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Carp beta-endorphin is posttranslationally modified by N-terminal acetylation and C-terminal cleavage. These processes determine the biological activity of the beta-endorphins. Forms of beta-endorphin were identified in the pars intermedia and the pars distalis of the pituitary gland of the common carp (Cyprinus carpio), as well as the forms released in vitro and into the blood. After separation and quantitation by high performance liquid chromatography (HPLC) coupled with radioimmunoassay, the beta-endorphin immunoreactive products were identified by electrospray ionisation mass spectrometry and peptide sequencing. The release of beta-endorphins by the pituitary gland was studied after stimulation with corticotrophin-releasing factor (CRF) in vitro. In the pars intermedia, eight N-acetylated truncated forms were identified. Full length N-acetyl beta-endorphin(1-33) coeluted with N-acetyl beta-endorphin(1-29) and these forms together amounted to over 50% of total immunoreactivity. These products were partially processed to N-acetyl betaendorphin(1-15) (30.8% of total immunoreactivity) and N-acetyl beta-endorphin(1-10) (3.1%) via two different cleavage pathways. The acetylated carp homologues of mammalian alpha- and gamma-endorphin were also found. N-acetyl beta-endorphin(1-15) and (1-29) and/or (1-33) were the major products to be released in vitro, and were the only acetylated beta-endorphins found in blood plasma, although never together. CRF stimulated the release of opioid beta-endorphin from the pars distalis. This non-acetylated beta-endorphin represents the full length peptide and is the most abundant form in plasma.

We have previously reported that hypophysial neurointermediate lobe peptides, di-acetylated alpha-melanocyte-stimulating hormone (di-ac-alpha-MSH) and N-acetylated beta-endorphin (N-ac-beta-END), can acutely increase the relative number of prolactin-secreting cells in anterior pituitary cell cultures from ovariectomized rats. Inasmuch as the des-acetylated forms of these peptides (des-ac-alpha-MSH and beta-END) were not effective in this regard, we concluded that acetylation was an absolute requirement for manifestation of the recruitment response. The aim of the present study was to determine whether these des-acetylated variants could antagonize the mammotrope-recruiting activity of their acetylated congeners. Treatment of anterior pituitary cell cultures with di-ac-alpha-MSH and N-ac-beta-END increased the relative amount of prolactin secretors above control values. Interestingly, des-acetylated variants of alpha-MSH and beta-END blocked the mammotrope-recruitment activity of their respective acetylated forms. In addition, beta-END antagonized the mammotrope-recruitment activity of di-ac-alpha-MSH while des-ac-alpha-MSH did not attenuate the stimulatory effect of N-ac-beta-END. Given that mammotropes maintained in vivo are exposed to all these peptides, it is possible that these acetylated and non-acetylated congeners may act in an opposing manner to regulate dynamic prolactin release.

beta-Endorphin- and alpha-melanotrophin (alpha-MSH)-related peptides were extracted from the pars intermedia of Xenopus laevis maintained for 2, 4 or 6 weeks on a white background and for the same periods on a black background. The peptides were resolved under dissociating conditions by gel exclusion chromatography on Sephadex G-50 and they were detected by radioimmunoassay with antibodies to beta-endorphin, alpha,N-acetyl beta-endorphin and alpha-MSH. The beta-endorphin-related peptides separated into two fractions of different molecular size. Further purification of the peptides in each fraction was by ion exchange chromatography on SP-Sephadex C-25 and by high-pressure liquid chromatography. The alpha-MSH-related peptides were resolved by gel exclusion and ion exchange chromatography. The purified beta-endorphin- and alpha-MSH-immunoreactive peptides were identified by comparison of their chromatographic properties with the corresponding peptides from porcine pituitary or by comparison with synthetic peptides. The major form of beta-endorphin in the pars intermedia of the frog adapted to a white background was identified as alpha,N-acetyl beta-endorphin (1-8); it was accompanied by a small quantity of acetylated peptides with molecular size similar to beta-endorphin. In contrast, the pars intermedia of the frogs adapted to a black background contained approximately equal amounts of alpha,N-acetyl beta-endorphin (1-8) and the larger forms of beta-endorphin. The higher molecular weight forms were identified as the alpha,N-acetyl derivatives of beta-endorphin (1-26), (1-27) and (1-31); however after 6 weeks of white adaptation the sole remaining peptide in this group was the 26-residue peptide. An additional beta-endorphin immunoreactive peptide, provisionally identified as beta-endorphin (10-26), was present in both black- and white-adapted animals; the amounts of this peptide increased during white adaptation. Major differences in the processing of alpha-MSH were also observed. In the frogs adapted to a black background des-acetyl alpha-MSH greatly predominated over the acetyl form whereas after 6- weeks adaptation to a white background the acetylated peptide proved to be the principal component. The results demonstrate that the proteolytic processing of beta-endorphin and the acetylation of alpha-MSH in Xenopus laevis are influenced by background adaptation. The formation of beta-endorphin (1-8) appears to reflect the action of an endopeptidase that acts at the single arginine residue present at position 9.(ABSTRACT TRUNCATED AT 400 WORDS)

In a group of 12 adult Soay rams living outdoors near Edinburgh there was a conspicuous seasonal cycle in the peripheral plasma concentrations of beta-endorphin, ACTH and cortisol. The concentration of all three hormones increased 5- to 20-fold from winter to summer; the seasonal maximum occurring from May to July for ACTH and cortisol and in August for beta-endorphin. At the peak of the cycle the ratio of beta-endorphin to N-acetyl-beta-endorphin was 22:1. The regulation of the seasonal cycle was investigated in a series of five experiments involving treatments with arginine vasopressin (AVP), corticotrophin-releasing factor (CRF) and the synthetic glucocorticoid, dexamethasone. Injection of AVP i.v. induced a dose-dependent increase in the plasma concentration of beta-endorphin (AVP doses of 0, 0.07, 0.33 and 1.67 micrograms/kg). AVP (0.33 micrograms/kg) and CRF (1.67 micrograms/kg) given alone or in combination (equimolar doses), induced an increase in the plasma concentrations of beta-endorphin and ACTH in spring, summer, autumn and winter, and produced a synergistic response when given together. The responses varied with season and were greatest in summer and autumn at the time of the seasonal increase in endogenous secretion. Dexamethasone injected i.v. at 68.04 micrograms/kg produced a decrease in the plasma concentrations of beta-endorphin and ACTH, and the responses were also greatest in summer and autumn. A similar treatment with dexamethasone blocked the AVP-induced increase in the plasma levels of beta-endorphin, indicating an action of dexamethasone on the pituitary gland. Administration of ACTH (0.33 micrograms/kg; i.v.) to rams pretreated with dexamethasone stimulated an increase in the plasma concentration of cortisol; this response varied with season, being greatest in spring at the time of the peak in the seasonal cycle in cortisol secretion. The administration of beta-endorphin (0.33 micrograms/kg) failed to induce an increase in the plasma levels of cortisol at any season. Analysis of the hormone profiles in the control rams based on blood samples collected every 10 min for 8 h revealed pulsatile variations in the plasma concentration of ACTH; some of the spontaneous ACTH peaks were correlated with beta-endorphin peaks. From these results in the Soay ram, we conclude that beta-endorphin and ACTH are co-secreted from the pituitary gland following stimulation by AVP and CRF, and that adrenal glucocorticoids stimulated by ACTH can act in a negative feedback role at the level of the pituitary gland to inhibit the release of both beta-endorphin and ACTH.(ABSTRACT TRUNCATED AT 400 WORDS)