromyogram responses during ice water testing significantly correlated with the magnitude of electromyogram responses to bladder distention. Neonatally induced effects were not significantly related to estrous cycle phase. Exposure to menthol did not significantly enhance the overall magnitude of the electromyogram response to ice water testing in neonatally treated rats. Current results parallel those in a recent study showing that most patients with painful bladder syndrome/interstitial cystitis experience pain when undergoing ice water testing after previous urodynamic testing. These findings suggest that this animal model may be useful for understanding the etiology of and treatment for painful bladder syndrome/interstitial cystitis.

Striatal opioid peptide content in an animal model of spontaneous stereotypic behavior

Stereotypic behaviors are associated with a broad spectrum of developmental, psychiatric, and genetic disorders. Several lines of evidence indicate that these abnormal repetitive behaviors may be expressed as a consequence of imbalanced activity along the direct and indirect processing pathways of the basal ganglia. Because the activity of these two pathways is modulated, in part, by the neuropeptides dynorphin and enkephalin, we sought to determine whether spontaneous and persistent stereotypy is associated with alterations in striatal neuropeptide content. Specifically, the present study employed radioimmunoassay to measure dynorphin-A and leu-enkephalin content in the dorsolateral striatum of deer mice exhibiting different levels of spontaneous stereotypic jumping. The results indicate significantly decreased leu-enkephalin content and significantly increased dynorphin/enkephalin content ratios in high-stereotypy mice relative to low-stereotypy mice. Moreover, analyses revealed a significant negative correlation between striatal enkephalin content and frequency of stereotypy as well as a significant positive correlation between the dynorphin/enkephalin content ratio and frequency of stereotypy in these mice. These data are consistent with the hypothesis that spontaneous stereotypic behavior is expressed as a consequence of relative hyperactivity along cortico-basal ganglia-cortical feedback circuits involving the direct (facilitative) pathway, but suggest that primary perturbations to the indirect (inhibitory) pathway give rise to such imbalanced activity.

Mobilization of Opioid-containing Polymorphonuclear Cells by Hematopoietic Growth Factors and Influence on Inflammatory Pain

Leukocytes can control inflammatory pain by secretion of opioid peptides, stimulated by cold-water swimming or local injection of corticotropin-releasing factor, and subsequent activation of opioid receptors on peripheral sensory neurons. This study investigated whether mobilization of polymorphonuclear cells (PMN) by granulocyte colony-stimulating factor (G-CSF) and stem cell factor (SCF) enhances immigration of opioid-containing PMN and peripheral opioid analgesia in rats with Freund complete adjuvant-induced hind paw inflammation. In circulating PMN of rats treated with G-CSF+SCF and sham-treated rats, opioid peptide content was measured by radioimmunoassay. Expression of adhesion molecules (CD62L, CD49d, CD18), in vitro migration in the Boyden chamber, and infiltrating leukocytes were analyzed by flow cytometry. Chemokine messenger RNA transcription was quantified by LightCycler polymerase chain reaction. Paw pressure threshold was measured at baseline, after cold-water swimming, and after injection of corticotropin-releasing factor. G-CSF+SCF treatment increased circulating PMN (11-fold, P < 0.05). Mobilized PMN had decreased content of beta-endorphin but not of Met-enkephalin per cell, down-regulation of CD62L, up-regulation of CD49d (but no change in CD18), and reduced migration toward higher chemokine concentrations (all P < 0.05). In the paw, one of four chemokine messenger RNAs was significantly expressed during the first 2 h of inflammation (P < 0.05), immigration of PMN and opioid-containing cells was slightly increased (1.5-fold, P < 0.05), and baseline paw pressure threshold, as well as paw pressure threshold increases induced by corticotropin-releasing factor and cold-water swimming, were unchanged (P > 0.05). G-CSF+SCF mobilized circulating opioid-containing PMN but had a minor influence on cell migration and peripheral analgesia, probably because of the low expression of chemokines in the inflamed paw and one of the decreased beta-endorphin content in PMN.

