Acetylated and nonacetylated forms of beta-endorphin in rat brain and pituitary

Characterization of pro-opiomelanocortin processing in heterologous neuronal cells that express PC2 mRNA

We have investigated processing of monkey pro-opiomelanocortin (POMC) following transfection into heterologous neuronal Neuro 2A (N2A) cells. In several separately transfected stable cell lines (termed N2A/POMC2-like; n = 4), POMC was processed to beta E only, by direct cleavage from the precursor. Thus, these cell lines did not produce beta E in the orderly manner observed in the pituitary, that is, via the intermediate peptide beta LPH. Analysis of one representative N2A/POMC2 cell line revealed that the extent of processing to beta E appeared to be negatively correlated with precursor expression level, suggesting that the processing enzyme(s) in these cells was present in limiting amounts. Northern analysis of PC1 and PC2, two recently cloned processing enzymes, showed that N2A/POMC2 cells expressed low levels of PC2 mRNA, but no detectable PC1 mRNA. These data suggest that (1) the order of processing observed in the pituitary is not exclusively determined by tertiary folding of the precursor, but rather by the complement of processing enzymes in a particular cell, and (2) if PC2 is responsible for POMC processing in N2A/POMC2 cells, this enzyme, expressed in limiting amounts, appeared to show selectivity for the beta E amino terminal processing site.

Effects of morphine treatment on pro-opiomelanocortin systems in rat brain

In previous studies to determine whether chronic opiate administration might negatively feedback upon endogenous opioid systems in the CNS, investigators found no changes in steady-state concentrations of opioid peptides following morphine pelleting. However, since only steady-state levels were measured, it was still not clear whether morphine treatment altered the release and/or biosynthesis of opioid-containing neurons. The goal of the present study was to assess the effects of chronic morphine pelleting on the dynamics of beta-endorphin (beta E) biosynthesis in rats. Hence, at several times during a 7-day morphine treatment, concentrations of total beta E-immunoreactivity (-ir), as well as chromatographically sieved forms of beta E, were determined by RIA, and mRNA levels of pro-opiomelanocortin (POMC) were measured by a solution phase protection assay using a mouse or rat POMC 32P-labelled riboprobe. Concentrations of total beta E-ir or different forms of beta E-ir peptides (i.e. beta-lipotropin, beta E1-31, or beta E1-27/beta E1-26) in the hypothalamus or midbrain following either 1 or 7 days of treatment were similar in morphine- and placebo-pelleted animals. However, a significant increase in total hypothalamic beta E-ir was observed following 3 days of morphine pelleting; chromatographic analyses indicated that this was primarily due to a selective increase in the opiate inactive forms of beta E, i.e. beta E1-27/beta E1-26. After 7 days of pelleting, morphine-treated animals tended to have lower POMC mRNA levels than those of placebo controls (20 to 50% decrease in different studies). The accumulation of hypothalamic beta E-ir at 3 days, and the apparent decline in POMC mRNA levels at 7 days, lend support to the hypothesis that morphine negatively feeds back upon POMC neurons in the brain by inhibiting beta E release and biosynthesis.

In vitro release of hypothalamic beta-endorphin (beta E) by arginine vasopressin, corticotropin-releasing hormone and 5-hydroxytryptamine: evidence for release of opioid active and inactive beta E forms

The aims of the present experiments were: 1) to test whether substances which modulate beta-endorphin-immunoreactive (beta E-ir) release from the pituitary gland might act similarly in hypothalamic tissue; and 2) to further characterize the beta E-ir forms which are released from hypothalamus. To address these questions, hypothalamic tissue was incubated in vitro for 10 min periods in either normal media (basal conditions) or in media containing 55 mM KCl or one of several other test substances (stimulation conditions) and release was estimated by measuring the beta E-ir concentrations in the media. Depolarizing concentrations of K+ increased beta E-ir release 2-3 fold over basal levels and this effect appeared to be Ca2(+)-dependent. Dose-dependent increases in beta E-ir release were elicited by nanonolar to micromolar concentrations of either corticotropin-releasing hormone (CRH), arginine vasopressin (AVP), or 5-hydroxytryptamine (5-HT). Conversely, dopamine (1 microM) inhibited both the basal and K(+)-stimulated release of beta E-ir from hypothalamus. Gel filtration chromatography revealed that beta E1-31 and beta E1-27/beta E1-26 were the primary beta E-ir peptides released under either basal or CRH-stimulated conditions; the relative amounts of the beta E-ir peptides found in the media were nearly identical to those found in the hypothalamus itself. This result indicates that the release of different beta E-ir peptides into the media appears to be proportional to the relative amounts stored in tissue.(ABSTRACT TRUNCATED AT 250 WORDS)

