Plasma-Sulfated C21-Steroids Increase during the Periovulatory Period in Female Common Wolffish and Are Influenced by Temperature during Vitellogenesis

Abstract

Plasma concentrations of steroids during the periovulatory period were measured in female common wolffish reared at three different temperatures. Steroids were quantified by radioimmunoassay (RIA). Two “broad-spectrum specificity” RIAs—one which detects C21-steroids with a 17,20β-dihydroxyl configuration (17,20β-steroids) and the other which detects C21-steroids with a 5β-reduced, 3α-hydroxyl configuration (5β,3α-steroids)—picked up very large amounts of cross-reacting material (1.7 μg ml−1 in one fish) in the sulfate fraction of plasma from ovulating females. Reverse-phase high-performance liquid chromatography and thin-layer chromatography revealed two major steroids: 5β-pregnane-3α,17,20β-triol (80%) and 5β-pregnane-3β,17,20β-triol (20%). The sulfated forms of these steroids were elevated 4 to 6 days before and during ovulation, compared with those of females in vitellogenic and postspawning condition, in which concentrations were below 2.0 ng ml−1. In the three groups of fish held at 4, 8, and 12°C during vitellogenesis, but returned to 4°C just prior to the spawning season, the mean concentrations of sulfated 17,20β-steroids in ovulating females were 530, 635, and 325 ng ml−1, respectively. The corresponding concentrations of free 17,20β-dihydroxy-4-pregnen-3-one (17,20β-P; the maturation-inducing steroid in many teleosts) were 0.88, 0.86, and 0.57 ng ml−1, respectively. Only minute amounts of 17,20β,21-P and its sulfated derivatives were detected. Significantly lower steroid concentrations in the 12°C group indicate that steroid synthesis and/or metabolism during the periovulatory period are influenced by the temperature experienced during vitellogenesis. In male fish, plasma concentrations of both sulfated 17,20β-steroids and free 17,20β-P were low (<2.0 ng ml−1) at all times.