Blockade of recruitment of ovarian follicles by suppression of the secondary surge of follicle-stimulating hormone with porcine follicular field.

Abstract

The increased serum concentration of follicle-stimulating hormone (FSH; follitropin) between proestrus and estrus in the rat has been hypothesized to recruit the follicles destined to During the afternoon of the day known as proestrus in the rat estrous cycle the two gonadotropic hormones, luteinizing hormone (LH; lutropin) and follicle-stimulating hormone (FSH; follitropin), surge between 1400 and 2000 hr (1,2). By midnight between proestrus and the next day, estrus, the serum LH level returns to baseline but FSH remains increased throughout the night until 1200 hr on estrus (1-3). This continued secretion of FSH has been called the "secondary FSH surge."Reflecting the marked alterations in serum gonadotropins, between the mornings of proestrus and estrus there is also a discontinuous growth of ovarian follicles into the "pre-Graafian " size class, 390-500 gm in diameter (4, 5). McClintock.and Schwartz (6) first proposed that, although the LH surge terminated the cycle in progress by inducing ovulation, the FSH secretion at proestrus initiated the recruitment of the cohort of follicles that would ovulate in the next cycle.Recently an experimental tool has become available for selectively suppressing serum FSH without altering serum LH or interfering with radioimmunoassay of blood levels of gonadotropin, as does antiserum to gonadotropic hormones (7,8).Porcine follicular fluid (PFF) contains a protein called "folliculostatin" or "ovarian inhibin" which inhibits the secretion of FSH specifically in both intact and ovariectomized female rats (9-13). In fact, Schwartz and Channing (11) have shown that injection of PFF late in proestrus (1545 and 1830 hr), after the primary LH and FSH surges have taken place, specifically suppresses the secondary FSH surge. Moreover, PFF administered earlier on the day of proestrus (1200 hr) suppresses the primary FSH surge without affecting the LH surge; however, after the effect of PFF wears off, the secondary FSH surge occurs (12,13). Thus, by using PFF it is possible to test the hypothesis that either the primary or the secondary FSH surge in proestrus and estrus is necessary for the recruitment of ovarian follicles.In the present study ovarian follicles in 50-,m diameter size classes from 250 to >500gum (preovulatory) were measured in four protocols. In experiment I, ovaries from untreated control rats were removed on the mornings of proestrus and estrus, to establish the timing of the phenomenon of follicular recruitment in our rats showing 4-day estrous cycles. In experiment II, rats were treated with PFF late in proestrus to block the secondary FSH surge (11) and were autopsied on the morning of estrus. In experiment III, rats were treated with PFF early in proestrus, to block the primary FSH surge (12), and were autopsied on the morning of estrus. Follicular recruitment was blocked when the secondary, but not the primary, FSH surge was suppressed. Moreover, in experiment IV, replacement with ovine FSH restored follicular recruitment in a dose-dependent manner.

Quantitative analysis of in-vitro incorporation of [3H]thymidine into hamster follicles during the oestrous cycle

“…(Bast & Greenwald, 1974). Beginning at 22:00 h on Day 4, there is an increase in serum FSH, accompanied by low levels of LH, which is sustained throughout the afternoon of Day 1 (Siegel, Bast & Greenwald, 1976 (Peluso & Steger, 1978) and causes follicular recruitment in the rat (Hoak & Schwartz, 1980) and in the hamster (Greenwald, 1975;Greenwald & Siegel, 1982). Eshkol & Pariente (1984) have shown that FSH significantly stimulates [3H]thymidine incorporation in rat granulosa cells in culture while hCG has no effect.…”

Functional specificity of the rainbow trout (Oncorhynchus mykiss) gonadotropin receptors as assayed in a mammalian cell line

“…The physiological significance of high FSH levels and FSHR gene expression during oocyte maturation and spawning in salmonids remains puzzling. However, in mammals (Hoak & Schwartz 1980) and fish (Prat et al 1996, Tyler et al 1997, it has been proposed that FSH plays a role in follicle recruitment for the next reproductive cycle. Meanwhile, recombinant FSH injected into female rats induces not only follicle growth but also ovulation (van Cappellen et al 1995).…”

Acute regulation of murine follicle-stimulating hormone β subunit transcription by activin A

“…Although there are fewer data in mice, the pattern of FSH release across their estrous cycles appears to be very similar (Nequin et al 1979, Tejada et al 1998, Ahn et al 2004. Whereas the primary FSH surge has limited or no functional relevance (DePaolo et al 1979, Hoffmann et al 1979, the secondary surge is fundamentally required for persistent cycles of ovarian follicle selection and maturation (DePaolo et al 1979, Hoak & Schwartz 1980. Given their relative physiological importance, it is noteworthy that the primary surge in rats depletes intra-pituitary FSH stores (Ortolano et al 1988, Chapman & Woodruff 2003.…”