Beta-endorphin in the brainstem and the cerebellum of the human infant: regional levels' profile assessed with immunoaffinity chromatography and solid phase radioimmunoassay

The regional levels' profile of human beta-endorphin (beta h-EP) was studied in the brainstem and the cerebellum of 16 infant victims of "Sudden Infant Death Syndrome" and other death causes. An immunoaffinity chromatography procedure based on a monoclonal antibody directed specifically against the N-terminus of beta-EP was used to extract this peptide from the tissue samples. Beta-EP was then assessed quantitatively by means of a very sensitive solid phase radioimmunoassay (using a polyclonal antibody specific for the C-terminus of beta-EP) developed especially for the study presented here.

Forms of immunoreactive beta-endorphin in the intermediate pituitary of the holostean fish, Amia calva

Acid extracts of the intermediate pituitary of the holostean fish, Amia calva, were fractionated by gel filtration chromatography and analyzed with radioimmunoassays specific for N-acetylated beta-endorphin and C-terminally amidated alpha-MSH. In these extracts beta-endorphin-related immunoreactive material and alpha-MSH-related immunoreactive material were present in roughly equimolar amounts. The immunoreactive beta-endorphin-sized material was tested for opiate receptor binding activity using a beta-endorphin radioreceptor assay. The results of these studies were negative. The immunoreactive beta-endorphin-sized material was further analyzed by cation exchange chromatography at pH 2.5. Two major and three minor peaks of immunoreactive material were isolated. Peak 5 exhibited a net charge of +7 at pH 2.5 and represented 53% of the total immunoreactivity recovered. Peak 2 with a net charge of +3 at this pH represented 38% of the total immunoreactivity recovered. The minor forms, Peaks 1, 3 and 4, exhibited net charges of +2, +4 and +6, respectively. The apparent molecular weights of Peaks 2 and 5 were determined on a Sephadex G-50 column. Peak 2 had an apparent molecular weight of 2.7 Kd and Peak 5 had an apparent molecular weight of 3.5 Kd. Reverse phase HPLC analysis of Peak 5 indicates that this form of Amia beta-endorphin had chromatographic properties similar to salmon beta-endorphin II. These results would suggest that N-terminal acetylation and C-terminal proteolytic cleavage are important post-translational modifications of the forms of Amia beta-endorphin.

Isolation of immunoreactive beta-endorphin-related and Met-enkephalin-related peptides from the posterior pituitary of the amphibian, Xenopus laevis

Acid extracts of the posterior pituitary of the amphibian, Xenopus laevis, were analyzed with two heterologous region specific beta-endorphin RIAs. Following gel filtration chromatography and cation exchange chromatography four peaks of immunoreactivity were detected. All four peaks were detected with a N-acetyl specific beta-endorphin RIA. Peak I represented 92% of the total immunoreactivity isolated following cation exchange chromatography. This peak had a net positive charge at pH 2.5 of +1 and an apparent molecular weight of 1.4 Kd. Following reverse phase HPLC, Peak I fractionated into two peaks: Peak Ia and Peak Ib. Both peaks were detected with the N-acetyl specific beta-endorphin RIA and a Met-enkephalin RIA, however, neither peak co-migrated with either Met-enkephalin or N-acetyl-beta-endorphin(1-16). At present it is not clear whether Peak I is derived from pro-opiomelanocortin or one of the other opioid polyproteins. Peaks II, III, and IV represented 8% of the total immunoreactivity recovered following cation exchange chromatography. These peaks had net positive charges of +3, +4, and +5, respectively, and apparent molecular weights of 2.8, 3.2, and 3.5 Kd, respectively. These apparently N-acetylated beta-endorphin-sized forms are minor end products of the pro-opiomelanocortin biosynthetic pathway.

