Effect of porcine follicular fluid preparations on gonadotrophin secretion by the mouse pituitary gland in vitro

Abstract

The acute effects of pooled porcine follicular fluid (PFF), before and after various methods of processing to eliminate steroids, were studied on the luteinizing hormone releasing hormone (LH-RH)-induced release of FSH and LH by whole pituitary glands, from 34-day-old mice, incubated in vitro for 3–4 h. Charcoal treatment of PFF eliminated the steroids and reduced the inhibitory potency on gonadotrophin secretion. On the other hand, dialysis or ultrafiltration (mol. wt > 10 000) did not reduce the inhibitory activity on gonadotrophin secretion. Of the three steroids tested, only oestradiol at a concentration of 10⁻¹⁰ mol/l inhibited FSH and LH secretion in vitro. This inhibitory effect was counteracted by the inclusion of the oestrogen antagonist tamoxifen in the incubation medium. The presence of tamoxifen did not decrease the suppression of FSH and LH induced by PFF, suggesting that the inhibition observed under the conditions of incubation was not due to oestrogen. Preincubation of mouse pituitary tissue for 1 h with PFF reduced the subsequent release of bioactive FSH and LH induced by LH-RH. The inhibitory effect of PFF was rapid and sustained. The continuous presence of PFF throughout the incubation period was not necessary for manifestations of the inhibitory effects on gonadotrophin release. The suppression of gonadotrophin secretion was related to the dose of PFF with the curve showing a biphasic pattern. The degree of FSH suppression was uniformly greater than that of LH, showing the preferential nature of the inhibitory effect of PFF. At high doses of PFF, the degree of FSH suppression was decreased significantly. This effect on LH release was less pronounced. The inhibition caused by PFF in the in-vitro incubation procedure was not due to destruction of LH-RH or the released gonadotrophins.