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Search for other papers by J. J. CURRY in
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SUMMARY
Intact control and sham-operated rats, when given sodium pentobarbitone at 13.30 h on the day of pro-oestrus, mated (controls, 10/12; shamoperated, 13/15) that night and underwent copulation-induced ovulation. However, after removal of the olfactory bulbs only 13 out of 23 pentobarbitone-blocked rats mated. Of the mated animals only six ovulated as compared with ten in the unoperated group and ten in the sham-operated group. The incidence of ovulation in all non-mated animals was low. In addition, the bulbectomized, mated animals which ovulated shed significantly fewer ova than did intact controls and sham-operated rats (6·8 as compared with 11·3 and 13·4, respectively). The incidence of mating in bulbectomized animals was also lower than in sham-operated animals when pentobarbitone was not given (8/16 and 8/11, respectively). Ovulation was essentially complete in all groups except in bulbectomized, mated rats which shed significantly fewer ova. It is suggested that olfactory inputs are important in mediating copulation-induced ovulation in the pentobarbitone-blocked rat and that copulation in the absence of olfactory inputs interferes in some way with the normal sequence of secretion of ovulatory hormone(s) in the non-blocked rat.
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Search for other papers by A. N. LOCKHART in
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SUMMARY
The release of ovulating hormone after acute treatment with gonadal steroids, or corpus luteum removal on different days of the oestrous cycle, was studied in the guinea-pig. Injection of 25, 50 or 100 μg oestradiol or 2·5 mg progesterone on day 13 of the cycle had no effect upon gonadotrophin secretion as judged by follicular histology, but markedly altered the sizes of the corpora lutea of the previous ovulation. Treatment with oestradiol on day 14 did not elicit gonadotrophin secretion. However, administration of the same hormones to animals given 10 μg oestradiol benzoate 24 h earlier caused ovulation or follicular luteinization. Progesterone (2·5 mg) appeared least effective in stimulating gonadotrophin release; 25 μg oestradiol were more effective when given at 12.00 h than at 24.00 h but treatment with both hormones caused ovulation when given at either time of day. Luteal volumes were not affected. Removal of corpora lutea during the second half of the cycle advanced the time of expected ovulation to day 15 or earlier when the procedure was carried out on days 8 or 9, but not on days 10–13. It is concluded that 4–5 days must elapse between the fall in plasma progesterone level associated with corpus luteum regression and the release of ovulating hormone.
Search for other papers by ROLAND BILLARD in
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Search for other papers by P. G. McDONALD in
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SUMMARY
In order to determine the sites at which oestradiol exerts its positive feed back effect, double-walled cannulae containing the antioestrogen ICI 46,474 were implanted into the preoptic area, median eminence or anterior pituitary. Implants were made at different stages of the cycle and left in place for between 4 and 96 h. Implants in the preoptic area for 24, 48 or 96 h did not significantly inhibit ovulation. Implants placed in the median eminence for 24 h before the critical period significantly inhibited ovulation when compared with controls (P < 0·02). Implantation of antioestrogen in the anterior pituitary for a similar 24-h period was ineffective in blocking ovulation. However, when mixed with cocoa butter and implanted in the anterior pituitary the antioestrogen significantly inhibited ovulation (P < 0·02). The results show that by preventing the action of oestradiol on either the pituitary or the median eminence, ovulation may be inhibited. Ovulation was not affected by implants in the preoptic region which suggests that this area is not involved in the positive feedback action of oestradiol.
Search for other papers by R. K. MEYER in
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Search for other papers by C. E. McCORMACK in
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SUMMARY
Ovulation in immature rats induced by daily subcutaneous administration of sheep follicle-stimulating hormone (FSH) was prevented by appropriately timed injection of phenobarbitone or by exposure to continuous light. Progesterone produced ovulation in light-blocked rats and in rats kept in standard lighting which had received a non-ovulatory dose of FSH.