Role of endogenous opioid peptides in protection of ischemic preconditioning in rat small intestine

This study investigated the protective effects of ischemic preconditioning on intestinal ischemic injury and the role of endogenous opioid peptides (EOP) in these effects. Ischemia-reperfusion (I/R) induced by 30-min of ischemia and 60-min of reperfusion significantly increased the levels of malondialdehyde (MDA) and lactate dehydrogenase (LDH) and resulted in serious intestinal edema (wet weight/dry weight). The ischemic preconditioning (PC) elicited by three 8-min occlusion periods interspersed with 10-min reperfusion markedly attenuated intestinal injury caused by ischemia-reperfusion. Pretreatment with morphine (300μg·kg −1, iv) 10-min before ischemia and reperfusion mimicked the protection produced by PC. Naloxone (3mg·kg −1, iv) abolished the protection of morphine-induced preconditioning and ischemic preconditioning in rat intestine. However, there were no changes between naloxone alone and control groups. Treatment with naloxone before ischemia-reperfusion had no effect on animals compared with the I/R group. In addition, we also measured the content of endogenous opioid peptides (Leu-enkephalin) in the effluent which was collected before and during preconditioning. It was shown that the release of leu-enkephalin was markedly increased during preconditioning. These results suggested that EOP might play an important role in PC in rat small intestine.

Gender differences in opioid-mediated analgesia: animal and human studies.

Gender differences in opioid-mediated analgesia: animal and human studies.

Amygdala kindling modifies extracellular opioid peptide content in rat hippocampus measured by microdialysis.

Opioid peptide release in the hippocampus was shown to be increased immediately following amygdala kindling stimulation in freely moving rats using microdialysis combined with a universal opioid peptide radioimmunoassay (RIA). Extracellular opioid peptide levels were elevated (55% above basal levels) within the first 10 min after electrical stimulation-induced partial seizures in previously nonkindled animals. Fully kindled rats showed lower extracellular opioid peptide levels (40% reduction) during the interictal period [16 +/- 2.1 days (mean +/- SEM) after the last stage V seizure], in comparison with values obtained from the sham-kindled group under basal conditions. However, opioid peptide release in fully kindled rats increased above 152% of interictal levels within the first 20 min after onset of fully kindled seizures, attaining peak levels equal to that of the partial kindled group and returning to prestimulation conditions 40-60 min following the ictal events. The majority of the immunoreactive material recovered from the hippocampus within the first 20 min following partial and generalized kindled seizures coeluted with dynorphin-A (1-6), dynorphin-A (1-8), and Leu-enkephalin by HPLC/RIA analysis. It is proposed that the enhanced opioid peptide release in hippocampus induced by amygdala kindling stimulation might be associated with either enhanced excitability or seizure suppression as seizure susceptibility fluctuates. The reduced interictal opioid peptide levels may also underlie some interictal behavioral disturbances.

Opioid peptides content in the rat brain during the ictal phase and after pentylenetetrazol-kindled rats

We determine the opioid peptide content in the rat brain during the ictal phase and postictal depression after pentylenetetrazol kindling rats. Radioimmunoassays with highly specific antisera risen for Met-enkephalin, Leu-enkephalin and octapeptide, were carried out during the ictal phase, and 15, 30 and 60 min after seizures. We always found an initial IR-Met-enkephalin decrease during the postictal depression content, followed by a reduction in IR-Leu-enkephalin and IR-octapeptide tissular concentration. We suggest a functional and differential release of the opioid peptides, during the postictal depression time-course.

Hypothalamic corticotropin-releasing hormone and opioid peptide neurons: functional changes after adrenalectomy and/or castration.

The influences of short- and long-term castration and adrenalectomy (or both) upon corticotropin-releasing hormone (CRH) mRNA levels, CRH peptide levels, and endogenous opioid peptide (EOP) content in the hypothalamus, and basal and CRH-stimulated EOP release in vitro, were examined. Gonadal and adrenal steroids regulated the function of these hypothalamic peptidergic systems in terms of peptide synthesis, storage pools, and secretion. The steroids were also found to alter the sensitivity of EOPergic neurons to CRH. In some cases, evidence was obtained for an interaction between gonadal and adrenal steroids in determining neuronal function (seen as additive or counteractive effects). A finding of major importance was that the response of these peptidergic systems was markedly influenced by the duration of steroid deprivation, the results of chronic treatment often being opposite to those of acute treatment. Lastly, inspection of the data on peptide synthesis, storage and release, revealed that there was no simple relationship between these three parameters even within a single type of peptidergic neuron.

