Opioid and 17β-estradiol regulation of LH and FSH secretion during sexual maturation in heifers

Abstract

The objective of the present study was to examine the involvement of opioid neuropeptides and E 2 in regulating circulating concentrations of gonadotropins during sexual maturation in the bovine female. Prepubertal (immature) and postpubertal (mature) bovine females were used. Mean concentrations of luteinizing hormone (LH) and follicle- stimulating hormone (FSH) in circulation before and after administration of naloxone were determined in ovariectomized heifers administered E 2 and ovariectomized heifers not administered E 2. A linear decline (P<0.01) in opioid suppression of LH and FSH occurred during the experimental period in immature heifers receiving E 2. This decline in opioid suppression of LH and FSH occurred during the same period of time that intact control heifers were initiating estrous cycles at puberty. Little change of opioid suppression of LH and FSH occurred during the experimental period in immature heifers not receiving E 2 and mature heifers receiving E 2. Our research indicates that opioid neuropeptides and E 2 act together to regulate LH and FSH secretion during sexual maturation in the bovine female.