Effects of Single Injections of Bovine Follicular Fluid on Gonadotrophin Concentrations Throughout the Oestrous Cycle of the Rat

Abstract

A single injection of steroid-free bovine follicular fluid (bFF), which contains inhibin-like activity, was given to adult female rats at 09.00 h on dioestrus-2 (the day after metoestrus), dioestrus-3, pro-oestrus or oestrus. peripheral concentrations of gonadotrophins were measured at 2-h intervals after injection. Compared with values in control animals treated with bovine plasma, injection of bFF did not influence concentrations of LH. In contrast, at all days studied injection of bFF resulted in suppressed concentrations of FSH, during a period which started between 4 and 10 h after injection and lasted 4-12 h, depending on the day of the cycle. With the exception of pro-oestrus, the period of suppression was followed by one in which fluctuating levels of FSH were found; in general, resulting levels were higher though not significantly increased. This latter effect was most pronounced on dioestrus-2 and dioestrus-3, when levels of FSH, which were already low in control animals, were first suppressed during the 6 h after injection of bFF. These data, in conjunction with results from an earlier study in rats at dioestrus-1, showed that administration of bFF induces a fast and selective suppression of FSH secretion on all days of the cycle. This period of suppression was followed by one with fluctuating levels of FSH which showed a tendency to be higher, indicating that disturbances in FSH secretion, such as are caused by bFF, can be compensated for quickly. In this way the process of follicular maturation might be protected.

Inhibin increases in the ovaries of female rats approaching first ovulation: relationships with follicle growth and serum FSH concentrations

“…It is remarkable that around the same time (after day -6) serum FSH reaches levels equal to or below 200 pg/1 with much less ( <005) fluctuation than during the preceding period. Thus, a situation comparable to that during the adult cycle, with relatively low FSH con¬ centrations ( 200 pg/1) varying within narrow limits (Hermans, Debets, van Leeuwen & de Jong, 1982a), then develops for the first time at this stage in pubertal rats. This strongly suggests that ovarian ILA plays a role in the fine regulation of serum FSH during these last 5 days preceding first ovulation.…”

Potential application of inhibin in male and female contraception

“…There are reports indicating that the administration of follicular fluid during the normal ovarian cycle in rats suppresses the proestrus as well as the estrus FSH surge [12] and also affects follicular growth and ovulation [13]. In contrast to these findings, DePaolo and colleagues [14] and Nandedkar and colleagues [15] observed that inhibin did not affect ovulation in cyclic rats, nor did it alter oocyte maturation or ovarian morphology.…”

Inhibin-like activity in media from cultured rat granulosa cells collected throughout the oestrous cycle

“…Moreover, in the adult cyclic rat a relationship exists between the phase of the oestrous cycle and peripheral levels of FSH (see Nequin, Alvarez & Schwartz, 1979, for references), between the phase of the oestrous cycle and steroid and inhibin levels in ovarian venous plasma (OVP) (DePaolo, Shander, Wise et al 1979) and in follicular fluid (Fujii, Hoover & Channing, 1983) and, more directly, between fluctuations in the levels of FSH and inhibin (DePaolo, Anderson & Hirshfield, 1981;Hermans, Debets, van Leeuwen & de Jong, 1981, 1982a. It is therefore tempting to postulate that there is a closed feedback system between FSH and inhibin which plays a role in the regulation of the oestrous cycle and follicular growth.…”