Regulation of Proenkephalin Synthesis in Adrenal Medullary Chromaffin Cells

The synthesis of proenkephalin was assessed in primary cultures of bovine adrenal medullary chromaffin cells by incubation of the cells with [35S]methionine, digestion of proenkephalin-derived peptides with trypsin and carboxy-peptidase B, and quantitation of radioactivity incorporated into Met-enkephalin following reversed-phase HPLC. Nicotine, histamine, and vasoactive intestinal peptide each enhanced the rate of proenkephalin synthesis approximately 10-fold when examined between 16 and 32 h after the drug or hormone addition. Inclusion of nifedipine (1 microM) partially blocked the stimulatory effect of nicotine, but not that of vasoactive intestinal peptide or histamine, or proenkephalin synthesis. Theophylline, tetrabenazine, and angiotensin II also increased the rate of proenkephalin synthesis (three- to eight-fold). These increases in the apparent rate of proenkephalin synthesis were not attributable to altered [35S]methionine specific radioactivity or rates of turnover and did not reflect similar increases in total protein synthesis. The half-life for turnover of Met-enkephalin sequences was 3-4 days in the cultured chromaffin cell. These studies directly show that proenkephalin synthesis is the primary regulatory step in control of chromaffin cell opioid peptide content.

Regulation of both preproenkephalin mRNA and its derived opioids by haloperidol — a method for measurement of peptides and mRNA in the same tissue extract

The goal of this study was to delineate the effects of dopamine antagonists on the regulation of preproenkephalin mRNA and opioid peptides in the rat brain. We have developed a method whereby both mRNA and peptides can be efficiently measured in the same tissue extract, thus reducing the effects of intraspecies variation, differences in dissection and the number of animals required for statistical significance. A sub-chronic dose of haloperidol (3 mg/kg given i.p. in 100 μl DMSO daily for 5 days) produced a 1.8-fold increase ( P < 0.001) in striatal preproenkephalin mRNA levels when compared to animals injected with vehicle dimethyl sulfoxide (DMSO) employing the same schedule. Total opioid peptides as measured by a radioimmunoassay directed to the N-terminus of enkephalins and endorphins were elevated 1.6 fold ( P < 0.001) in the rat striatum. However in other brain regions examined no increases were observed either in preproenkephalin mRNA or the tissue levels of opioid peptides. Analysis of the opioid-like immunoreactive peptides by reverse-phase HPLC analysis showed no dramatic changes in the ratios of the various opioid peptides between haloperidol and vehicle injected animals. Naive animals showed no statistical differences in opioid peptide levels compared to the haloperidol treated animals. There was a statistically significant decrease (30%) in the opioid peptide content of the animals injected with vehicle daily for 5 days when compared with the animals merely sacrificed, or those given acute injections (either with haloperidol or vehicle) the day of sacrifice. We have demonstrated that opioid peptides and mRNA can be measured in the same tissue extract and the data are suggestive that increases in stored opioid peptides may not directly parallel increases in mRNA.

CHANGES IN MET‐ENKEPHALIN AND β‐ENDORPHIN CONTENTS IN THE HYPOTHALAMUS AND THE PITUITARY IN DIABETIC RATS: EFFECTS OF INSULIN THERAPY

1. Immunoreactive (IR)-met-enkephalin and beta-endorphin contents in the hypothalamus and the pituitary were measured in alloxan-diabetic rats with or without insulin treatment. 2. Both IR-met-enkephalin and IR-beta-endorphin in the pituitary were substantially reduced in alloxan-diabetic rats 1 month after treatment. 3. Hypothalamic IR-beta-endorphin content was also significantly lower. 4. Gel-filtration chromatography showed that the peaks co-eluting with met-enkephalin precursor, met-enkephalin and beta-endorphin were lower in the pituitaries from the diabetic rats, whereas the peaks co-eluting with beta-endorphin precursor and beta-lipotropin were not. 5. In another experiment, the IR-beta-endorphin contents of the neuro-intermediate lobe and hypothalamus, but not the anterior lobe were significantly lowered in diabetic rats, whereas IR-met-enkephalin contents were significantly reduced in both the anterior and neuro-intermediate lobe. 6. All these changes were reversed by insulin treatment. 7. As a decrease in general protein synthesis could not explain the recorded changes, these results suggest a possible direct role of insulin in regulating the opioid peptide content of the hypothalamus and pituitary.

Synchronized changes of blood flow in the two common carotid arteries of cats during a systemic pressor response to catecholamines

The effect of long-term (7 weeks) swimming training on the content of beta-endorphin, met- and leu-enkephalins in various brain regions and adrenal glands has been studied in Wistar rats. It has been shown that the adaptation to exercise induced an increase in the content of opioid peptides in most of the brain regions and in adrenal glands. This increase in the level of opioid peptides seems to play an important role in the increase of the resistance to stress.

