Steroid feedback regulation of luteinizing hormone and follicle-stimulating hormone secretion rates in male and female rats

Effect of supplemental heat on mortality rate, growth performance, and blood biochemical profiles of Ghungroo piglets in Indian sub-tropical climate

AIM

The present study was conducted to explore the effect of supplemental heat on mortality rate, growth performance, and blood biochemical profiles of indigenous Ghungroo piglets in sub-tropical cold and humid climatic conditions of Tripura, a state of the north eastern hill (NEH) region of India.

MATERIALS AND METHODS

The experiment was conducted on 38 indigenous Ghungroo piglets from birth up to 60 days of age. Among the 38 piglets, 19 piglets were provided with supplemental heat ranging between 17.0°C and 21.1°C for the period of the first 30 days and thereafter between 24.1°C and 29.9°C for the next 30 days. The other 19 piglets were exposed to natural environmental minimum temperatures ranging between 7.2°C and 15.0°C during the first 30 days and then between 18.5°C and 25.5°C for the next 30 days.

RESULTS

The supplemental heat resulted in 10.6% reduction of piglet mortality from the 2(nd) till the 7(th) day of age. These beneficial effects could be related with the lower (p<0.05) plasma glutamate pyruvate transaminase (GPT) and cortisol levels and higher (p<0.05) plasma alkaline phosphatase (AP) concentrations in heat supplemented group compared to control group. Plasma AP, GPT, glucose, triiodothyronine, and luteinizing hormone concentrations decreased (p<0.05) gradually with the advancement of age in both control and supplemental heat treated piglets.

CONCLUSION

Supplemental heat could be beneficial since it is related to a reduction of piglet mortality during the first week of life under farm management system in the sub-tropical climate of NEH region of India.

Inhibition of lordosis behavior in male and female rats by androgens and progesterone

Several studies suggest that when manipulated experimentally in adulthood, the lordosis response to estrogen can be increased dramatically in male rats. Because adult-gonadectomized (Gx) animals were used in these studies, the lack of testicular hormones in adulthood may have been a factor. To examine this possibility, adult-Gx rats were implanted with blank (Bk)-, testosterone (T)-, 5alpha-dihydrotestosterone (DHT)-, or progesterone (P)-filled capsules, alone or in combination. We report a new finding, that a combined treatment of T plus P (T+P) at physiological doses for the male, but not T or P alone, reduced lordosis significantly in males, with and without estrogen priming. T+P did not inhibit lordosis in females, nor did this specific treatment affect open field, aggressive, and male copulatory behaviors. In confirming studies done with much higher doses, DHT reduced lordosis in both sexes. DHT and T+P also reduced lordosis in adrenalectomized/Gx males. Mechanisms responsible for the T+P inhibition of lordosis in males are not known, but they may include an upregulation of androgen receptors by P, and this possibility is discussed.

Effects of ovariectomy and ovarian steroids on binding of 3H-mepyramine, an H1-histamine antagonist, in rat hypothalamus

The effects of ovariectomy and ovarian steroids on 3H-mepyramine binding, a histamine antagonist considered as a suitable ligand for H1-histamine receptors, were studied. Saturation binding assays and Scatchard plot analyses were performed in membranes from hypothalamus of adult female rats. In the hypothalamus of ovariectomized (OVX) rats, a decrease of the Bmax and a lowering of Kd values as compared to diestrous rats, were found. Estradiol administration to OVX rats as a single SC injection (25 micrograms), or by means of SC Silastic capsules (500 micrograms/ml estradiol benzoate; 10 mm/100 g b.wt.), reversed the effects of OVX, increasing both Bmax and Kd. The addition of progesterone (25 mg) blunted the effects of estradiol (50 micrograms). The present results suggest that hypothalamic H1-histamine receptors may be modulated by the ovarian steroids and provide further evidence of a possible role of histamine in female gonadotropin regulation.

