Androgenic Modulation of Periovulatory Follicle-Stimulating Hormone Release in the Rat1

Abstract

We examined the relationship between the proestrous testosterone (T) surge and periovulatory follicle-stimulating hormone (FSH) release because previous evidence suggested that T may directly stimulate the selective release of FSH on estrus in the rat. In Experiment I, rats received flutamide (F) at either 1200 h on proestrus (F .times. 1) or 1800 h on Diestrus II and 1200 h on proestrus (F .times. 2). Additional animals received T-antiserum (T-A/S) at 1800 h on Diestrus II or vehicle (Control) at both times. In Experiment II, ovariectomized (OVX) rats (n = 11) were implanted with estradiol (E2)-filled capsules on Day 5 post-OVX; then, progesterone (P) capsules were implanted for 48 h beginning on Day 7 and again on Day 11. Six of these rats also received T capsules for 6 h on Days 7 and 11. All OVX rats were cannulated on Day 11 and bled every 4 h until they were killed on Day 12. In the first experiment, neither acute androgen receptor blockade with F .times. 1 nor T-A/S treatment altered the pattern of periovulatory FSH release, suggesting that the proestrous T surge does not directly stimulate estrous FSH release. However, longer blockade with F .times. 2 suppresesd both the proestrous and estrous phases of FSH release, implying that an androgenic stimulus moderates periovulatory release. In Experiment II, E2 and P capsules stimulated gonadotropin surges but not a selective, estrous-like elevations of T do not specifically result in selective FSH release. In conclusion, these data indicate that the proestrous T surge does not have a direct role in stimulating selective FSH relase on estrus, but androgenic modulation does appear to affect the ability of the pituitary gland to release FSH during the periovulatory period.