Isolation of enzyme cDNA clones by enzyme immunodetection assay: isolation of a peptide acetyltransferase

The biological activity of many proteins and peptides can be profoundly affected by enzyme-catalyzed covalent modifications such as acetylation, sulfation, glycosylation, or amidation. This article describes the cloning of such an enzyme, a peptide acetyltransferase from rat brain that catalyzes the amino-terminal acetylation of endorphins and perhaps other substrates in vivo. Blot-hybridization analysis suggests that the mRNA encoding the acetyltransferase is approximately 2.0 kilobases, is present in whole rat brain and rat hypothalamus, and is slightly larger in mouse AtT20 tumor cells. The acetyltransferase was cloned by using a strategy whereby a cDNA expression library was screened with a solid-phase enzyme-activity assay; this technique combines the use of the substrate coupled to a solid support and subsequent recognition of the product by using a specific antiserum. We have called this method the enzyme immunodetection assay (EIDA). The EIDA should prove useful in the isolation of other clones for proteins that possess enzymatic activity upon expression in bacterial hosts.

Characterization of the forms of beta-endorphin and alpha-MSH in the caudal medulla of the rat and guinea pig

The post-translational processing of pro-opiomelanocortin (POMC) in brain remains controversial. Classically, there was thought to be a single cell group in the arcuate nucleus with long projections through limbic structures. More recently, a second cell group was discovered in the caudal medulla. This study addresses the question of POMC processing in this region. Steady-state analysis of acid extracts of dorsal caudal medulla from rat and guinea pig CNS by gel filtration chromatography and radioimmunoassay indicated that in both species the major POMC-related end products are alpha-MSH-sized material and beta-endorphin-sized. In this tissue beta-LPH and ACTH represent minor end products. Analysis of the alpha-MSH-sized material from both species by reverse-phase HPLC indicated that in the rat caudal medulla approximately 79% of the alpha-MSH-related material is acetylated, and in the guinea pig caudal medulla approximately 85% of the alpha-MSH-related material is acetylated. Analysis of the forms of beta-endorphin isolated from the rat caudal medulla by cation exchange chromatography revealed that acetylated and non-acetylated forms of beta-endorphin are present in this region of the rat CNS. Approximately 65% of the beta-endorphin in the rat caudal medulla is N-acetylated. Analysis of the forms of beta-endorphin isolated from the guinea pig caudal medulla indicated that approximately 63% of the beta-endorphin is N-acetylated in this region of the guinea pig CNS. These data indicate that the post-translational processing of POMC in the dorsal caudal medulla, the site of the nucleus tractus solitarius POMC cell group, is distinct from the processing patterns that have been reported for POMC systems in the mammalian anterior pituitary, intermediate pituitary and arcuate nucleus.

Characterization of endorphins from the pituitary of the spiny dogfish Squalus acanthias

Opioid-like immunoreactive material was extracted from the pituitary and brain of the Spiny Dogfish Shark Squalus acanthias. The immunoreactive material in the pituitary extracts was purified to apparent homogeneity by reverse phase high performance liquid chromatography and subsequently characterized by amino acid analysis, Edman degradation and fast atom bombardment mass spectrometry. The largest opioid-like peptide isolated contained 30 amino acids and showed 80 percent homology with salmon endorphin-II but less than 50 percent homology with human beta-endorphin. Three structural variants of this molecule were also characterized. These variants were shown to be shorter N-terminal fragments, two of which corresponded to cleavage products at the single basic residues arginine and lysine. Cleavage at a single lysine residue has not been reported for posttranslational processing of beta-endorphin in mammals and could represent a modification seen only in lower vertebrates. The remaining fragment corresponded to a loss of 3 residues from the C-terminus of the parent molecule. No alpha-N-acetylated peptides were detected. These results provide the first unequivocal confirmation of beta-endorphin in an elasmobranch and provide evidence of novel N-terminal variants of beta-endorphin.

