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Search for other papers by S Furudate in
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Abstract
Endothelins vary in their biological activity. We therefore examined the effects of endothelin-3 (ET-3) on ovulation and secretion of LH, FSH and prolactin in rats in which naturally occurring ovulation was blocked by the administration of sodium pentobarbital (40 mg/kg, i.p.) prior to the critical period (1330 h) on the day of pro-oestrus. ET-3 (10 nmol/kg) was given via the jugular vein under pentobarbital anaesthesia from 1600 to 1800 h on the day of pro-oestrous and induced ovulation in all rats whether given by venous injection or by infusion but the number of ova in rats injected with ET-3 was less than that in normally cycling control rats. Infusion of ET-3 stimulated the secretion of LH but caused a lower than expected rate of secretion of FSH. It would therefore appear that ET-3 causes release of the total amount of LH that is required for induction of ovulation. Our findings strongly suggest that ET-3 has a physiologically significant role in the regulation of anterior pituitary hormone secretion.
Journal of Endocrinology (1994) 141, 109–112
Search for other papers by E. T. BELL in
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SUMMARY
The effect of the administration of 25 i.u. human chorionic gonadotrophin (HCG) on the induction of ovulation in intact immature rats treated with 50 i.u. pregnant mare serum gonadotrophin (PMSG) has been studied.
After the administration of HCG a marked increase in ovarian wet weight was observed. The maximum increase, which occurred 10 hr. after hormone treatment, was noted 2 hr. before ova were found in the oviducts.
The alteration in ovarian wet weight was associated with a fall in percentage solids. However, it appears likely that an increase both in follicular fluid and in cell mass occurred before ovulation. Possible reasons for the absence of any marked effect on uterine wet weight or percentage solids are discussed.
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Departments of Anatomy and Obstetrics and Gynecology, Louisiana State University Medical Center, New Orleans, Louisiana 70112, U.S.A.
(Received 31 January 1975)
The results of investigations on the effect of unilateral ovariectomy (ULO) in the hypothyroid rat are conflicting because increase in weight of the remaining ovary has been used as the endpoint (Schreiber, Zbuzkova-Kmentova & Zbuzek, 1968; Saiduddin, 1972). A more reliable indication of ovarian function is to determine the number of eggs shed. After ULO, twice as many ova as normal are ovulated from the remaining ovary (Peppier & Greenwald, 1970). In this report the effect of thyroidectomy for either 2 or 7 weeks on the pituitary-ovarian relationship in the rat was studied using the phenomenon of compensatory ovulation after ULO.
Virgin, female, Charles River rats were used in two separate experiments. Thyroid glands were surgically removed at 59 days of age under ether anaesthesia. In the first experiment
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Department of Gynecology and Obstetrics, The Human Development Centre, University of Kansas Medical Center, Kansas City, Kansas 66103, U.S.A.
(Received 18 February 1976)
Direct progesterone effects on the ovarian follicle have usually been ruled out because of the absence of a progesterone effect on the ovarian response to gonadotrophins in hypophysectomized animals (France & Pincus, 1964; Smith & Bradbury, 1966). In contrast, experiments on intact animals have provided evidence that either increased preovulatory production of progesterone in vivo, or its administration, can exert a positive modulating effect upon ovulation in-vivo (Meyer, Karavolas, Klausing & Norgard, 1971; Norman & Greenwald, 1971; Kobayashi, Hara & Miyake, 1973). Sridharan, Meyer & Karavolas (1974) found this positive action of progesterone to be time-dependent. They concluded that time of day, dosage of progesterone in relation to the stage of the oestrous cycle, and presence of other steroids, affect ovulation in in-vivo experiments. Recently, Takahashi, Ford,
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The routine procedure in this laboratory for the extraction of gonadotrophins from urine is a kaolin-acetone method (Brown, 1959). Recently, we have started using a new bioassay depending on induced ovulation in mice (Cunningham, 1962). The present investigation was undertaken to discover whether any other extraction methods would give consistently higher yields than Brown's method when gonadotrophin was measured by the ovulation assay. The methods selected are shown in Table 1. They were chosen as being comparable in speed and convenience with the method in present use; more laborious techniques such as those employing ethanol precipitation were excluded since they are unsuitable for routine use.
