EFFECT OF PREGNANCY AND HYSTERECTOMY ON PITUITARY GONADOTROPINS SECRETION IN THE EWE

Two experiments were conducted to examine the effect of hysterectomy on Days 32-33 post mating on luteal and pituitary function in the ewe. In Experiment 1, progesterone concentrations in plasma collected every 2 days remained constant (> 1.5 ng ml -1) between Days 30 and 120 post mating and then gradually decreased over the next days reaching undetectable levels (< 0.1 ng ml-1) at luteolysis. Ewes resumed ovulation immediately after the regression of corpus luteum (CL) and formed a functional CL which was maintained for the duration of the sampling period (over 30 days). FSH concentrations remained fairly stable in plasma collected every 20 min for 7 h before (Day 30 post mating) and after (Days 60, 80, 100 and 120 post mating) hysterectomy. Mean (+/- s.e.m.) FSH concentration before hysterectomy (2.9 +/- 0.3 ng ml-1) was not significantly different (P> 0.05) from that on any day after hysterectomy (3.2 +/- 0.3, 3.5 +/- 0.8, 3.3 +/- 0.4 and 3.4 +/- 0.4 ng ml-1). In Experiment 2, FSH concentrations in plasma collected three times per week, between Days 20 and 120 post mating in sham operated and hysterectomized ewes showed no changes during the sampling period. There were no significant differences in FSH values between the two groups of ewes. Occasional LH pulses were detected in plasma collected every 1 5 min for 6 h on Days 20, 40, 60, 80, 1 00 and 120 post mating in sham operated and hysterectomized ewes. Mean (+/- s.e.m.) luteinizing hormone (LH) concentration on Days 20, 40, 60, 80, 100 and 120 post mating were respectively 0.53 +/- 0.08, 0.33 +/- 0.02, 0.28 +/- 0.01, 0.45 +/- 0.09, 0.42 +/- 0.02 and 0.38 +/- 0.05 ng ml-1 in sham operated ewes, 0.62 +/- 0.10, 0.37 +/- 0.03, 0.50 +/- 0.05, 0.38 +/- 0.09, 0.39 +/- 0.08 and 0.39 +/- 0.08 ng ml-1 in hysterectomized ewes. There were no significant differences (P> 0.05) between the two groups of ewes in the mean LH concentrations in any of the six post-mating stages examined. In conclusion, hysterectomy during early pregnancy prolongs CL lifespan for a period equivalent to that of pregnancy, but has no effect on pituitary FSH and LH secretion. The significance of these findings, particularly with regard to follicular development during late pregnancy is discussed.