Changes in the processing of beta-endorphin in the hypothalamus and pituitary gland of female rats during sexual maturation

Puberty in the female rat is accompanied by a marked attenuation of the opioid inhibition of luteinizing hormone secretion. One factor which may contribute to this altered role is a change in the metabolism of opioid peptides during sexual maturation. beta-Endorphin undergoes a considerable degree of metabolism through both C-terminal proteolysis and N-acetylation, and these metabolites do not possess opioid activity. The processing of beta-endorphin in the hypothalamus and in the anterior and neurointermediate lobes of the pituitary gland in prepubertal and adult female rats was studied using gel filtration and high performance liquid chromatography coupled with radioimmunoassay. In the anterior lobe, high molecular weight precursors of beta-endorphin (pro-opiomelanocortin and beta-lipotropin) were present in prepubertal (28 days old) rats, but little authentic beta-endorphin was detected. In contrast, only beta-lipotropin and beta-endorphin were present in mature (70 days old) animals. Only beta-endorphin-sized peptides were present in the neurointermediate lobes of both prepubertal and adult rats. However, the proportion of N-acetylated metabolites was higher in sexually mature animals. In the hypothalamus, only beta-endorphin-sized peptides were present in both juvenile and adult animals. However, C-terminal proteolysis increased with age (no acetylated metabolites were detectable in this tissue). The proportion of the total beta-endorphin-like immunoreactivity attributable to beta-endorphin was lower in young adult (first dioestrus after vaginal opening) (55%) and mature (dioestrus, 61-64 days old) rats (56%) compared to prepubertal (30 days old) animals (75%) and the proportions of non-acetylated metabolites [beta-endorphin-(1-27) in young adults and beta-endorphin-(1-26) in adults] were increased concomitantly. These changes were correlated with a reduced luteinizing hormone response to the opiate antagonist naloxone in adult compared to prepubertal rats. beta-Endorphin is processed differently in the two lobes of the pituitary gland and in the hypothalamus and the degree of metabolism increases as the rat reaches sexual maturity. The increased metabolism of beta-endorphin in the hypothalamus, the site most likely to be involved in the control of luteinizing hormone secretion, results in a reduction in the relative proportion of the opioid active parent peptide. Thus, increased inactivation of beta-endorphin may contribute to the attenuation of the opioid inhibition of luteinizing hormone secretion observed during puberty.

N alpha-Acetyl-gamma-endorphin is an endogenous non-opioid neuropeptide with biological activity

N alpha-acetyl-gamma-endorphin (Ac gamma E) was identified in the rat neurointermediate pituitary, based on its immunological properties, comigration with synthetic Ac gamma E on HPLC and resistance to aminopeptidase-M degradation. The peptide appeared to be the main form of gamma-endorphin (gamma E) in this tissue and in brain areas remote from the hypothalamus (hippocampus, septum, amygdala). The anterior pituitary, the hypothalamus and the thalamus contained almost exclusively the non-acetylated form of gamma E. In contrast to gamma E, Ac gamma E was completely devoid of specific affinity for brain opiate binding sites. Yet, the peptide mimicked gamma E in that it potently attenuated passive avoidance behaviour in rats, when injected topically into the nucleus accumbens. It is concluded that Ac gamma E is an endogenous neuropeptide with non-opioid biological activity. N alpha-acetylation may not merely represent a mechanism for the inactivation of opioid activities of endorphins, but rather allow the organism to select specific sets of biological activities that reside in the endorphin structure.

Ultrastructural evidence for beta-endorphin-like immunoreactivity in the nervous system of the rat duodenum

Using a modified immunoelectron microscopic staining technique the opioid peptide beta-endorphin could be demonstrated within large dense-core vesicles (LDVs) which are localized in presumptive axons and dendrites of the duodenal myenteric plexus of the rat duodenum. Pre-absorption tests with synthetic beta-endorphin (10(-6)M, final concentration) abolished the beta-endorphin immunoreactivity, resulting in only beta-endorphin unstained vesicles. To demonstrate more clearly electron-dense beta-endorphin material within vesicles the ultrathin sections were not counterstained with heavy metal salts. These sections revealed that the beta-endorphin material is localized as 'cores' with a mean diameter of 35-50 nm within LDVs corresponding to cores of LDVs, which are 70-90 nm in mean diameter.