歯髄におけるｏｐｉｏｉｄ ｐｅｐｔｉｄｅ含量のｂｒａｄｙｋｉｎｉｎによる増大機序

We have previously reported that an increase of the opioid petide content in the rat incisor pulp induced by cavity formation was markedly inhibited following infusion of Des-Arg9- [Leu8] -bradykinin, a potent bradykinin (BK) -antagonist, into the pulp cavity and the inhibitory effect of BK-antagonist was reversed by combination with BK. These findings suggested that BK might be a triggerr in the increase of the pulpal opioid peptide content. In the present study, we examined the BK-effect on the opioid peptide content in in vitro experimental system newly designed by us, using whole incisor pulp of the rat, in order to certify this suggestion. The met-enkephalin (ME) -like peptide content was remarkably increased by BK at a concentration of 1μM, but not in higher concentrations. The effect of BK (1μM) was antagonized with Des-Arg9- [Leu8] -BK (1μM) and was not inhibited by FOY-305 (0.001μM), a trypsin inhibitor. From these results, it was demonstrated that the increase of ME-like peptide content induced by BK was due to activation of an enzyme different from trypsin-like enzyme which was mediated through BK-receptor in the pulp.

Catecholamines and opioid peptides in human phaeochromocytomas.

The tissue contents of catecholamines (CAs) and methionine-enkephalin-like immunoreactivity (Met-enk) were examined in 8 patients with phaeochromocytomas (Phs). In 6, Ph cells were cultured, and the modes of secretion of CAs and Met-enk were examined. Tissue contents of CAs and Met-enk varied from patient to patient, but larger amounts of Met-enk were found in medullary Phs than extramedullary ones, regardless of the secreting CA type. Three patients with extramedullary Phs had clinically showed a sustained hypertension, whereas five with medullary Phs were normotensive or had occasional paroxysmal hypertension. Nicotine (10(-7) M to 10(-4) M) stimulated simultaneous secretion of CAs and Met-enk from the cultured human Ph cells. Met-enk, however, was not secreted in proportion to either epinephrine (E), norepinephrine (NE) or total CAs (E + NE). Met-enk, FK33-824 (FK) (Met-enkephalin analogue), and dynorphin 1-13 (Dyn) significantly suppressed the secretion of CA evoked by 10(-5) M nicotine. The 50% inhibitory concentrations (IC50) of Met-enk, FK, and Dyn were 5 X 10(-6) M, 9.9 X 10(-5) M, and 9.0 X 10(-8) M, respectively, in one patient and 9.0 X 10(-6) M, 1.5 X 10(-7) M, and 1.4 X 10(-7) M in another. In one patient, 10(-5) M naloxone inhibited the CA secretion evoked by 10(-5) M nicotine and did not reverse the 10(-5) M FK-induced suppression of CA secretion in the presence of 10(-5) M nicotine. These results suggest that human Phs may be heterogeneous with regard to storage and secretion of CAs and opioid peptides.(ABSTRACT TRUNCATED AT 250 WORDS)

Altered beta-endorphin, Met- and Leu-enkephalins, and enkephalin-containing peptides in pancreas and pituitary of genetically obese diabetic (db/db) mice during development of diabetic syndrome.

We have recently shown that in addition to beta-endorphin the opioid peptides Met- and Leu-enkephalin and their apparent precursors are localized in islet endocrine cells of the rat pancreas. To begin evaluating a possible role for these pancreatic opiates in the pathophysiology of genetic diabetes in rodents, immunoreactive beta-endorphin and Met- and Leu-enkephalins were measured in acetic acid extracts of pancreas and pituitary of C57BL/KsJ db/db mice and their lean littermates. Groups of animals were studied during three phases of development of the diabetic syndrome in the mutant mice: at 4 (hyperinsulinemic and prediabetic); 6, 9, and 12 (frankly obese and diabetic); and 30 (hypoinsulinemic) wk of age. Elevations or decreases (P less than .05) were found in db/db mice (vs. lean littermates) as follows: pituitary content of Met-enkephalin was twofold higher at all ages studied; pituitary free Leu-enkephalin was lower at 4 wk and reversed to higher at 6-30 wk; pancreatic beta-endorphin was 30% lower at 4 wk and reversed to threefold higher at 6-12 wk; Met- and Leu-enkephalin-containing larger peptides were elevated at one or more points between 6 and 12 wk in both the pancreas and the pituitary. Thus, the onset of overt obesity between 4 and 6 wk of age was accompanied by a marked rise in both pancreatic beta-endorphin and pituitary Leu-enkephalin; similar elevations in these parameters have been reported previously in C57BL/6J ob/ob mice at approximately 12 wk of age.(ABSTRACT TRUNCATED AT 250 WORDS)

Opioid peptides in the cerebrospinal fluid of Alzheimer patients.

