Radioimmunoassay for gamma-endorphin

Immunocytochemical evidence for intragranular processing of pro-opiomelanocortin in the melanotropic cells of the rabbit

The immunogold technique, employing antisera with clear-cut specificities, was used to localise different processing stages of pro-opiomelanocortin (POMC) in rabbit melanotropic cells. While the antiserum against gamma 3-MSH labelled all the secretory granules including intrasaccular condensations in the Golgi apparatus, antisera against alpha-MSH only labelled extra-Golgi secretory vesicles (SV). All extra-Golgi SV were likewise labelled with the three antisera against alpha-MSH used, despite their different specificities for the deacetylated, N-acetylated or C-amidated forms of the peptide. The antibody against beta-endorphin also labelled the extra-Golgi SV, while only some SV were labelled with the antibody against gamma-endorphin. These results correlate with biochemical data in favour of mainly--if not exclusively--intragranular processing of POMC. Except for gamma 3-MSH, the cleavage of which could coincide with Golgi packaging of secretory material, other post-translational modifications of the precursor seem to occur when SV are discharged outside the Golgi area. The cleavage of gamma-endorphin appears to be a later step in POMC processing, occurring in some mature SV.

Isolation and characterization of alpha-endorphin and gamma-endorphin from single human pituitary glands

alpha-Endorphin and gamma-endorphin, two closely related peptides of the pro-opiomelanocortin family with characteristic biological activities, were purified to homogeneity from single human pituitary glands and chemically identified. Isolation of the peptides was based on size fractionation by Sephadex G-75 chromatography followed by two HPLC steps using reverse-phase and paired-ion reverse-phase systems and was monitored by radioimmunoassay. During the isolation procedure alpha- and gamma-endorphin-sized material behaved chromatographically and immunologically indistinguishably from synthetic alpha- and gamma-endorphin. The amino acid composition and NH2-terminus of isolated peptides demonstrated their identity as authentic alpha-endorphin and gamma-endorphin. Acetylated forms were absent. In addition, evidence is provided that large forms with alpha- and gamma-endorphin immunoreactivity detected during gel filtration are human lipotropin-(1-74) and -(1-75), respectively. The data substantiate that alpha-endorphin and gamma-endorphin exist as endogenous peptides in the human pituitary gland.

In vitro study of frog (Rana ridibunda Pallas) neurointermediate lobe secretion by use of a simplified perifusion system. III. Effect of neuropeptides on alpha-MSH secretion

It has been previously demonstrated that thyrotropin-releasing hormone (TRH) stimulates in vitro the release of alpha-melanocyte-stimulating hormone (alpha-MSH) in frog. In the present study, the effects of various neuropeptides on spontaneous and/or TRH-induced alpha-MSH secretion were investigated, using a well-defined perifusion system technique. Vasoactive intestinal peptide, (VIP) a neurohormone which stimulates TRH target cells in mammals, was totally devoid of effect on frog melanotrophs although VIP-like material could be detected in neurointermediate lobe extracts. Somatostatin-like immunoreactive material was found in high concentrations in the frog neurointermediate lobe complex, but synthetic somatostatin (from 10(-10) to 10(-6) M) did not modify the spontaneous release of alpha-MSH. At doses of 10(-8) and 10(-6) M, synthetic somatostatin did not modify TRH-induced alpha-MSH secretion. Morphine (10(-5) M) and opioid peptides (10(-10) to 10(-6) M) had no effect on spontaneous alpha-MSH secretion. In addition, methionine enkephalin (10(-5) M) did not modify the stimulatory effect of TRH on alpha-MSH secretion. From these results we conclude that, among the neuropeptides which modulate prolactin secretion in mammals, only TRH is involved in alpha-MSH secretion in the frog.

Immunological characterization of endorphins, adrenocorticotropin, and melanotropins in frog hypothalamus

To gain more information about the nature and regulation of opiomelanocorticotropic peptides in the frog diencephalon, radioimmunological determinations of alpha- and beta-MSH. ACTH, beta- and gamma-endorphins have been performed in hypothalamic extracts. Sephadex G-50 gel filtration revealed a single peak of alpha-MSH-like immunoreactivity (alpha-MSH-LI) comigrating with synthetic alpha-MSH. Two peaks of ACTH-LI were observed; the major one eluting slightly before human ACTH. Using a porcine beta-endorphin antiserum which exhibited 45% cross-reaction (on a molar basis) with ovine beta-LPH, one major peak of beta-endorphin-LI and two additional components were observed in the elution profile; none of these peaks coeluted with synthetic porcine beta-endorphin. No significant beta-MSH or gamma-endorphin-LI was detected. To investigate a possible role of glucocorticoids on the level of opiomelanocorticotropic peptides in frog hypothalamus, 60 male frogs were treated with dexamethasone (300 micrograms/day) during 8 days. Dexamethasone treatment did not modify the chromatographic distribution and the total amount of alpha-MSH-LI and ACTH-LI in hypothalamic extracts. A slight (15%) increase in beta-endorphin-LI was even observed after 8 days of dexamethasone treatment. From these results it is concluded that three classes of opiomelanocorticotropic peptides are present in the frog hypothalamus in the following order of concentration: beta-endorphin-LI greater than alpha-MSH greater than ACTH. In addition, circulating glucocorticoids which significantly reduce the concentration of opiomelanocorticotropic hormones in the distal lobe of the frog pituitary (S. Jégou, M. C. Tonon, F. Leboulenger, C. Delarue, J. Côté, G. Pelletier, and H. Vaudry (1981a). In "Adv. Physiol. Sci.' E. Stark, G. B. Makara, Zs. Acs, and E. Endröczi, eds., Vol. 13, pp. 129-133. Pergamon, Budapest.) do not modify the amount of these peptides in the hypothalamus.

