Effect of dexamethasone and ACTH on oocyte growth and recruitment in the frog Rana cyanophylyctis during the prebreeding vitellogenic phase

Abstract

The effects of 5, 25, 50 and 75 μg of dexamethasone and 0.1 or 0.5 IU ACTH on oocyte growth and recruitment were studied in Rana cyanophlyctis during prebreeding vitellogenic phase (May). Injections (ip) were given 6 days a week for 31 days and frogs were killed on the 32nd day. Treatment with 5 μg dexamethasone had no effect on gonadosomatic index (GSI) or on the number and percentage of different oocytes. Administration of 25 μg dexamethasone caused a significant ( P < 0.05) increase in both number and percentage of medium second growth phase (MSGP) oocytes and atretic follicles (AF), and a numerical reduction in number and percentage of large second growth phase (LSGP) oocytes. Frogs which received 50 or 75 μg dexamethasone exhibited a significant ( P < 0.05) decrease in GSI, ovarian weight, and number and percentage of LSGP oocytes, while those of MSGP oocytes and AF increased. There was no effect of dexamethasone on first growth phase (FGP) oocytes. The administration of 0.1 IU ACTH had no effect on GSI, percentage of different oocytes, or MSGP and LSGP number. There was a numerical increase in number of FGP oocytes. Treatment with 0.5 IU ACTH caused a significant ( P < 0.05) decrease in GSI, ovary weight, and number and percentage of LSGP oocytes, while those of AF increased. The above findings suggest that lower doses of dexamethasone (5 or 25 μg) and of ACTH (0.1 IU) have no effect on oocyte recruitment and growth, but that higher doses (50 or 75 μg dexamethasone and 0.5 IU ACTH) impair vitellogenic growth of oocytes and increase follicular atresia. Further, they suggest that glucocorticoids act as negative effectors on ovarian growth in R. cyanophylyctis during the prebreeding vitellogenic phase.