Effect of FSH on ovarian inhibin secretion in anoestrous ewes

In Exp. 1, 7 Finn-Merino ewes which had one ovary autotransplanted to a site in the neck had jugular and timed ovarian venous blood samples collected at 10-min intervals for 2 h before and 3 h after injection of 5 micrograms NIAMDD-oFSH-S16. In Exp. 2, 8 Finn-Merino ewes with ovarian autotransplants had jugular and timed ovarian venous blood samples collected at 15-min intervals for 2 h before and 12 h after bolus injection of 40 micrograms NIAMDD-oFSH-S16 and infusion of oFSH-S16 at 6 micrograms/min for 4 h. In Exp. 2 the follicular population of the ovary was assessed by real-time ultrasound at the beginning and end of the experimental period. In both experiments the secretion rates of inhibin (1-3 ng/min) and oestradiol (0.5-8 ng/min) were similar to those observed during the luteal phase of the cycle in the breeding season, indicating significant follicular development in these animals. In Exp. 1 there was no change in the secretion of oestradiol or inhibin after the injection of FSH which resulted in a 25% increase (P less than 0.05) in the concentration of FSH in plasma. Inhibin secretion was pulsatile but there was no difference in inhibin pulse frequency before (1.6 +/- 0.2 pulses/h) or after (1.2 +/- 0.5 pulses/h) injection of FSH. In Exp. 2 injection of FSH resulted in an increase (P less than 0.001) in plasma concentrations of FSH in the sample taken 10 min after injection from a baseline of 1.2 +/- 0.2 ng/ml to a peak of 10.6 +/- 1.0 ng/ml (mean +/- s.e.m.).(ABSTRACT TRUNCATED AT 250 WORDS)