Effect Of Ovulation Research Articles

Mechanisms of ovulation in female rats treated with FSH at the beginning of the estrous cycle: changes in pituitary responsiveness to luteinizing hormone releasing hormone (LHRH).

This study investigated the mechanisms of superovulation in 4-day cyclic female rats treated with two successive doses of 150 μg/100 g BW FSH in the afternoon of diestrus 1 and in the morning of diestrus 2. Following FSH treatment, a significant decline in LH release was observed during the critical period of the cycle on proestrus at 1700 h. FSH release appeared to be completely prevented at this moment of the cycle. After pentobarbital (PB) administration on proestrus at 1330 h, ovulation failed to occur in FSH-treated females injected with a dose of 200 ng LHRH i.v. This dose resulted in full ovulatory effects in control rats not treated with FSH. Infusion of 50 ng LHRH/h under PB blockade on proestrus, which caused a rise in blood LH within 30 min and resulted in full ovulation on the next morning in the controls, remained without effect in FSH-treated rats. LHRH infusion of 1000 ng/h was necessary to induce superovulation and the formation of an excessive number of corpora lutea with included oocyte in FSH-treated rats. A decrease in plasma estradiol-17β concentration was observed at 2400 h during the night from diestrus 2 to proestrus in FSH-treated rats. No changes in plasma progesterone concentration were observed during the time period extending from the morning of diestrus 2 to the afternoon of proestrus. Changes in the positive feedback action of estradiol on the hypothalamic pituitary system were supposedly then involved in the decrease in pituitary responsiveness to LHRH in FSH-treated rats.

Ovarian Responses of Pregnant Mare Serum Gonadotropin- and Human Chorionic Gondotropin-Primed Rats: Desensitizing, Luteolytic, and Ovulatory Effects of a Single Dose of Human Chorionic Gonadotropin*

We conducted a study to determine the morphological appearance and functional responsiveness of ovarian tissues after administration of hCG to 28-day-old rats primed 65 h earlier with PMS gonadotropin (PMSG) and after administration of a second dose of hCG 5 days later, i.e. to 33-day-old rats containing heavily luteinized ovaries. Sixty-five hours after the administration of 50 IU PMSG sc to 25-day-old rats, ovaries already contained an abundance of luteinized follicles and an adenylyl cyclase (AC) system that was responsive to LH, epinephrine, and NaF. The administration of 50 IU hCG sc at this time initially resulted in a loss of LH-responsive ovarian AC. Within 4 days of the hCG injection, the ovaries of the now 32-day-old rats were heavily luteinized, and ovarian AC was highly responsive to LH, epinephrine, and NaF. The administration of a single sc dose of 200 IU hCG to 33-day-old PMSC- and hCG-primed rats with luteinized ovaries resulted in a rapid desensitization of the ovarian AC to LH and a drop in serum progesterone levels, During the subsequent 7 days, serum progesterone levels continued to decline, while total ovarian AC reacquired responsiveness to LH by days 4--5 after the densensitizing dose of hCG. Dissection of ovarian components revealed, however, that the AC system of the corpora lutea originally present at the time of the second hCG injection remained permanently refractory to LH and that the AC in corpora lutea newly formed from freshly ovulated follicles exhibited a significant responsiveness to LH, epinephrine, and NaF. However, these new corpora lutea were not fully active, since serum progesterone never rose. Subcutaneous administration of 50 IU hCG to 33-day-old PMSG- and hCG-primed rats also promoted a rapid loss of AC responsiveness to LH. This lower concentration of hCG was not sufficient to promote follicular development or ovulation, and the ovarian AC remained refractory to LH for at least 7 days. Intravenous administration of 75 IU hCG to 33-day-old PMSG- and hCG-primed rats similarly promoted a rapid and permanent loss of luteal AC responsiveness to LH; again, follicles did not mature to a preovulatory state and, in fact, appeared to undergo atresia rather than ovulation. These results indicate that in heavily luteinized ovaries 1) hCG promotes desensitization of rat luteal AC to LH, 2) Desensitization of AC to LH stimulation in corpora lutea is permanent and irreversible, and 3) only under conditions where follicles mature and ovulate and new corpora lutea are formed does total ovarian AC reacqure responsiveness during the subsequent week.

Correlation between the effects of neuroleptics on prolactin release, mammary stimulation and the vaginal cycle in rats.