These findings are interpreted to mean that ovulation produced by these preparations of FSH was due to a release of ovulating hormone from the pituitary gland. It is suggested that slight luteinizing hormone activity in an FSH preparation produces ovulation by causing the secretion of progesterone which then facilitates the release of ovulating hormone from the pituitary gland.
Search for other papers by H. M. A. Meijs-Roelofs in
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Search for other papers by G. A. Schuiling in
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ABSTRACT
Subcutaneous injections of an LHRH antagonist (ALHRH; Org.30093) were administered to immature female rats. Neither a single high dose (50 μg) nor repeated daily doses of 5–30 μg ALHRH/day, administered between 28 and 38 days of age, influenced the age and body weight at the time of vaginal opening or first ovulation. If repeated daily doses of 2 × 10 μg ALHRH were given from 32 to 42 or from 37 to 47 days of age, first ovulation was delayed by 3·0 and 6·3 days respectively. Administration of 10 μg ALHRH at 09.00 h and again at 17.00 h on the day of first pro-oestrus was found to be sufficient to block the expected first ovulation in 36 out of 38 rats. This effect could be repeated by administering the same doses of ALHRH at pro-oestrus and again on the next day: ovulation was blocked in eight out of eight rats. A single dose of 10 μg ALHRH, administered on the morning of pro-oestrus, blocked ovulation in five out of twelve rats. Both the preovulatory LH and FSH surge, as measured at 16.00 h on pro-oestrus, were found to be inhibited by ALHRH treatment.
On the day after pro-oestrus no recruitment of new small antral follicles had occurred in rats with ovulatory blockade. Delayed ovulation took place 2–5 days after ALHRH injection at pro-oestrus; until 3 days after injection rats were able to ovulate their original preovulatory follicles, thereafter newly developed follicles ovulated and large ovarian cysts were found in the ovaries, next to fresh corpora lutea.
Chronic administration of two injections daily of 10 μg ALHRH from 34 days of age until the morning of first pro-oestrus had marginal effects on the timing of first pro-oestrus and on follicle dynamics.
It was concluded that with the ALHRH compound used, and in chronic as well as in acute experiments, first ovulation could only be delayed by its administration on the day of first pro-oestrus and that the effect was due to acute inhibition of the preovulatory gonadotrophin surge.
J. Endocr. (1987) 112, 407–415
Search for other papers by R. P. CRAVEN in
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Search for other papers by P. G. McDONALD in
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SUMMARY
Cyclic female rats were treated with reserpine (5 mg/kg) on the 2nd day of dioestrus (15.00 h) or on the day of pro-oestrus (11.30 h) to produce a total or partial depletion of brain amines. Ovulation was inhibited in 18 out of 21 rats. Intrahypothalamic infusions of 0·4–80 μg dopamine or noradrenaline on the afternoon of pro-oestrus did not restore ovulation in reserpine-treated rats. In normal pro-oestrous rats, 80 μg dopamine significantly inhibited ovulation, whereas 80 μg noradrenaline had no significant effect. Electrochemical stimulation of the basal hypothalamus or the administration of luteinizing hormone induced ovulation only in those animals treated with reserpine at pro-oestrus. The results indicate that reserpine exerts a marked peripheral effect when given on the 2nd day of dioestrus and has a partial effect on the ovaries when administered at pro-oestrus. The failure of monoamines to induce ovulation suggests that some aminergic synapses involved in gonadotrophin release may lie outside the medial basal hypothalamus. In addition, high levels of dopamine appear to exert an inhibitory action on the release of pituitary gonadotrophins.
