Effect of thyroxine, prolactin and adrenalin on the gravid ovaries of the frog Rana cyanophlyctis (Schn.).

The effects of thyroxine, prolactin and adrenalin on the gravid ovaries of R. cyanophlyctis were studied during late prebreeding period when vitellogenic growth of oocytes is complete or near completion. Specified doses of hormones were injected (ip) six days a week for one month. They were fed guppies ad libitum daily 6 days a week. Administration of 2 or 5 micrograms eltroxine (synthetic thyroxine) had no effect on ovaries or oviducts. Whereas, higher doses 8, 12 and 16 micrograms thyroxine caused significant (P < 0.05) decrease in the per cent weight of ovaries and oviducts. The mean diameter of the largest oocyte was also reduced significantly compared to the controls. There was an increase in the atresia of vitellogenic oocytes. Treatment with 100 micrograms prolactin also caused reduction in the per cent weight of ovaries and oviducts. However, mean diameter of the largest oocyte did not change significantly. Follicular atresia increased only moderately. Injection of 180 micrograms adrenalin bitartrate caused drastic decrease (P < 0.05) in the per cent weight of ovaries and oviducts and mean diameter of the largest oocyte. Many yolky follicles became atretic. The findings suggest that increase in the levels of thyroxine (beyond a certain limit), prolactin and adrenalin around the breeding period decrease the fecundity of the frog by inducing atresia of yolky oocytes. We conclude that the above hormones in excess quantities act as negative modifiers of ovarian activity in R. cyanophlyctis.