Corticotropin-releasing factor: immunohistochemical colocalization with adrenocorticotropin and beta-endorphin, but not with Met-enkephalin, in subpopulations of duodenal perikarya of rat

By the use of two different double-staining techniques (simultaneous staining of adjacent serial sections and the double-staining elution method) it was possible to demonstrate that a corticotropin-releasing factor (CRF) immunofluorescence co-existed with an adrenocorticotropin (ACTH) and beta-endorphin (beta-END) immunoreactivity, but not with a Met-enkephalin (Met-ENK) immunostaining, within perikarya subpopulations of both the myenteric and submucousal plexus of the rat duodenum. Not a single Met-ENK-positive neuronal cell body was stained also for CRF, ACTH or beta-END. Even nerve fibres, localized in both the myenteric plexus and closely to submucousal blood vessels (probably arterioles), revealed a CRF immunofluorescence, which is also colocalized with an beta-END staining. These results are quite different to the recent observations in the mammalian hypothalamus, suggesting that some myenteric and submucousal plexus neurons may synthesize CRF as well as beta-END and ACTH, but not Met-ENK. The colocalized peptides might be concomitantly released into the synaptic cleft after terminal stimulation.

N-acetyl endorphin in rat spermatogonia and primary spermatocytes

In previous reports modest levels of beta-endorphin have been found by radioimmunoassay in rat testis, and localized by immunofluorescence to the interstitial cells. We have confirmed these previous reports and extended them by showing that the majority of testicular endorphins are acetylated forms, N-acetyl gamma-endorphin, N-acetyl alpha-endorphin, and N-acetyl beta-endorphin1-27. In addition, N-acetylated endorphins are not found in interstitial cells, but are confined to spermatogonia and primary spermatocytes.

Identification and possible function of pro-opiomelanocortin-derived peptides in the testis

Using antibodies against peptides derived from different portions of the POMC molecule, immunocytochemical evidence suggests that this precursor and/or the peptides present within it are localized in testicular Leydig cells of at least five species. There is no evidence for the localization of these peptides or their precursor in any other cell type in this organ. Examination of testicular extracts by gel filtration, SDS-PAGE, and RP-HPLC indicate that the testis contains low concentrations of POMC-derived peptides relative to brain. Further analysis indicates that POMC is processed to alpha-MSH and beta-endorphin similar to its processing in intermediate pituitary lobe and brain. The relative mobilities of immunoreactive alpha-MSH and beta-endorphin on RP-HPLC columns indicate that they are in the unacetylated state as in brain and in contrast to the acetylated forms in the intermediate pituitary lobe. The potential for Leydig cells to synthesize POMC and its peptides was suggested by the demonstration of POMC-like mRNA in total testis and Leydig cell cultures. The size of the POMC-like mRNA is approximately 150 base pairs shorter than anterior or intermediate pituitary POMC mRNA. POMC-like mRNA activity has also been localized to Leydig cells in sections of testes using in situ hybridization. Immunostainable beta-endorphin and other POMC-derived peptides are present in testicular Leydig cells during fetal life and following puberty at times when testosterone secretion is maximal. The accumulation of immunostainable POMC-derived peptides in Leydig cells is dramatically increased by LH and hCG. A variety of observations suggests that testicular cells can respond to POMC-derived peptides. ACTH and the MSHs stimulate growth and cAMP accumulation in Sertoli cells. By contrast, studies using antagonists suggested that beta-endorphin and/or another testicular opioid inhibit Sertoli cell proliferation and ABP secretion. These observations are consistent with the postulate that different portions of the POMC molecule may have opposite effects on Sertoli cell function and suggest a mechanism by which Leydig cells could modulate Sertoli cell activity. Intratesticular administration of opiate antagonists inhibits testosterone secretion both in vivo and in vitro. These observations suggest that Leydig cell-derived beta-endorphin may facilitate testosterone secretion either directly or indirectly. The finding of POMC and its derivative peptides in testis, ovary, adrenal, and placenta suggests that all steroid hormone-secreting organs in mammals may utilize this peptidergic system.