The correlation between hyperprolactinaemia induced by the administration of neuroleptic drugs, disturbances of the vaginal cycle and mammary gland stimulation in rats was investigated as a test model simulating the clinical syndrome of hyperprolactinaemia and amenorrhoea with anovulation. In acute experiments in which clozapine, sulpiride and chlorpromazine were administered orally to rats of both sexes, there were rapid increases in the level of prolactin in the serum with peak values between 15 and 60 min. The responses of female rats to various doses of sulpiride were consistently higher than those of male rats. Hyperprolactinaemia induced by sulpiride in dioestrous rats failed to desensitize the ovaries to the ovulatory effect of exogenous luteinizing hormone releasing hormone. Studies of these substances and of metoclopramide, haloperidol and thioridazine were then carried out in females rats by daily oral administration over a period of 13 days. The increases in the level of prolactin in the serum were paralleled by disruption of the vaginal cycle up to and including constant dioestrus and by mammary gland stimulation which, like the preceding phenomena, showed dose-dependence. The potencies of these six neuroleptics, as estimated from their effects on the mammary gland, appeared to be haloperidol greater than sulpiride greater than or equal to metoclopramide = thioridazine greater than chlorpromazine greater than clozapine.

Superovulation, Compensatory Ovulation, and Unilateral Inhibition of Ovulation by Selective Ovarian X-Irradiation of Immature Rats: Possible Modes of Action

The gonadotropin-primed immature rat was evaluated as a possible model system for studying X-irradiation effects on ovulation produced in mature rats. These effects include superovulation in whole-body irradiated animals and selective inhibition of ovulation when only one ovary is irradiated. This model, if suitable, would allow study of the hormonal factors involved in producing these ovulatory changes. BLU-LE females (26 days old) were given 4 IU of PMS and 15 IU of HCG to induce ovulation, and one or both ovaries were exposed to 400 R of X-irradiation. Other groups were unilaterally ovariectomized after X-ray. We were able to mimic in immature rats the array of X-ray-induced ovulatory effects observed in adult rats, and conclude that this system is a suitable model system for studying the mechanisms of action utilizing controlled amounts of exogenous gonadotropins.

Induction of ovulation in rabbits by synthetic luteinizing hormone-releasing hormone

The biological activity of synthetic luteinizing hormone-releasing hormone (LH-RH) was demonstrated by the induction of ovulation in estrogen-primed white rabbits. When the priming doses of estrogen were greater than 40 mcg and therefore too high an inhibitory effect was observed. The ovulatory effect of LH-RH was completely blocked by 6 mg progesterone.

Absence of bimodal ovulatory effect of PMS in the 30-day-old rat. 1.

SummaryThe effect of a single injection of varying amounts of PMS on ovulation in 30-day-old rats was investigated. Doses as small as 2 IU caused ovulation in some of the animals. Ova were ovulated in 100% of the animals injected with doses ranging from 3 to 67 IU. The incidence of ovulation declined with higher doses. A mean maximum of 68.7 ova was obtained with 55 IU and declined with larger amounts. A segmentation of ova was observed with 30 IU of PMS and higher.

A possible mechanism of the ovulation-inhibiting effect of chlormadinone acetate in the rat.

SUMMARY To study the mechanism of the ovulation-inhibiting effect of chlormadinone acetate, different quantities of this progestogen were implanted into one or both ovaries of dioestrous female rats. Introduction of the subcutaneously effective dose into one ovary suppressed ovulation in both, but implantation of half of this quantity did not influence spontaneous ovulation. On the other hand, 1/100 of the subcutaneously effective dose, implanted into the medio-basal hypothalamus or the anterior pituitary of adult dioestrous female rats, and of prepubertal females simultaneously injected with oestradiol benzoate, inhibited spontaneous and oestrogen-induced ovulations respectively. In juvenile rats the main site of action was the median eminence—anterior pituitary region. Chlormadinone was then implanted into the anterior hypothalamus or the anterior pituitary of adult dioestrous rats, and the median eminence was electrically stimulated during the 'critical period' in pro-oestrus. Since implants in the adenohypophysis prevented ovulation whereas implants in the anterior hypothalamus did not, a hypophysial site of action is suggested. On the basis of these results and of former findings on the action of oestrogens in ovulation, a hypothesis involving a competitive antagonism between oestrogen and progestogen at the hypophysial level is advanced to explain the acute ovulatory effects of these steroids.

Facilitation of pituitary-induced frog ovulation by progesterone in early fall.

SummaryIn October, when Rana pipiens ovaries are notoriously insensitive to ovulatory influences, injection of one frog pituitary gland in combination with small dosages of progesterone induced nearly complete ovulation within 24 hours. Progesterone, and to a lesser extent testosterone, also exerted some ovulatory effect when injected alone.

New Copper Compounds Inducing Ovulation by Sex-Center Activation

Ovulatory effects of copper gluconate were firstly reported. Ovulation was successfully induced by intravenous administration with this compound, which showed the least toxicity among the known copper compounds.