Ongoing studies in this laboratory are designed to determine the role of androgens in the maintenance of the erectile response in the rat. Testosterone-treated castrated rats (TESTO) and untreated castrated rats (CASTRATE) were used for measurement of the rate at which blood flows into the cavernous sinuses by timed collections of blood after partial amputation of the penis. A laser Doppler flow meter was employed to determine whether androgens also regulate the veno-occlusive mechanism that controls the rate of blood flow out of the sinuses. Erection was induced by direct electrical stimulation of the autonomic ganglion that controls cavernosal blood flow in the erectile response. The results of these studies showed that blood flow into the sinuses was approximately twice as great in the TESTO animals as the CASTRATE rats. Furthermore, during ganglionic stimulation, veno-occlusion occurred in the TESTO rats but failed to occur in the CASTRATE rats. The dependence of these responses on nitric oxide (NO) was demonstrated by showing that injection of sodium nitroprusside (SNP) enhances the intracavernosal pressure response in TESTO rats but not CASTRATE animals. However, when SNP injection was combined with ganglionic stimulation, veno-occlusion did occur in the CASTRATE animals. Taken together, these studies show that both the rate of blood flow into the cavernous sinuses and the blood flow out are under androgenic regulation and may involve the actions of NO.
Estrogens have been reported to exert both stimulatory and inhibitory effects on granulosa cell function. Previous studies from our laboratory showed that 12 h after administration of diethylstilbestrol (DES; a synthetic estrogen), FSH-stimulated granulosa cell proliferation and aromatase activity were increased; however, 48 h after DES, FSH stimulation of both parameters was inhibited. In other experiments, exposure of rats to DES for a period of 26 h blocked ovulation in response to eCG and hCG administration, whereas the same treatment regimen without DES caused ovulation in all treated rats. Thus, DES may in some cases actually interfere with maturation and development of ovulatory follicles. The present study was designed 1) to confirm that the duration of estrogen pre-exposure determines the way granulosa cells respond to FSH and 2) to investigate the underlying mechanisms involved. While DES was used in preliminary experiments, the majority of the studies were conducted with estradiol, a natural estrogen, in order to conform as closely as possible to the normal physiology. In the experimental protocol, immature female rats received injections of DES or implants of estradiol pellets 12 h (short exposure) or 36 h (long exposure) before 36 h of FSH treatment. Rats were killed, ovaries removed, and granulosa cells collected at the end of the FSH treatment period. The results demonstrate that exposure to either of these estrogens for 12 h allowed the subsequent FSH stimulation to produce high cellular proliferation, high aromatase enzyme activity, and large amounts of FSH receptor and aromatase mRNA. Estrogen exposure for 36 h, however, resulted in significantly decreased FSH stimulation of all these parameters. These findings confirm that short exposure to estrogen enhances the response of granulosa cells to FSH while longer exposure makes granulosa cells refractory to FSH. This differential sensitivity of granulosa cells to estrogen exposure could help explain how dominant follicles survive to ovulate while others are lost to atresia during ovarian cycles.
Porcine follicular fluid (pff), treated with charcoal to remove steroids, was used to determine whether inhibin is active in the laboratory rabbit. When pff (5 ml/4 kg body weight) was injected (ip) into does that had been castrated 2 weeks earlier, there was a significant decline in blood follicle-stimulating hormone (FSH) levels; the decline lasted for 8-12 h. Blood levels of luteinizing hormone (LH) were suppressed, but only briefly at 3 h after injection. In other experiments, intact does which had been injected with pff 9 h and 10 min before receiving a single, i.v. injection of luteinizing hormone-releasing hormone (LHRH) (10 micrograms/kg body weight) showed a sharp reduction in the concentration of LH in the blood samples collected 15, 30 and 60 min after LHRH administration. Secretion of FSH responded poorly to LHRH stimulation, and pff had little suppressive action on blood levels. Having established that the pff preparation had inhibin activity, its action on the postovulatory surge of FSH secretion was next examined. This release of FSH, which occurs 6 to 36 h after ovulation, has been hypothesized to be required for the establishment of pregnancy by stimulating the growth of the ovarian follicles supplying the luteotropic estradiol. To test this hypothesis, pff was injected into rabbits every 8 h for the first 5 days of pregnancy and found to block the postovulatory FSH surge. The patterns of secretion of LH and progesterone in the same pff-injected animals were, however, not altered from normal pregnancy patterns by pff.(ABSTRACT TRUNCATED AT 250 WORDS)
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