IN-VIVO REGULATION OF THE STEROIDOGENIC ACTIVITY OF RAT LUTEAL CELLS BY INSULIN

The aim of the present study was to determine the long-term effects of insulin treatment on luteal cell function. For this purpose, superovu lated prepubertal rats were treated with insulin (group I) or vehicle (group C) for 9 days. Serum progesterone (P-4) levels were increased i n the insulin-treated group (55 +/- 10 vs 134 +/- 31 ng/ml, P < 0.05). Isolated luteal cells were incubated 3 h, and P-4 and 20 alpha-hydrox y-progesterone (20 alpha-OH-P) were measured in the incubation media. A decrease in P-4 levels and an increase in 20 alpha-OH-P values [P-4 (ng/ml): C = 26.6 +/- 0.3; I = 20 +/- 2; 20 alpha-OH-P (ng/ml): C = 62 +/- 2; I: 120 +/- 7; P < 0.01] were observed in group I. In addition, progestagen (P-4 + 20 alpha-OH-P) levels were higher in group I (C = 88 +/- 2; I = 140 +/- 9 ng/ml; P < 0.001). When cytochrome P450(scc) c ontents were measured by immunoblotting, a marked increase was observe d in luteal cells obtained from group I. LH receptor numbers were decr eased in luteal cells isolated from group I (C = 388,834 +/- 14,146; I = 303,057 +/- 13,392 sites/cell; P < 0.001) with a concomitantly dimi nished LH responsiveness. It is concluded that in vivo treatment of su perovulated rats with insulin increases luteal progestagen production by increasing the content of cytochrome P450(scc).