Characterization and localization of proopiomelanocortin messenger RNA in the adult rat testis

Northern blot analysis of total RNA and polyadenylated RNA isolated from adult rat testes showed that a proopiomelanocortin (POMC)-like messenger RNA molecule is present in these extracts. The testicular POMC messenger RNA is comparable in length to amygdala and midbrain POMC messenger RNA and appears to be at least 200 nucleotides shorter than POMC messenger RNA found in the hypothalamus and anterior and intermediate lobes of the pituitary gland. Hybridization in situ showed that POMC messenger RNA is located in Leydig cells, which are the only testicular cells that contain immunostainable POMC-derived peptides. These results suggest that local synthesis of POMC occurs in the testis.

Corticotropin-releasing factor is contained within perikarya and nerve fibres of rat duodenum

Immunofluorescence microscopic studies revealed a corticotropin-releasing factor (CRF) staining within both myenteric plexus perikarya and nerve fibres of the rat duodenum. A CRF-immunofluorescence could be visualized also within nerve fibres close associated with myenteric and submucous blood vessels. Even the lamina propria contained CRF-immunoreactive nerve fibres, which were obviously often localized near the basal lamina.

alpha-melanotropin and beta-endorphin-like immunoreactivities are contained within neurons and nerve fibers of the rat duodenum

Both alpha-melanotropin and beta-endorphin were revealed by immunofluorescence microscopy studies within neurons and nerve fibers of the rat duodenum. An immunohistochemical staining for alpha-melanotropin was seen within neuronal cell bodies and nerve fibers bundles of the myenteric and submucous plexus. A beta-endorphin immunofluorescence was visualized within perikarya and nerve fibers of both the myenteric and submucous plexus. alpha-Melanotropin as well as beta-endorphin immunoreactivities were strictly localized to structures of the enteric nervous system. In crypts and epithelial cells only a non-specific staining was observed.

Chemical and immunological characterization of salmon endorphins

Five new peptides related to salmon N-acetyl endorphin II (N-Ac-EP II) were isolated from an acid acetone extract of the pituitary. They were identified as EP II and four N-terminal fragments of N-Ac-EP II, namely N-Ac-EP II (1-18), (1-19), (1-20), and (1-29). The sequence comparison with mammalian EPs revealed that N-Ac-EP II (1-18) and (1-19) corresponded to mammalian alpha- and gamma-EP, respectively. The occurrence of peptides similar to mammalian alpha-, beta-, and gamma-EP indicates that further processing of EP takes place in both the teleost and mammalian pituitaries by similar pathways. A radioimmunoassay for salmon EPs has been developed with rabbit antiserum raised against salmon N-Ac-EP II. It was demonstrated that the antiserum showed full cross-reactivity with salmon N-Ac-EP I, N-Ac-EP II (1-20), and N-Ac-EP II (1-18), but none with Met-enkephalin, human beta-EP, and human beta-LPH. Similarly, the salmon EPs did not cross-react with human beta-EP antiserum in the radioimmunoassay.

Adrenocorticotropin and beta-endorphin are colocalized in the nervous system of rat duodenum

Adrenocorticotropin and beta-endorphin-like immunoreactivities were visualized by an immunohistochemical method on adjacent serial sections of the nervous system of the rat duodenum. Perikarya lying in the myenteric plexus and stained alternately for ACTH or beta-endorphin, showed on two adjacent serial sections a co-existence of these two peptides within one and the same perikarya. A co-localization of beta-endorphin and ACTH is not demonstrated with certainty in the submucous plexus. These results may be evidence for a common occurrence of the two peptides within perikarya of the rat duodenum.

Brain peptides: what, where, and why?

Within the past decade, a large number of peptides have been described within the vertebrate central nervous system. Some of these peptides were previously known to be present in nonneural vertebrate tissues, as well as in lower species, in which they may serve as primitive elements of intercellular communication prior to the development of neuronal or endocrine systems. In vertebrates, these peptides are thought to have neurotransmitter or neuromodulatory roles and appear to be involved in the regulation of a number of homeostatic systems, although the mechanisms of their actions are still unclear.

