PLASMA-LEVELS OF OVARIAN-STEROIDS, INCLUDING 17-ALPHA,21-DIHYDROXY-4-PREGNENE-3,20-DIONE AND 3-ALPHA,17-ALPHA,21-TRIHYDROXY-5-BETA-PREGNAN-20-ONE, IN FEMALE PLAICE (PLEURONECTES-PLATESSA) INDUCED TO MATURE WITH HUMAN CHORIONIC-GONADOTROPIN

In one previous paper we reported on the identification of 11-deoxycortisol and 3α,17α,21-trihydroxy-5β-pregnan-20-one in the ovaries and plasma of mature female plaice and also described the development of radioimmunoassays for these two steroids. The present paper describes temporal changes in plasma levels of the free and conjugated forms of these and of some other steroids (17α,20β-dihydroxy-4-pregnen-3-one, 17α,20β,21-trihydroxy-4-pregnen-3-one, 17α,20α-dihydroxy-4-pregnen-3-one, 17α-hydroxy-4-pregnen-one, testosterone, and 17β-oestradiol) in female plaice injected with and without human chorionic gonadotropin (HCG). Oocyte final maturation, but not ovulation, was induced by HCG injections. Levels of most of the steroids were also elevated by the HCG injections and were significantly higher than in control fish throughout the experiment (112 hr). The two most abundant steroids were 11-deoxycortisol and 3α,17α,21-trihydroxy-5β-pregnan-20-one (up to 600 ng ml-1). Only relatively small amounts of 17α-hydroxy-4-pregnene-3,20-dione (<15 ng ml-1), 17α,20β-dihydroxy-4-pregnen-3-one, and 17α,20α-dihydroxy-4-pregnen-3-one (<5 ng ml-1) were found. 17α,20β,21-Trihydroxy-4-pregnen-3-one was not present. Testosterone and 17β-oestradiol levels rose briefly, in response to the first of the two HCG injections, and then fell significantly. The ratio of conjugated to free steroids (except for 17α-hydroxy-4-pregnene-3,20-dione and 17β-oestradiol) was almost always greater than 1. In the HCG-injected fish, there was a significant negative correlation between the response of 17β-oestradiol levels and the response of 11-deoxycortisol and 3α,17α,21-trihydroxy-5β-pregman-20-one levels. This further confirms that, as teleosts approach the time of full maturity, there is switch-over in the ovaries from predominantly C19 and C18 steroid production to predominantly C21 steroid production. © 1990.