Ovulation rate and the concentrations of gonadotrophins and metabolic hormones in ewes infused with glucose during the late luteal phase of the oestrous cycle

The positive relationship between nutrition and ovulation rate was investigated in sheep infused intravenously with glucose. Ovulation rate increased (2.0 ± 0.0 vs 2.4 ± 0.3) when ewes were given an infusion of glucose (60-65 mM/h) for five days in the late luteal phase of the oestrous cycle. The effect of glucose was obtained without any significant change in LH secretion. The concentration of FSH in glucose-infused ewes was lower during the infusion (luteal phase) but higher during the early follicular phase. These data suggest that the change in ovulation rate occurred without increased gonadotrophin support to the follicle during the late luteal phase, which is the period of the sheep oestrous cycle during which improved nutrition increases ovulation rate. There were no changes in GH or prolactin, but changes in circulating glucose and insulin levels were detected. We conclude that insulin, because of its role in cell growth and metabolism, is involved in mediating ovulation responses to nutritional stimuli, either directly or more likely by the stimulation of insulin-mediated glucose uptake.