Search for other papers by L Hinojosa in
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The effects of thymulin administration beginning on days 19 or 24 of age on spontaneous puberty and gonadotrophin-induced ovulation were analysed in female normal and hypothymic mice. In normal and hypothymic mice, the daily administration of thymulin at 24 days of age resulted in a delay in the age of vaginal opening, with an increase in serum progesterone levels. Normal mice treated with 200 ng thymulin beginning on day 19 of age and injected with pregnant mare serum gonadotrophin (PMSG) 24 h later had an increase in ovulation rate, number of ova shed and weight of the ovaries. None of the hypothymic mice treated with thymulin on day 19 and PMSG on day 20 ovulated. PMSG treatment on day 25 induced ovulation in hypothymic mice. When these animals were injected previously with 200 ng thymulin, the number of ova shed by ovulating animals was lower than in PMSG-treated animals. Administration of thymulin and sequential injection of PMSG and human chorionic gonadotrophin 54 h later resulted in an increase in ovulatory response in comparison with those receiving only PMSG. The results suggest that thymulin plays a role in the regulation of spontaneous puberty through its effects on adrenal and ovarian endocrine functions. The increase in the ovarian PMSG response-treated animals, previously given thymulin, showed that this thymic hormone participates in the regulation of gonadotrophin secretion mechanisms and seems to be dose- and age-dependent. In hypothymic mice, neuroendocrine mechanisms regulating puberty are different from those of normal mice.
Search for other papers by P. G. McDONALD in
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Search for other papers by D. P. GILMORE in
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SUMMARY
Electrochemical stimulation of the basal and preoptic hypothalamus, under sodium pentobarbitone anaesthesia, was carried out on the day of pro-oestrus in normal cycling and in ovarian hormone-treated female rats. Control rats ovulated in response to 25, 50 and 100 μA for 60 s in the median eminence and to 10 μA for 60 s in the preoptic area. Oestradiol (1 μg) given 24 h before median eminence stimulation significantly increased the number of rats ovulating. An injection of progesterone (1 mg) 24 h before median eminence stimulation did not affect the number of animals ovulating or the number of ova shed. In contrast, there was a significant reduction in the number of animals ovulating after preoptic stimulation. Stimulation of the median eminence 2–4 h after progesterone administration increased the number of animals ovulating. The results suggest that both oestradiol and progesterone exert a positive feedback effect at or below the level of the median eminence and that the negative feedback effect of progesterone is exerted on the preoptic area.
Search for other papers by H. A. SHAPIRO in
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In a previous communication [Shapiro, 1936] it was shown that methyl testosterone, in common with certain other steroids, can induce ovulation in Xenopus laevis, the South African clawed frog. Zwarenstein [1936] showed previously that progesterone could also induce ovulation in Xenopus. His results have been reported more fully [1937].
Xenopus does not ovulate spontaneously under laboratory conditions of captivity. Even at the height of the breeding season, sexual activity disappears as soon as the animals are brought into the laboratory. The animal appears therefore specially suited for the investigation of gonadotrophic substances.
Shapiro and Shapiro [1934] described a seasonal cycle in the gonad ratio, i.e. the mass of the ovaries relative to the body-weight of the animal. This ratio reached a peak during the breeding season, which in South Africa extends approximately from July to September.
The following investigation was therefore undertaken with the object of constructing dose-response curves at
Search for other papers by PUSHPA SETH in
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Search for other papers by M. R. N. PRASAD in
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SUMMARY
Superovulation was induced in palm squirrels by the administration of gonadotrophins. The regimen of treatment effective in inducing ovulation was 60 i.u. pregnant mare serum gonadotrophin (PMS) administered in three doses of 20 i.u. on days 1, 4 and 7, followed by a single injection of 40 i.u. human chorionic gonadotrophin (HCG) on day 14. The same schedule of PMS and HCG administration induced ovulation in mature and immature squirrels both during the breeding season and the period of sexual quiescence. Ovulation did not occur in PMS-treated females if HCG was not administered. The period required for follicular growth before the follicles responded to the ovulatory stimulus of HCG was 13–14 days; the interval for follicular maturation leading to the release of the ovum was approximately 24 hr. Variations in the numbers of ova shed by different groups of females are related to the phase of the reproductive cycle and the age of the squirrels.
