PLASMA CONCENTRATIONS OF LUTEINIZING HORMONE, FOLLICLE STIMULATING HORMONE AND PROLACTIN IN OVARIECTOMIZED, HYSTERECTOMIZED AND INTACT SWINE

Abstract

In order to critically evaluate the temporal patterns of plasma luteinizing hormone (LH), follicle stimulating hormone (FSH) and prolactin (PRL); blood samples were collected daily at 0600, 1200, 1800 and 2400 hrs from intact, sham, ovariectomized and hysterectomized Yorkshire sows via indwelling vena caval cannulae. The maximum preovulatory plasma LH concentration in the intact and sham operated swine (mean ±l SD, 7.06±2.40 ng/ml) was reached between 2400 hrs on the first day of estrus (day 0) and 0600 hrs on day 1. Preovulatory LH peaks averaged 28.75±4.76 hrs duration from initial rise from, and return to, a baseline concentration of 1.19±.25 ng/ml plasma. In addition to the preovulatory LH peak, an average of 8.75 luteal phase peaks was observed during each estrous cycle . Approximately 69.5% ·of the luteal phase peaks had an average duration of 12.65±1.79 hrs, an average maximum plasma concentration of 2.29±.55 ng/ml and occurred during days 2 to 17. The remaining luteal phase peaks reached a maximum concentration of 2.86±1.04 ng/ml and occurred during days 2 to 13. The average duration of these luteal phase peaks was 18.61± 3.49 hrs. The largest and most consistent plasma FSH peak in the intact and sham operated swine occurred between days 2 and 3. This postovulatory peak had a duration of 58.17±16.25 hrs and reached an average maximum concentration of 13.14±9.42 ng/ml before returning to a baseline of 4.76± 1.56 ng/ml plasma. The initial rise of the postovulatory FSH peak coincided with the initial rise of the preovulatory LH peak, but did not reach maximum concentration until 2.66±.45 days after the preovulatory LH peak had reached maximum concentration. In some animals, a luteal phase FSH peak occurred between days 8 to 14. The luteal phase FSH peaks had a duration of 18.09±5.36 hrs and an average maximum concentration of 9.76± 3.78 ng/ml plasma. An average of 2.58±1.08 plasma PRL peaks was observed between day 0 and day 2 of the estrous cycle in the intact and sham operated swine. These peaks averaged 20.54±4.02 hrs in duration and reached maximum concentrations of 11.49±2.97 ng/ml before returning to a baseline of 6.54± 1.29 ng/ml plasma. They reached their maximum concentration approximately 9.12±9.84 hrs after the maximum concentration of the preovulatory LH peak had been reached. Larger prolactin peaks occurred during the follicular phase of the estrous cycle. An average of 3.09±1.38 peaks occurred between days 14 and 19.· These peaks had an average duration of 18.98±3.30 hrs and reached a maximum concentration of 14.28±4.27 ng/ml plasma. Shortly after removal of the ovaries (6 to 8 hrs), baseline LH (2.2± .14 ng/ml) and FSH (12.20±2.90 ng/ml) plasma concentrations in the ovariectomized swine were significantly greater (P<.05) than those found in the intact and sham operated animals, but baseline prolactin concentrations (6.70±2.10 ng/ml) were not significantly different (P>.05) from the controls. The temporal patterns of maximum plasma concentrations associated with LH (3.47±.21 ng/ml), FSH (21.43±.82 ng/ml) and PRL (9.32±2.00 ng/ml) peaks were not similar among the ovariectomized animals. Baseline LH (1.12±.34 ng/ml), FSH (5.30±2.09 ng/ml) and PRL (6.05± 1.89 ng/ml) concentrations in the hysterectomized swine were not significantly different (P>.05) from the baseline concentrations in the intact and sham operated animals. Numerous plasma LH peaks (14.30±4.59) were observed during the 20-day collection period. These peaks averaged 19.50 ±1.49 hrs in duration and reached maximum concentrations of 2.63±.23 ng/ ml before returning to baseline. Plasma FSH and PRL peaks averaged 21.00 ±4.51 and 17,69±3.50 hrs in duration and reached maximum concentrations of 8.12±1.95 and 10.18±2.95 ng/ml before returning to baseline. Mean plasma LH concentrations in the intact, sham, ovariectomized and hysterectomized swine were significantly greater at the 2400 hr collections than at the 1800 hr collections. A critical assessment of plasma hormone concentrations is an essential prerequisite to a basic understanding of the physiological mechanisms governing the reproductive process. The descriptive data provided by this study will enable future investigators to design critical experiments to evaluate the physiological importance of these hormone fluctuations, thereby broadening our basic understanding of the mechanisms which govern the reproductive cycle.