Circulating C-21 steroids in relation to reproductive condition of a viviparous marine teleost, Sebastes rastrelliger (grass rockfish)

Plasma concentrations of free, glucuronidated, and sulfated steroids were m easured in grass rockfish (Sebastes rastrelliger) at identified stages of o varian development and pregnancy using radioimmunoassays validated for the detection of individual steroids or compounds with a particular configurati on. Changes in reproductive status were most clearly reflected in concentra tions of free C-21 steroids. Previtellogenic, vitellogenic, and postspawn f ish exhibited uniformly low concentrations of circulating C-21 steroids whi le pregnant fish showed a pronounced and significant increase in a series o f free 17,20 beta-dihydroxylated steroids together with 17,20 alpha-P. Amon g individual steroids, the compound exhibiting the greatest fluctuation in relation to reproductive condition was 17,20 beta-P-5 beta, which during pr egnancy showed a 22-fold increase from basal concentrations. Smaller relati ve increases in association with pregnancy were also seen in 17,20 beta-P, 17,20 beta,21-P, and 17,20 alpha-P (3.5-, 3.5-, and 5.5-fold increases, res pectively). Fish in the final stages of pregnancy or which had recently spa wned exhibited uniformly low concentrations of the C-21 steroids, indicatin g a drop in circulating amounts of these compounds around the time of partu rition. The hormone profiles established during the annual reproductive cyc le of the grass rockfish suggest that C-21 steroids may contribute to the e ndocrine mechanisms which regulate viviparity in this highly fecund marine teleost. The C-21 steroids characterized in this study may pro,ide appropri ate reference compounds in the future evaluation of this concept. (C) 2000 Academic Press.