Effects of sex steroids on the mRNA levels of gonadotropin subunits in juvenile and ovariectomized goldfish Carassius auratus

In order to elucidate the regulation of gonadotropin (GTH) gene expression by gonadal sex steroids, the effects of ovariectomy and sex steroid adminis tration on pituitary mRNA levels of GTH subunits were examined in goldfish. Ovariectomy caused a marked increase in GTH 1 beta mRNA levels, and steroi d hormone replacement (testosterone, T; estradiol-17 beta, E-2; and 11-keto testosterone, KT) suppressed the elevated levels in sexually early recrudes cent and mature females. Pituitary mRNA levels of alpha and GTH 11 beta wer e not affected by ovariectomy and steroid hormone treatment. When sex stero ids (T, E-2, and KT) were administered to sexually immature juvenile fish, GTH 1 beta mRNA levels were suppressed as observed in adult fish. However, GTH 11 beta mRNA levels were observed to increase by sex steroids (T and E- 2 but not KT) unlike that observed with adult fish. These results indicate that sex steroids exert an inhibitory effect on GTH Ip mRNA levels from the time goldfish are immature to the time they are mature. However, sex stero ids (T and E-2) have a stimulatory effect on GTH 11 beta mRNA levels in juv enile goldfish and the effect becomes less pronounced when they become adul t.