Gonadotrophin-releasing hormone agonist stimulates milt fluidity and plasma concentrations of 17,20β-dihydroxylated and 5β-reduced, 3α- hydroxylated C21 steroids in male plaice (Pleuronectes platessa)

TitleGonadotrophin-releasing hormone agonist stimulates milt fluidity and plasma concentrations of 17,20β-dihydroxylated and 5β-reduced, 3α- hydroxylated C21 steroids in male plaice (Pleuronectes platessa)
Publication TypeJournal Article
Year of Publication1998
AuthorsVermeirssen, ELM, Scott AP, Mylonas CC, Zohar Y
JournalGeneral and Comparative Endocrinology
Volume112
Issue2
Pages163 - 177
Abstract

Spermiating male plaice were caught in the North Sea and acclimatised to laboratory conditions. In two experiments, males were injected intramuscularly with either microspheres or pellets containing gonadotrophin- releasing hormone agonist (GnRHa). Blood was sampled at 2- to 5-day intervals. Individual blood plasma specimens were assayed for testosterone, 5β-reduced, 3α-hydroxy ('5β,3α') steroids and sulphated 17,20βdihydroxy ('17,20β') steroids. Pooled plasma samples were also assayed for free and sulphated 17,20β-dihydroxy-4-pregnen-3-one, free 11-ketotestosterone, and glucuronidated testosterone and 11-ketotestosterone. Plasma concentrations of all steroids were significantly elevated by GnRHa from 2 to 5 days onwards following treatment. The most marked changes occurred in the concentrations of the sulphated 17,20β steroids, which comprised approximately equal amounts of 5β-pregnane-3α, 17,20β-triol 20-sulphate (3α,17,20β-P-5β-S) and 5β-pregnane-3β,17,20β-triol 20-sulphate, rising from ca. 1 to 30-80 ng/ml in the first and from ca. 8 to 80 ng/ml in the second experiment. Concentrations of 511,3α steroids matched those of 17,20β steroids in one experiment. However, in the other experiment, the two RIAs yielded highly disparate results in about 50% of the fish (including males in the control group). The plasma of these fish contained excessive amounts of 5β,3α- immunoreactive material between 10 and 25 days. This material was identified as 3α,17,21-trihydroxy-5β-pregnan-20-one 21-sulphate (a metabolite of 11- deoxycortisol). All previous studies have indicated that when plasma concentrations of this steroid are high, so are those of 3α,17,20β-P-5β- S. This is the first indication that these steroids are regulated independently. In a third experiment, milt fluidity and production were assessed at 10, 15, and 25 days following GnRHa implantation. Milt volume and fluidity were significantly enhanced by the GnRHa treatment.

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