Biosynthesis of multiple forms of beta-endorphin in the reptile intermediate pituitary

Fractionation of the beta-endorphin-sized material from freshly dissected reptile intermediate pituitaries by ion exchange chromatography on sulfopropyl Sephadex (SP) revealed at least three distinct forms of immunoreactive beta-endorphin. These forms eluted at 0.25 M NaCl, 0.28 M NaCl, and 0.32 M NaCl and represent respectively, 6%, 65% and 29% of the total immunoreactivity. Only the 0.28 M NaCl peak and the 0.32 M NaCl peak exhibited naloxone reversible opiate bioactivity when tested in the isolated guinea pig ileum bioassay system; taking into account the molar amount of immunoreactive peptides the 0.32 M NaCl peak was 6 fold more potent than the 0.28 M NaCl peak. Intermediate pituitaries in culture were incubated with either [3H]tyrosine, [3H]arginine, or [35S]methionine for periods up to 24 hours and beta-endorphin-sized peptides were prepared by immunoprecipitation and gel filtration. Fractionation of the labeled beta-endorphin-sized peptides by ion exchange chromatography yielded profiles nearly identical to the immunoassay analyses of freshly dissected tissue. Further analysis of the major labeled forms of reptile beta-endorphin by chromatography on Sephadex G-50 equilibrated in 6 M guanidine HCl indicated that the 0.32 M NaCl peak had an apparent molecular weight of 3500 +/- 100 and the 0.28 M NaCl peak had an apparent molecular weight of 3200 +/- 100. Furthermore, pulse/chase experiments showed that the 0.32 M NaCl peak was the precursor for the 0.28 M NaCl peak. These results coupled with the relative opiate bioactivities of the major argue that the principal post-translational modification of reptile beta-endorphin is COOH-terminal proteolytic cleavage.

Identification of pro-opiomelanocortin-derived peptides in the human adrenal medulla

Extracts from adult human adrenals contained high concentrations of immunoreactive beta-endorphin and alpha-melanotropin. Lower quantities of immunoreactive adrenocorticotropic hormone could also be detected. Distribution studies showed the presence of pro-opiomelanocortin fragments in the adrenal medulla. No alpha-melanotropin, beta-endorphin, or adrenocorticotropic hormone could be found in adrenal extracts from several other mammalian species. Analysis of the beta-endorphin-like immunoreactivity using region specific radioimmunoassays interfacing with gel filtration and reverse-phase high-performance liquid chromatography showed the majority of the beta-endorphin-like material to exist as nonacetylated beta-endorphin-(1-31) with a small percentage of lipotropin-sized molecules. The alpha-melanotropin-like immunoreactivity cochromatographed on gel filtration and reverse-phase high-performance liquid chromatography with desacetyl alpha-melanotropin. The data suggest that pro-opiomelanocortin is expressed in the adrenal medulla of humans but is not detectable in the adrenal glands of many other mammalian species.

Characterization of beta-endorphin immunoreactive peptides in rat pituitary and brain by coupled gel and reversed-phase high-performance liquid chromatography

A procedure which combines gel high-performance liquid chromatography (HPLC) and reversed-phase HPLC in two systems with radioimmunoassay was developed for the analysis of beta-endorphin (beta END)-related peptides in rat pituitary and brain. The gel HPLC system allows rapid screening for relative amounts of precursors and products involved in beta END biosynthesis. Reversed-phase HPLC reveals minor post-translational modifications, such as acetylation, which greatly alter the biological activity of beta END. The application of this coupled procedure clearly demonstrates tissue-specific differences in the processing of beta END in pituitary and brain regions and indicates that the system may be generally applicable to the analysis of neuropeptide heterogeneity.

