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 measured in grass rockfish (Sebastes rastrelliger) at identified stages of ovarian development and pregnancy using radioimmunoassays validated for the detection of individual steroids or compounds with a particular configuration. Changes in reproductive status were most clearly reflected in concentrations of free C-21 steroids. Previtellogenic, vitellogenic, and postspawn fish exhibited uniformly low concentrations of circulating C-21 steroids while pregnant fish showed a pronounced and significant increase in a series of free 17,20beta-dihydroxylated steroids together with 17,20alpha-P. Among individual steroids, the compound exhibiting the greatest fluctuation in relation to reproductive condition was 17,20beta-P-5beta, which during pregnancy showed a 22-fold increase from basal concentrations. Smaller relative increases in association with pregnancy were also seen in 17, 20beta-P, 17,20beta,21-P, and 17,20alpha-P (3.5-, 3.5-, and 5.5-fold increases, respectively). Fish in the final stages of pregnancy or which had recently spawned exhibited uniformly low concentrations of the C-21 steroids, indicating a drop in circulating amounts of these compounds around the time of parturition. The hormone profiles established during the annual reproductive cycle of the grass rockfish suggest that C-21 steroids may contribute to the endocrine mechanisms which regulate viviparity in this highly fecund marine teleost. The C-21 steroids characterized in this study may provide appropriate reference compounds in the future evaluation of this concept.