Detection of folliculostatin: a sensitive and specific bioassay using the female rat

To establish a sensitive and specific bioassay for the FSH-suppressing activity present in porcine follicular fluid (pFF), we examined the latency of pFF action when injected IV in the acutely ovariectomized (ovax) metestrous rat. By 2h post injection (5.5h after ovax), FSH was suppressed significantly in pFF vs. porcine serum-injected controls. LH was unaltered. In an experiment establishing a dose-response curve for pFF 4.5h after injection, 1.77 mg of pFF protein significantly suppressed FSH. The index of precision (-0.2188) and precision of slope (1.088) were well within acceptable limits for bioassays. We conclude that the ovax metestrous rat, injected 3.5h after surgery and sacrificed at 4.5 or 5.5h, is a sensitive and specific bioassay for folliculostatin.

Specific FSH suppression in male rat by porcine follicular fluid

A variety of protocols using intact, castrated, and sham-castrated adult male rats was used to test the ability of porcine follicular fluid to selectively suppress serum follicle-stimulating hormone (FSH). A total dose of 500 microliters follicular fluid injected intraperitoneally will suppress FSH in the rat with testes within 5 h of injection. This is more than is necessary to suppress FSH in the intact or ovariectomized female. A total dose of 1 ml of follicular fluid is needed to suppress FSH reliably in the castrated male rat. Serum FSH is suppressed significantly beginning between 4 and 5.5 h after intraperitoneal injection of 1 ml of follicular fluid and 3 h after intravenous injection. The suppression continues until 10 h postinjection and is abated by 26 h postinjection. Serum luteinizing hormone (LH) is unaffected by follicular fluid in any protocol tested. It is concluded that 1) follicular fluid can suppress serum FSH in the male if large enough doses are given, 2) follicular fluid has no effect on serum LH, and 3) follicular fluid suppresses serum FSH levels in the male as well as previously tried testicular sources. These results suggest that the delay in demonstrating the existence of inhibin may be due to the use of males as both source and test subject.

Effect of testosterone on the hypothalamic-pituitary-gonadal axis of pinealectomized and pineal-intact male rats

Previous studies indicate that steroid hormones alter pineal biochemistry, and it has been suggested that at least part of the negative feedback effect of steroid hormones on pituitary gonadotropin release may be mediated by the pineal gland. In this study, pinealectomy did not alter the inhibitory effect of testosterone on neuroendocine-gonadal activity in the male rat, suggesting that the pineal gland does not mediate the response of the rat hypothalamic-pituitary axis to testosterone.

Evidence for ovarian "inhibin": suppression of the secondary rise in serum follicle stimulating hormone levels in proestrous rats by injection of porcine follicular fluid

The present studies were carried out to see if porcine follicular fluid could inhibit increases in serum follicle stimulating hormone (FSH) levels when injected into the rat. For these studies the pentobarbital-treated proestrous rat was chosen as the major test animal model. If an artificial surge of luteinizing hormone (LH) is administered to these rats, it can induce a synchronized secondary rise in FSH secretion rate. Normal saline-treated rats were also used as test animals. They exhibit preovulatory endogenous "surges" of LH and FSH, and also a secondary FSH rise. Porcine follicular fluid was harvested from medium-sized and large (3- to 10-mm diameter) follicles and treated with charcoal to remove endogenous steroids. Charcoal-treated porcine serum served as a control solution. The fluid was injected intraperitoneally in two 0.5-ml doses into pentobarbital-treated proestrous rats immediately and 3 hr after LH injection. Follicular fluid, but not the serum, suppressed the secondary, LH-induced FSH rise (P < 0.01) in a dose-dependent manner, without altering the effects of LH upon serum ovarian steroid levels or follicular rupture. It was effective down to a total dose of 200 mul. Porcine follicular fluid also blocked the secondary FSH surge in normal proestrous rats exhibiting endogenous LH/FSH primary surges. Thus, it would appear that porcine follicular fluid contains a non-steroidal substance(s) that can block the secretion of FSH that is secondary to a natural or artificial LH surge.