An investigation on pro-opiomelanocortin and processed peptides from the teleost fish Prochilodus platensis

TRH stimulates the release of POMC-derived peptides from goldfish melanotropes

The release of immunoreactive (ir) alpha-MSH and ir ACTH from goldfish (Carassius auratus) melanotropes was investigated using superfused isolated dispersed neurointermediate lobe cell columns. Stimulation of neurointermediate lobe cell columns with pulses of TRH evoked dose-dependent increases in the concomitant release of ir alpha-MSH and ir ACTH. Reversed-phase high performance liquid chromatography (RP-HPLC) was used to characterize the alpha-MSH and ACTH immunoreactivities released from a neurointermediate cell column under spontaneous release conditions. Six peaks of ir alpha-MSH were revealed. Three of these peaks were identified as des-acetyl alpha-MSH, mono-acetyl alpha-MSH and di-acetyl alpha-MSH. Seven peaks of ir ACTH were revealed. Four of these peaks were tentatively identified as ACTH variants. These studies suggest that TRH stimulates the release of peptide hormones from teleost melanotropes and that the goldfish neurointermediate lobe in vitro releases numerous peptides derived from POMC.

The regulation of the corticomelanotropic cell activity in aves. III--Effect of various peptides on the release of MSH from dispersed, perfused duck pituitary cells. Cosecretion of ACTH with MSH

1. The melanotropin-releasing activity of arginine-vasopressin (AVP), arginine-vasotocin (AVT), oxitocin (OT), mesotocin (MT) and corticotropin-releasing factor (CRF) was studied in the duck using dispersed, perfused pituitary cells and a specific alpha-MSH RIA. 2. Log dose-response curves were obtained for all the peptides ranging from 5 to 100 ng/ml. All peptides behaved as partial agonists compared to duck median eminence extracts (DME). 3. AVT and MT displayed an alpha-MSH releasing capacity of 60% relative to DME whereas all other peptides behaved as weak agonists with less than 15% capacity relative to DME. 4. AVT and CRF when perfused together acted synergistically on alpha-MSH release yielding a dose response line whose slope approximated that of DME. 5. ACTH was cosecreted together with alpha-MSH in all situations studied with an ACTH to alpha-MSH molar ratio of about 10. 6. It is concluded that CRF and neurohypophyseal peptides may be physiological stimulators of both alpha-MSH and ACTH release in aves.

Neuronal localization of immunoreactive adrenocorticotropin-like substance in the hypothalamus of elasmobranch fishes

The occurrence and localization of adrenocorticotropin (ACTH)-like material in the brain of two species of elasmobranch fishes, Scyliorhinus canicula and Squalus acanthias, were studied by immunohistochemical techniques using an antiserum generated against human ACTH1-24. In both species immunopositive neurons and fibers were recognized in the basal hypothalamus mainly distributed in the nucleus lateralis tuberis, in which many of these elements were of the liquor-contacting type. A few ACTH-like positive cells were also found in the nucleus lobi lateralis hypothalami. The features of this peptidergic system, its topographic distribution to form intrinsic circuits within the posterior hypothalamic area and probably connections with the pituitary, suggest implications in brain neuromodulatory activities and hypophyseal regulation for this peptide.

On the stimulatory nature of the control of MSH secretion in ducks

Though birds lack the pars intermedia of the hypophysis, their pituitary glands do secrete MSH. This hormone and ACTH are elaborated in special cells of the pars distalis called corticomelanotrops. The present study was designed to ascertain whether the release of MSH in aves is under either stimulatory or inhibitory hypothalamic control. Extracts of median eminence were injected in ducks and plasma MSH was observed to rise after the injections: on the other hand, when pituitaries were ectopically grafted, significant changes in the levels of circulating MSH were not detected. Twenty days after grafting, the transplants were extirpated and incubated in media containing median eminence extracts. The extracts stimulated the release of MSH not only from grafts but also from pieces of normotopic glands. The grafts showed cells which contained ACTH but not MSH; however, they contained small amounts of MSH, detectable by RIA. The administration of ergocryptine brought about the inhibition of MSH secretion in vivo, and it is suggested that this drug acted on hypothalamic structures rather than directly on the corticomelanotrops. On the basis of the preceding results, it is concluded for the first time that in ducks the release of MSH has stimulatory control from the hypothalamus, contrarily to that occurring in almost all the animals so far investigated.

ACTH-related material in the pituitary gland of the chinook salmon (Oncorhynchus tschawytscha)

The distribution and nature of ACTH-related material in the pituitary gland of chinook salmon (Oncorhynchus tschawytscha) was studied. Pars distalis (PD) and neurointermediate lobe (NIL) extracts were analyzed by gel filtration on BioGel P6 and the resultant fractions assayed for ACTH immunoreactivity (ACTH-IR) using six different antibodies, all of which were specific for ACTH when applied to mammalian samples, and for alpha-MSH. In the PD a number of distinct peaks of ACTH-IR were observed, which were detected to different degrees by the different ACTH antibodies. Three of the ACTH antibodies produced essentially similar results. The other ACTH antibodies produced results quite distinct from these, and distinct from one another. Thus ACTH-IR is present in the salmon PD in a number of distinct forms, all of which appear to have molecular weights between about 2000 and 5000. No alpha-MSH was detected in the PD. All of the ACTH antibodies also detected material in the NIL. In general the different antibodies produced similar results. There were fewer peaks of ACTH-IR in the NIL than in the PD. The major one of these, which eluted between the void volume and 1-39 ACTH, was detected by all the antibodies. One of the antibodies also detected a peak of ACTH-IR which eluted close to where alpha-MSH eluted. All of the ACTH antibodies detected more material in the PD than in the NIL, the ratio being about 3:1 in every case. alpha-MSH-IR eluted as a minor peak at the void volume, and a major peak in the position of authentic 1-13 alpha-MSH.

Lack of glycosilation of pro-opiomelanocortin might account for the periodic acid-Schiff-negative reaction in ACTH cells of teleost fishes

Unlike tetrapod ACTH cells, teleost ACTH cells do not react with the periodic acid-Schiff method (PAS). To find an explanation for this unique feature, chromatographic fractions obtained after filtration of pituitary extracts of Prochilodus platensis in Sephadex were immunologically analyzed. A high-molecular-weight protein which was identified as pro-opiomelanocortin (POMC) was detected. When this POMC was submitted to affinity chromatography in concanavalin binding, it was not detected. Furthermore, pituitaries incubated in media containing [3H]glucosamine or [3H]fucose did not incorporate these amino acids to the newly synthesized POMC. The results obtained strongly suggest an inability of the fish to glycosilate POMC, and this failure could account for the PAS-negative reaction in the ACTH cells.