Publication Abstract

Plasma steroids in mature common dentex (Dentex dentex stimultated with a gonadottrophin-releasing hormone agonist

L.N. Greenwood, A.P. Scott, E.L.M. Vermeirssen, F. LeGac, C. Mylonas and M. Paulidis

The aim of this study was to identify the major C21 steroids produced in vivo during artificially-induced final oocyte maturation and spawning in female common dentex (Dentex dentex). During the spawning season, mature females were treated with a gonadotropin-releasing hormone agonist (GnRHa)-loaded delivery system, with or without pimozide. Blood samples were collected at various intervals during the experiment and were assayed for GnRHa; 17,20β-dihydroxy-4-pregnen-3-one (17,20β-P) and 17,20β,21-trihydroxy-4-pregnen-3-one (17,20β,21-P). A higher percentage of ovulated females was observed in GnRHa implanted fish, which produced more than 10-fold greater numbers of eggs than controls. Plasma concentrations of 17,20β-P were higher between 2 and 10 days after treatment. Pimozide had no discernible effect on egg production or plasma steroid concentrations. In another experiment, ovulating common dentex were injected intramuscularly with a single dose of 50 µg kg^-1 of GnRHa in saline and were sampled for blood at 0, 3, 6, 12 and 24 h post injection. A single water sample was taken from the tanks at 9 h post injection, the tanks having been emptied and refilled at 6 h. Measurements were made of plasma and water concentrations of free and conjugated 17,20β-P, 17,20β,21-P, 17β-oestradiol (E2) and GnRHa (plasma only). The GnRHa injection increased plasma levels of all steroids, with free 17,20β-P reaching maximal levels within 3 h. GnRHa treatment also increased the amounts of free and conjugated steroids released into the water between 6 and 9 h.

Reference:

L.N. Greenwood, A.P. Scott, E.L.M. Vermeirssen, F. LeGac, C. Mylonas and M. Paulidis, 2001. Plasma steroids in mature common dentex (Dentex dentex stimultated with a gonadottrophin-releasing hormone agonist. General and Comparative Endocrinology , 123(1): 1-12