Measurement of total opioid peptides in rat brain and pituitary by radioimmunoassay directed at the alpha-N-acetyl derivative

A sensitive assay, which cross-reacts with and is specific for diverse opioid peptides, is described. This is based on the prior acetylation of samples and subsequent radioimmunoassay with an antiserum highly specific for the acetylated NH2 terminus of opioid peptides. The result is a procedure that can be used to investigate multiple forms of opioid peptides in extracts of biological material. The sensitivity of the assay is approximately 15 fmol of beta-endorphin per incubation tube, i.e., approximately 100-fold greater sensitivity than the radioreceptor assay used in our laboratory. The peptide concentration required for 50% displacement of trace ranged from 0.65 nM (beta-endorphin) to 1.6 nM (Met-enkephalin). The assay apparently shows an absolute requirement for a free (or acetylated) NH2 terminus corresponding to either a Leu- or Met-enkephalin sequence. Use of the assay with and without prior acetylation of sample provides a method for estimation of the ratio of acetylated:nonacetylated opioid peptides in crude or fractionated extracts. The procedure is used to investigate the forms of opioid peptide found in rat brain and pituitary.

Regional heterogeneity in the processing of pro-opiomelanocortin in rat brain

The occurrence of alpha-N-acetylated forms of beta-endorphin (beta END) and alpha-melanotropin (alpha MSH) in rat pituitary and brain regions was investigated using high-performance liquid chromatography and radioimmunoassay. Acetylated derivatives of both peptides predominated in neurointermediate pituitary but represented minor components in anterior pituitary, in agreement with previous reports. Regional differences in the degree of acetylation were also observed in brain. Arcuate nucleus, the major source of beta END and alpha MSH in brain, contained small amounts of acetylated forms but most of the immunoreactivity chromatographed with the unmodified beta END 1-31 and des-acetyl-alpha MSH. Amygdala and periaquaductal grey contained the non-acetylated forms only, whereas in nucleus accumbens the major immunoreactive species were the acetylated derivatives of beta END 1-31 and beta END 1-27 along with the mono- and di-acetyl forms of alpha MSH. The selective distribution of acetylated beta END and alpha MSH suggests heterogeneity in the processing of POMC in brain and may indicate a role for alpha-N-acetylation in regulating the biological activities of these peptides in specific brain regions.

Pro-opiocortin processing in the pituitary: a model for neuropeptide biosynthesis

The biosynthesis of alpha-MSH, beta-endorphin and ACTH in the pituitary is reviewed. These neuropeptides are synthesized from a common pro-protein, pro-opiomelanocortin. The pro-protein is cleaved intragranularly, at pairs of basic residues in the molecule to yield the respective peptide products. An unique, thiol protease (pro-opiocortin converting enzyme) and a carboxypeptidase B-like enzyme, both localized within pituitary secretory granules and having a pH optimum of 5-6, appear to be involved in the proteolytic processing of pro-opiomelanocortin.

Immunohistochemical distribution of alpha-neo-endorphin/dynorphin neuronal systems in rat brain: evidence for colocalization

alpha-Neo-endorphin and dynorphin immunoreactivities in rat brain were visualized by double antibody immunofluorescence of frozen sections. Antibodies were used that were specific for their respective antigens. The pattern of neuronal immunostaining produced by alpha-neo-endorphin and dynorphin antisera in adjacent serial sections was completely superimposible. No areas were found in which alpha-neo-endorphin or dynorphin immunoreactivities existed alone. The following brain regions contained alpha-neo-endorphin/dynorphin-immunoreactive fibers and terminals: the median forebrain bundle, the internal capsule, the substantia nigra, the hypothalamus, the nucleus accumbens, the hippocampus, and the medulla oblongata. A few fibers were seen in the cerebral cortex and in the corpus striatum. In many regions, this neuronal fiber system seems to overlap the neuronal system previously described to contain [Met]-/[Leu]enkephalin-immunoreactive material. In brains from colchicine-treated animals, numerous alpha-neo-endorphin/dynorphin-immunoreactive neuronal cell bodies were seen in the supraoptic, retrochiasmatic supraoptic, paraventricular, and magnocellular accessory nuclei of the hypothalamus. It is concluded that alpha-neo-endorphin-like and dynorphin-like immunoreactivities are part of the same neuronal system.