Ovine follicular fluid suppresses the ovarian secretion of androgens, oestradiol and inhibin.

An experiment was conducted to examine the effect of steroid-free ovine follicular fluid (oFF) on ovarian hormone secretion. Eight Merino x Finnish Landrace ewes in which the left ovary and vascular pedicle had been autotransplanted to a site in the neck were studied during the breeding season. Luteal regression was induced in all animals by injection of cloprostenol (100 micrograms, i.m.) on day 10 of the luteal phase. Four of the eight animals were treated with steroid-free oFF (3 ml, s.c.) in the early follicular phase, 24 and 36 h after injection of cloprostenol. Samples of both ovarian and jugular venous blood were collected at 4-h intervals from 20 h before until 96 h after injection of cloprostenol. Ovarian and jugular venous blood samples were also collected at 10-min intervals from 48 to 52 h after injection of cloprostenol to investigate the pattern of pulsatile secretion of ovarian hormones. Samples were assayed for oestradiol, androstenedione, testosterone and inhibin and the ovarian secretion rates calculated. Both injections of oFF resulted in a fourfold increase in the concentration of inhibin in jugular venous plasma within 4-8 h of administration (P less than 0.01) with concentrations remaining increased (P less than 0.05) until 56 h after cloprostenol (32 h after the first oFF injection). Following oFF injection there was a profound (100%; P less than 0.001) and prolonged decrease in the peripheral concentration of FSH until 60 h after cloprostenol at which time the concentration of FSH increased five- to sixfold (P less than 0.001) to a peak lasting 24 h. In contrast to FSH, the concentration of LH in jugular venous plasma rose immediately following oFF treatment and continued to increase, exhibiting a profile similar to that described for FSH. No preovulatory LH surge was detected in any of the oFF-treated ewes while untreated ewes had an LH surge within 58.0 +/- 1.2 (S.E.M.) h. Within 8 h of the first injection of oFF the ovarian secretion rate of oestradiol, androstenedione and inhibin began to decline to reach a nadir of less than 1 ng/min within 32-36 h (56-60 h after cloprostenol; P less than 0.01). Testosterone secretion, already barely detectable, did not change significantly following injection of oFF but remained low for 36 h following oFF and did not exhibit the increase observed over this period in controls. After injection of oFF the episodic secretion of oestradiol, androstenedione, testosterone and inhibin was markedly suppressed in spite of numerous pulses of LH.(ABSTRACT TRUNCATED AT 400 WORDS)