The regulation of gonadotropin release by neurohormones and gonadal steroids in the African catfish, Clarias gariepinus

Abstract

The secretion of gonadotropic hormone (GTH) from the pituitary of teleosts is considered to be regulated by neuropeptides and neuroamines of cerebral origin and steroid hormones from the gonads. This paper reviews our studies concerning the control of GTH release in the African catfish, Clarias gariepinus. It was demonstrated that luteinizing hormone releasing hormone (LHRH) stimulates GTH release and that the gonadotropin release-inhibiting activity of dopamine is restricted to the LHRH-induced GTH release. With regard to the inhibitory action of steroid hormones on GTH release, a hypothesis was postulated which links together the inhibitory actions of dopamines and gonadal steroids. According to this hypothesis, only aromatizable androgens should feed back on the release of GTH and the effects of catecholestrogens and dopamine on GTH release should be comparable.

The effect of pimozide/LHRHa and 17α-hydroxyprogesterone on plasma steroid levels and ovulation in the African catfish, Clarias gariepinus

“…It could be argued that the rise in GTH, caused by the 17a-P injection, may be large enough to explain why this steroid induces ovulation, as well as oocyte maturation, in the African catfish. However, De Leeuw et al (1987) found that a LHRHa treatment usually would not cause ovulation in the African catfish, although the induced GTH levels are much higher than in the present experiment after 17~ P injection.…”

Internal and external factors controlling reproduction in the African catfish,Clarias gariepinus

“…De Leeuw et al (1987), however, did observe an inhibitory effect of catecholestrogens on GTH relcase in catfish, indicating species-spccific differences in GTH regulation by steroids.…”

Sertoli cell proliferation in the adult testis is induced by unilateral gonadectomy in African catfish

“…An initial blood sample was 8 taken from all fish. Anaesthesia and surgery were carried out as described previously [13], except 9 that only one testis was removed. In sham-operated animals, the body wall was opened and closed 10 but both testes were left in place.…”