Circulating gonadotrophin surge-attenuating factor from superovulated women suppresses in vitro gonadotrophin-releasing hormone self-priming

Abstract

A perifusion system based on ovine pituitary tissue explants was used to investigate the effects of follicular fluid (hFF) and serum from superovulated women on pituitary responsiveness to gonadotrophin-releasing hormone (GnRH). The specific aims of the study were to determine both if gonadotrophin surge-attenuating factor (GnSAF) bioactivity is present in the peripheral circulation as well as in the follicles of superovulated women and if GnSAF suppresses GnRH self-priming in vitro. Two pulses of GnRH, 1 h apart, produced marked peaks in LH secreted from control chambers, with GnRH self-priming evident in the significant difference between the first (134.4 +/- 1.7 - 232.1 +/- 24.0% of basal secretion) and second (183.9 +/- 15.8 - 313.9 +/- 14.0% of basal secretion) LH peaks. Both follicular fluid and serum pooled from two different groups of women produced marked suppression of the first (unprimed) and second (primed) LH peaks. The hFF reduced the first LH peak to 69.6 +/- 7.8 and 60.2 +/- 9.7% and the second LH peak to 57.4 +/- 6.7 and 42.6 +/- 6.5% of control LH secretion. Overall, the serum reduced the first and second LH peaks to 76.8 +/- 4.2 and 62.9 +/- 3.6% of control respectively. These results demonstrated that GnSAF bioactivity suppresses GnRH self-priming, and is present in both the peripheral circulation and hFF. The same material administered to dispersed ovine pituitary monolayers produced similar marked suppression of GnRH-induced LH secretion, with approximately 50-fold less GnSAF bioactivity in serum compared with hFF. Combined doses of oestradiol and progesterone, or hFF from large follicles containing little GnSAF, produced stimulation of GnRH-induced LH secretion and GnRH self-priming (second peaks 78.1 +/- 38.9 and 27.4 +/- 15.7% respectively higher than first peaks). Thus, in conclusion, GnSAF in hFF and serum markedly attenuated both unprimed and primed pituitary response to GnRH, virtually abolishing the GnRH self-priming effect.

Gonadotropin Surge-Attenuating Factor Bioactivity in Serum from Superovulated Women is not Blocked by Inhibin Antibody1

“…A final possibility is simply that of nonspecific protein-loading effects. Using our ovine pituitary models [22], we have shown that the same batch of superovulated serum as that used in the present study markedly suppresses ovine pituitary responsiveness to GnRH. This was seen both in the pituitary monolayer system, which includes 12.5% of sera in the buffer, and in the pituitary perifusion model, where heat-inactivated plus charcoaltreated serum from non-superovulated humans was used to control for nonspecific effects.…”

Influence of ovarian manipulation on reproductive endocrinology in polycystic ovarian syndrome and regularly cycling women

“…GnSIF/AFs cannot be measured directly, because its molecular structure has not been fully identified yet. GnSIF/AF normally influences LH through inhibition of the GnRH-induced LH secretion and antagonizing the self-priming effect of GnRH (35,36,37). All measurable ovarian hormones in this study did not change, thus it is not likely that GnSIF/AF would be the only ovarian hormone that would change after the manipulation.…”

Follicle-Stimulating Hormone Stimulates Circulating Gonadotropin Surge-Attenuating/Inhibiting Factor Bioactivity in Cows1

“…This was necessary since the bioassay of 441 samples (147 individual blood samples, each at three different doses) would have been prohibitively expensive and time consuming. This approach has been used previously with samples from women and forms the basis of much of the current literature on GnSAF/IF bioactivity in biological fluids [12,31]. Performed carefully, these pools of equal volumes of plasma from equal numbers of animals yield data that correlate closely with data from all the samples assayed separately.…”

“…This effect has been attributed to the putative ovarian hormone gonadotropin surge-attenuating/inhibiting factor (GnSAF/IF) [9] and is supported by data indicating that GnSAF/IF reduces GnRH self-priming, an important component of the LH surge, both in vivo [10] and in vitro [11,12]. Treatment with FSH stimulates the production of GnSAF/IF bioactivity in vivo in humans, monkeys, and rats [13][14][15][16][17][18][19][20].…”