The effects of exogenous growth hormone on follicular steroid secretion and ovulation rate in sheep

Growth hormone (GH) has diverse actions in many tissues, including the foll icle. This paper summarizes three experiments that examined the effects of GH and insulin-like growth factor (IGF)-I on the ovary. Ewes given oGH and pregnant mane serum gonadotrophin were compared with control and pregnant m ane serum gonadotrophin-treated ewes. Ewes, with synchronized cycles, were given varying doses of pregnant mane serum gonadotrophin and/or oGH to dete rmine if oGH is able to augment ovulation rate (Experiment 1). Experiments 2 and 3 used the ovarian autotransplant model. Ewes were infused via the ov arian artery with oGH (Experiment 2) or insulin-like growth factor I (IGF-I ) (Experiment 3). Both were administered for 12 hr on Day 10. In Experiment 2, ewes were given intravenous gonadotropin releasing hormone (150 ng iv) at -2.5 and 10.5 hr relative to infusion. Ovarian and jugular venous blood was collected every 15 min from -30 to 150 min relative to gonadotropin rel easing hormone. In Experiment 3, luteolysis was induced at the end of infus ion. Ovarian and jugular venous blood was collected every 3 hr from before and until 84 hr after the infusion. Estradiol and androstenedione were assa yed in ovarian venous plasma and GH in jugular venous plasma. In Experiment 1, treatment with oGH increased the jugular venous concentration of GH. Ho wever, in Experiment 2 treatment with oGH via the ovarian artery did not in crease jugular venous GH but did increase ovarian venous GH. Treatment with oGH had no effect on ovulation rate (Experiment 1) or the secretion of and rostenedione and estradiol (Experiment 2). Infusion of IGF-I (Experiment 3) increased the secretion of estradiol during the follicular phase. These da ta show that short-term treatment of sheep with GH had no in vivo effects o n the follicle and that IGF-I was a potent stimulator of follicular steroid ogenesis in vivo. (C) 1999 Elsevier Science Inc. All rights reserved.