Immunocytochemical evidence of intragranular acetylation of alpha-MSH in the melanotrophic cells of the rabbit

Melanotrophic cells of the pars intermedia of the rabbit were studied at the electron-microscopic level by means of the immuno-gold technique with the use of antisera against gamma 3-MSH and alpha-MSH. Both antibodies labelled all secretory vesicles stored in the peripheral cytoplasm, but secretory vesicles and intrasaccular condensations in the Golgi area reacting for gamma 3-MSH were not labelled with the antibody against alpha-MSH. Since this antibody appears to recognise only the acetylated form of alpha-MSH, the present observations suggest that acetylation occurs at a stage subsequent to the Golgi packaging, during maturation of the secretory vesicles. Thus, the morphological evidence supports biochemical data in favour of intragranular processing of opiomelanocortin in melanotrophic cells.

Biosynthesis of pairs of peptides related to melanotropin, corticotropin and endorphin in the pars intermedia of the amphibian pituitary gland

This study concerns the biosynthesis of a number of peptides in the neurointermediate lobe of the pituitary gland of the aquatic toad, Xenopus laevis. Using pulse-chase incubations in vitro and high-performance liquid chromatographic analysis, it could be shown that these peptides are synthesized through processing of a prohormone, pro-opiomelanocortin; all peptides were released into the incubation medium. On the basis of electrophoretic analysis, selective amino acid incorporation and immunoprecipitation, as well as peptide mapping by high-performance liquid chromatography, the peptides were classified into three distinct groups: two related to melanocyte-stimulating hormone (melanotropin), two related to adrenocorticotropic hormone (corticotropin) and two endorphin-like peptides. Using tryptic and chymotryptic maps of synthetic alpha-melanotropin and des-Ac alpha N-alpha-melanotropin as references, one of the melanotropin-like peptides was identified as des-Ac alpha N-alpha-melanotropin; the other one represents neither alpha-melanotropin nor any other known melanotropic peptide. The two peptides that were immunologically related to corticotropin had characteristics consistent with a structures resembling a peptide previously named 'corticotropin-like intermediate lobe peptide', corticotropin-(18-39). The two endorphin-like peptides, although highly related, do not have the same primary structure. In view of the apparent structural differences between the two peptides in each group, the possible occurrence of two prohormones is discussed.

High yield coupling of peptides to protein carriers

Coupling of peptides to protein carriers has been achieved at a high level of peptide incorporation. Bovine serum albumin was used as the model carrier protein and several peptides were tested in the coupling reaction. The peptides were coupled to succinylated bovine serum albumin after conversion of its carboxyl side chains to the reactive p-nitrophenyl ester group by reaction with p-nitrophenol/N,N'-dicyclohexylcarbodiimide in anhydrous dimethylformamide. The reaction afforded succinyl-albumin-peptide conjugates that had high level of peptide incorporation (18-35 mol peptide/mol albumin). In addition to the high level of peptide coupling, the reaction avoids the production of polymeric forms of peptide, protein or conjugate.

Regional distribution of gamma- and beta-endorphin-like peptides in the pituitary and brain of the rat

Sensitive and specific radioimmunoassays for gamma- and beta-endorphin-like peptides (gamma E and beta E) were used to examine the distribution and relationship of these peptides in the pituitary and in microdissected nuclear brain areas of the male rat. In the pituitary, the highest amounts of gamma E and beta E were found in the neurointermediate region of the gland. On a molar basis, gamma E-like immunoreactivity was found to exist as a relatively constant proportion of beta E-like peptides throughout the pituitary. In the brain, while beta E-like peptides were detected in many brain areas, gamma E-like peptides were detected in only a limited number of sites. In most of these areas, the molar ratio of gamma E to beta E-like peptides closely approximated that found in the pituitary. However, in the ventromedial nucleus of the hypothalamus and nucleus accumbens a higher proportion of gamma E to beta E was measured. These results suggest preferential formation of gamma E or related peptides in certain areas of the brain may occur.