CONJUGATES OF OVARIAN STEROIDS, INCLUDING 17α, 20β-DIHYDROXY-4-PREGNEN-3-ONE (MATURATION-INDUCING STEROID), ACCUMULATE IN THE URINE OF A MARINE TELEOST (PLAICE; PLEURONECTES PLATESSA)

Abstract

ABSTRACT Free and conjugated 17α, 20β-dihydroxy-4-pregnen-3-one (17, 20β-P), 17α, 21-dihydroxy-4-pregnene-3, 20-dione (11-deoxycortisol) and 3α, 17α, 21-trihydroxy-5β-pregnan-20-one (3α, 17, 21-P-5β) were measured by radioimmunoassay in matching blood plasma and urine samples from plaice (Pleuronectes platessa) females at several ovarian maturity stages: post-vitellogenesis (IV), final oocyte maturation (V), and ovulation (VI). Free steroids were generally low in all samples. Conjugated steroids were up to 2 orders of magnitude higher in urine than in plasma samples. Conjugated 17, 20β-P was higher in stage V than in stage IV or VI females. Conjugated 11-deoxycortisol was higher in stage IV and V females. Conjugated 3α, 17, 21-P-5β was higher in stage V and VI females. These results support earlier studies which indicated that 17, 20β-P was the most likely maturation-inducing steroid (MIS) in plaice, and that the urine might be a vehicle for steroid pheromones synthesized by the gonads.