The effect of a direct arterial infusion of insulin and glucose on the ovarian secretion rates of androstenedione and oestradiol in ewes with an autotransplanted ovary

Improving ewe nutrition even for short periods will increase ovulation rate . The increased nutrients must in some way affect the number of follicles t hat develop to the pre-ovulatory stage. One possible mechanism is that a nu trient or a metabolic hormone that responds to nutrition might act directly on the ovary to influence follicle development and/or follicle selection. In the study described here, insulin and glucose, alone or together, were i nfused directly into the ovarian artery of ewes with an autotransplanted ov ary, for 13.5 h on day 11 of the oestrous cycle. The pattern of androstened ione and oestradiol secretion in response to a GnRH-stimulated LH pulse was measured 2.5 h before and 12.5 h and 24.5 h after the start of the infusio n. Glucose or insulin infused alone had no effect on the secretion of andro stenedione and oestradiol. However, when infused together, they decreased s ignificantly the secretion of androstenedione and, to a lesser extent, oest radiol. We suggest that the sudden availability of additional glucose and i nsulin increases insulin-stimulated glucose uptake by the follicle. This le ads to an inhibition of LH-stimulated steroidogenesis by the ovarian follic le which occurs in the absence of any detectable changes in circulating pla sma concentrations of FSH. These results show that insulin and glucose act together to influence ovarian function directly and suggest that the effect s of short-term nutrition on ovulation rate may be mediated by a direct ova rian action of insulin and glucose.