Techniques of extraction and grades of reagents were all similar to those specified in the published descriptions. Where the specified quantities were given in relation to a 24 hr. specimen, this was taken as equivalent to 1200–1500 ml. urine. The dried extracts were stored at
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Department of Obstetrics and Gynecology, Kyoto University School of Medicine, Sakyo-ku, Kyoto and * Division of Pharmacology, Teikoku Hormone Research Institute, Kawasaki, Japan
(Received 1 October 1976)
It is well known that ovulation is brought about by a surge of luteinizing hormone (LH). Ovarian steroidogenesis induced by LH has been implicated in the ovulatory process by the observation that ovulation is prevented by various inhibitors of steroidogenesis in immature rats primed with pregnant mare serum gonadotrophin (PMSG) (Lipner & Greep, 1971). Subsequently doubt was cast on this concept (Bullock & Kappauf, 1973), but recently it has been reported that a progesterone-dependent step exists in the normal ovulatory process in cyclic rats (Takahashi, Ford, Yoshinaga & Greep, 1974). However, the involvement of oestrogen in follicular rupture was not excluded in any of these experiments. In an attempt to obtain direct evidence of whether either steroid and, if so which, is essential for
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SUMMARY
Serotonin (5HT, 100 mg/kg) given subcutaneously between 16.00 and 18.00 h on the day of pro-oestrus, at 17.00 h on day 2 of dioestrus and at 13.00 and 17.00 h on day 1 of dioestrus, inhibited ovulation in adult rats. It was ineffective at 13.00 h on the day of pro-oestrus and on day 2 of dioestrus. The anti-ovulatory effect at 17.00 h during pro-oestrus was reversed by pretreatment with 2–4 mg progesterone or 2·5 mg dipyridamole/kg. The effect at 17.00 h on day 2 of dioestrus was reversed by 2 μg oestradiol benzoate. Subcutaneous injection of 5HT antagonized the ovulatory action of exogenous luteinizing hormone and inhibited the passage of 22Na into ovary, uterus and muscle but not the pituitary. Intraventricular administration of 5HT (200 μg/rat) between 13.00 and 18.00 h during pro-oestrus had no effect on ovulation. These results suggest that subcutaneous administration of 5HT does not inhibit ovulation at a central site, but acts as a peripheral vasoconstrictor preventing the passage of hormones to their target organs.
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SUMMARY
To study the positive feed-back mechanism by which oestrogen induces corpus luteum formation, electrolytic lesions were placed in different parts of the anterior hypothalamus of prepubertal female rats which were then injected with oestradiol benzoate. Ovarian luteinization did not occur when the main parts of the suprachiasmatic nuclei or of the medial preoptic area had been destroyed.
Oestradiol benzoate was implanted stereotaxically into the brain and the anterior pituitary of immature female rats. Whereas 1/25 of the subcutaneously effective dose had to be implanted into the anterior hypothalamus, 1/100 of the peripherally effective dose introduced into the adenohypophysis was sufficient to induce corpus luteum formation in most of the treated animals.
The results suggest that, although the anterior hypothalamus is necessary for this positive feed-back mechanism, the anterior pituitary may be the main site of action of oestrogen.
Oestrogen may increase the hypophysial sensitivity to the hypothalamic gonadotrophin-releasing factor. Thus an enhanced gonadotrophin secretion may result, sufficient for the induction of ovulation. The possibility is discussed that this positive feed-back mechanism is also essential for the induction of ovulation in women.
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ABSTRACT
Pentobarbitone-blocked pro-oestrous rats were subjected to either limited mating (maximum of 30 mounts), all-night cohabitation with males or stimulation of the vagina and cervix with a glass rod (2 or 5 min) to determine which type of stimulus was most effective in inducing ovulation. All-night cohabitation was the most successful procedure and resulted in 100% ovulation in those rats which mated. Treatment with either phenoxybenzamine, propranolol or pimozide did not interfere with this copulation-induced ovulation whereas methysergide treatment completely blocked copulation-induced ovulation. Administration of atropine resulted in a loss of mating behaviour and these animals therefore did not ovulate. Further experiments provided evidence that administration of atropine also blocked ovulation in response to vaginal stimulation with a glass rod. Pretreatment with methysergide or atropine had no effect upon the percentage of pentobarbitone-blocked, pro-oestrous rats ovulating in response to administration of LH releasing hormone (LHRH). However, those rats given atropine shed significantly fewer ova per rat following LHRH or LH infusion when compared with controls. These results suggest that the synaptic mechanisms responsible for mediating copulation-induced ovulation are different from those mediating steroid-induced ovulation, and that ovarian cholinergic receptors may play a role in ovulation.
J. Endocr. (1984) 100, 361–365
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High levels of plasma calcitonin (CT) have been detected in birds and other lower vertebrates (Kenny, 1971; Kenny, Boelkins, Dacke, Fleming & Hanson, 1972), but its role in these species remains unexplained (Kenny, 1972). In Japanese quail, plasma CT levels are higher in mature males than in egg-laying females (Boelkins & Kenny, 1970). It is possible that the level of plasma CT in females may vary during the ovulation cycle. We are investigating these levels with a view to elucidating the role of CT in the egg-shell calcification cycle of the laying bird; this report describes the preliminary findings.
Mature egg-laying Japanese quail (Coturnix coturnix japonica) (aged 3–5 months) and chickens (Gallus domesticus) (aged 12–15 months) were maintained on a 10 h dark: 14 h light cycle (05.00 h on; 19.00 h off). Commercial laying diets were fed and drinking water was allowed ad libitum. Blood samples were taken quickly