Endogenous opioid receptoractive peptides in the cerebrospinal fluid (CSF) of human controls and in those patients diagnosed as having senile dementia of the Alzheimer's type (SDAT) are measured with a radioreceptorassay following HPLC separation. [3H]Etorphine is the ligand used to detect in the HPLC fractions the presence of those endogenous peptides that preferentially interact with several opioid receptors. The RRA uses a receptor-rich P2 fraction extracted from a canine limbic system. The total opioid peptide content found in the HPLC fractions 6-20 (to avoid salts in fractions 1-5) of SDAT CSF (383 +/- 187 pmol ME-equivalents per ml CSF) is significantly higher than the corresponding total from patients with no known neurological disorders (89.1 +/- 46.3 pmol ME-equivalents per ml).

Neuronal cholecystokinin release: morphine and naloxone effects on rat periaqueductal grey

The periaqueductal grey area (PAG) of rat brain is strongly indicated as a major site of opiateand stimulation-induced analgesia. The PAG is thought to integrate perception and response to nociceptive stimuli; afferent projections include major imputs from limbic and sensory areas; efferent projections include those to the spinal cord and nucleus raphe magnus (Beitz, 1982). Apart from its content of opioid peptides, the PAG also contains cholecystokinin octapeptide (CCK), which may be involved in processing of nociceptive stimuli since it reverses morphine-, /I-endorphinand footshock-induced analgesia (Faris et al., 1983). Furthermore, at higher doses CCK is an antinociceptive agent in its own right (Jurna & Zetler, 1981; Sheehan & de Belleroche, 1984). A further indication of a possible interaction between CCK and opiate analgesia systems at the level of the PAG is the finding that the firing of CCK neurons in the EdingerWestphal nucleus of the PAG is reduced by noxious stimuli or intravenous morphine (Innis & Aghajanian, 1985). The following experiments were designed to ascertain whether there is a direct action of opiates on CCKcontaining neurons in the PAG as measured by CCK release. Male CFY rats were killed, their brains removed and the PAG dissected out and chopped (tissue slices 0.3mm thick). The slices were incubated at 37°C in Krebs-bicarbonate medium, pH 7.4, containing 0.5 mMbacitracin and gassed with 95% 0 , / 5 % CO,. After one 10 min preincubation the slices were sequentially transferred to drug-containing medium for a further IOmin, to evaluate basal release and then, for another 5 min, to a third chamber containing the drug plus high K + ion concentration (34 mM) to evoke neurotransmitter release. After incubation, tissue slices were placed in 90% CH30H/IO% H,O, O'C, and sonicated to extract low molecular weight forms of CCK. The methanolic extracts were dried under nitrogen and rehydrated before assay. The supernatants from the incubation vials were frozen until used for assay. Tissue and released levels of CCK were measured by radioimmunoassay with antisera Ab2717 (a generous gift from Professor J. Rehfeld) against monoiodinated human gastrin (2-17) as a tracer. Tissue slices were exposed to morphine hydrochloride ( 10-'0-10-' M) or naloxone hydrochloride ( l o ' 1 0 6 ~ ) . Two Caz+ ion concentrations were used for the experiments with morphine, 0.6 mM or 2.5 mM, to evaluate whether any morphine action was Ca2+ dependent.

Opioid peptides in human adrenal: partial characterization and presence of adrenal peptide E.

Evaluation of hypotheses concerning the role of opioid peptides in the human adrenal is handicapped by the lack of information concerning the nature of these peptides. We studied the content of opioid peptides in whole adrenal tissue using several RIAs, including one which cross-reacts with all opioid peptides tested. Opioid peptides were localized to granules which behaved like chromaffin granules on crude sucrose density separation. beta-Endorphin immunoreactivity was a minor component, which was found principally in the form of beta-endorphin-(1-31). The majority of the remaining peptides probably were products of proenkephalin. The human postmortem tissue differed from bovine tissue in that the major accumulating products of this precursor were the size of the enkephalins and their small congeners, and not the intermediate-sized (mol wt, approximately 1500-4000) peptides that predominated in bovine tissue. We also found evidence of the presence of the 25-amino acid complex opioid, peptide E, in human tissue.