Effect of epidermal growth factor on reproductive function of ewes

Adult Merino ewes were infused via the jugular vein with either saline (n = 5) or epidermal growth factor (EGF) (4.2 micrograms/kg per h, n = 6) for 24 h in either the luteal phase or the follicular phase of the oestrous cycle and reproductive function was examined. Infusion of EGF during the luteal phase caused no detectable change in plasma progesterone or prolactin concentrations over a 7-day period compared with the controls. Infusion of EGF during the follicular phase suppressed the oestrous rise in plasma oestradiol. Luteinizing hormone pulse amplitude was increased and pulse frequency was decreased by the end of the infusion. All control ewes had a pro-oestrous LH surge and mated, but the LH surge and oestrus were prevented by EGF infusion. Nevertheless, plasma progesterone levels rose subsequently in the EGF-infused ewes in parallel with the control ewes, suggesting that the preovulatory follicle had luteinized. Both LH and FSH rose over the 7 days after EGF infusion to levels similar to those in ovariectomized ewes. Thus EGF appears to inhibit follicular oestradiol production, although it does not affect luteal progesterone production or follicular luteinization. We suggest that the alteration in gonadotrophin secretion patterns results from a disturbance of feedback mechanisms between the ovary and the hypothalamopituitary axis, although a direct effect in the brain or the pituitary gland cannot yet be excluded.