Submitted to: Animal Reproduction Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/30/2000
Publication Date: 11/20/2000
Citation: Ford, J.J., Berardinelli, J.G., Christenson, R.K., Anderson, L.L. 2000. Luteinizing hormone secretion as affected by hypophyseal stalk transection and estradiol-17beta in ovariectomized gilts. Animal Reproduction Sciences. 63(3-4):255-274. Interpretive Summary: These studies investigated the effect of estradiol regulation of luteinizing hormone (LH) secretion in female pigs. The animal model was ovariectomized female that were subsequently hypophyseal stalk transected. The conclusion was the estradiol is incapable of increasing LH secretion through direct effects on the anterior pituitary gland. These findings will assist other investigators in the resolution of subsequent questions.
Technical Abstract: The objectives were to determine hypothalamic regulation of pulsatile luteinizing hormone (LH) secretion in female pigs and the biphasic feedback actions of E2-17beta. Ovariectomized gilts were assigned to treatments: hypophyseal stalk transection (HST) or unoperated control (UOC). Pulsatile LH secretion, 2 days after ovariectomy, exhibited a frequency of 0.9 peaks/h, amplitude of 1.3 ng/ml, baseline of 0.8. In HST gilts pulsatile LH release was abolished and mean LH concentration decreased. In UOC gilts, E2-17beta induced a 60% decrease in LH concentration within 12 h, and LH remained low until 48 h, then increased to peak values by 72 h, and was followed by a gradual decline to 120 h. Pituitary weight decreased 31% in HST gilts compared with controls (228 vs. 332 mg, P < 0.05), but normal basophils were evident in the adenohypophysis of HST gilts. A second study determined that hourly iv infusion of LHRH (2 ug) and a second injection of E2- 17beta 48h after the first had no effect on the positive feedback action of estrogen in UOC. But, in HST gilts that received LHRH hourly, the first injection of E2-17beta decreased plasma LH concentrations; however, the second injection of E2-17beta failed to induce a positive response to estrogen. These results indicate that the isolated pituitary of HST gilts is capable of autonomous secretion of LH, E2-17beta will elicit direct negative feedback action on the isolated pituitary gland when supported by exogenous LHRH, but E2-17beta at high concentrations will not induce positive feedback.