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Search for other papers by MAY REED in
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Search for other papers by W. F. HOUNSLOW in
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SUMMARY
Ovulation has been induced in the cyclic guinea-pig at a time when the ovaries contain mature follicles, by a single injection of purified luteinizing hormone (LH), follicle-stimulating hormone or guinea-pig gonadotrophins from homogenates of female guinea-pig anterior pituitaries. An injection of any one of the substances given too early only caused follicular luteinization and the ova were retained, even with increased dosage. A single injection of LH in mid-dioestrus caused 'LH effects' on the follicles (destruction of the growing follicles), giving a histological picture similar to that which obtains at the time of ovulation in the untreated animal. Homogenates of anterior pituitaries taken from donor guinea-pigs 1–2 days before ovulation was due (but not at any other time in the cycle) when injected into recipients at middioestrus had similar effects on the follicles. Donor anterior pituitaries taken from guinea-pigs in which ovulation had been inhibited by daily injections of progesterone, caused ovulation in recipients with mature ovarian follicles or 'LH effects' in those in mid-dioestrus. It is suggested that in the guinea-pig there is a basal secretion of gonadotrophins during most of the cycle. A day or two before ovulation occurs and when the ovaries already contain ripe follicles, there is a marked increase in the synthesis of LH which is then released from the anterior pituitary gland and rupture of the follicles occurs.
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Search for other papers by H. M. RADFORD in
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Several authors have reported that, in sheep, electrolytic destruction of certain basal hypothalamic regions leads to ovarian inactivity, or failure to exhibit oestrus, or both (Clegg, Santolucito, Smith & Ganong, 1958; Clegg & Ganong, 1960; Radford, 1967). This paper reports the induction of ovulation in sheep by electrical stimulation of the basal hypothalamus. The experimental approach was based on the fact that when ewes are injected with 750 i.u. pregnant mare serum (PMS) on the last day of a course of progesterone injections (10 mg. i.m./day) and 1000 i.u. human chorionic gonadotrophin (HCG) is injected 24 hr. later, ovulation occurs within the next 30 hr., i.e. 54 hr. after PMS (Braden, Lamond & Radford, 1960; Braden & Moule, 1962). If HCG is not injected, ovulation does not occur until later. On the supposition that electrical stimulation of appropriate hypothalamic regions should substitute for HCG, experiments have been done on ewes
Search for other papers by A. P. LABHSETWAR in
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SUMMARY
The effect of a monoamine oxidase inhibitor (MAOI) (mebanazine) given alone or in combination with 5-hydroxy-dl-tryptophan (5-HTP) or dihydroxyphenylalanine (l-DOPA) on spontaneous ovulation was tested in 4-day cyclic rats. Injections of the MAOI or 5-HTP alone, which cause a selective rise in the hypothalamic serotonin level, blocked spontaneous ovulation in 32% and 0% of rats, respectively, and in 73% of rats when given together. By contrast, a combination of MAOI and l-DOPA, which causes a selective rise in the hypothalamic catecholamines, did not block ovulation. A single injection of α-methyl-p-tyrosine, but not of α-methyl-m-tyrosine, blocked ovulation in 100% of rats. These results provide experimental support for the existence of a serotoninergic component in the control of ovulation.
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Search for other papers by J. H. CLARK in
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SUMMARY
Ovulation was blocked in pregnant mare serum-treated immature rats by treatment with chlorpromazine. Reflex ovulation and hence luteinizing hormone release was induced by three procedures: (a) placing male rats with the treated females overnight, (b) mechanical stimulation of the vagina and cervix with a glass rod, and (c) electrical stimulation of the uterine cervix. Mating or mechanical stimulation induced ovulation in 77 and 82% of the rats, respectively. Electrical stimulation was least effective, causing ovulation in only 50%. The average number of ova released and the percentage of rats ovulating was found to be a function of the amount of mechanical stimulation with the glass rod. Pelvic neurotomy abolished the reflex ovulatory response. The stronger response obtained by coitus or mechanical stimuli indicated the possibility of receptor sites in the vaginal wall. This assumption was supported by the finding of penile spines in the rat. A survey of the literature indicates that penile spines are present in a variety of mammalian orders including the primates. The evolutionary relationships and implications of the existence of penile spines and reflex ovulation are discussed. It is suggested that man, like the rat and probably other species which ovulate spontaneously, also has the ability to ovulate after stimulation of the vaginal tract.
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Investigation of hypothalamic areas responsible for release of gonadotrophins in sheep required a method for blocking the natural release of ovulating hormone(s). This report describes the results of preliminary observations on the effect of pentobarbitone sodium on ovulation in the ewe.
In Merino ewes the onset of oestrus was determined by testing with vasectomized rams at intervals of no more than 2 hr. When ewes were found to be in oestrus they were either anaesthetized immediately with pentobarbitone sodium given i.v. and kept anaesthetized for 12, 24 or 48 hr., or anaesthetized for 12 or 20 hr. with pento-barbitone sodium commencing 4 hr. after the onset of oestrus or left conscious as controls. Four of the ewes anaesthetized at the beginning of oestrus were injected intramuscularly with 1000 i.u. human chorionic gonadotrophin (HCG) 6 hr. after the onset of oestrus. The ovaries of some ewes were examined at laparotomy 36
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Search for other papers by P. C. WILLIAMS in
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In the intact rat the intrinsic action of gonadotrophic substances is often complicated by the action of the endogenous gonadotrophins of the test animal. Evidence of such complications is provided by histological differences between the condition of the ovaries of intact and hypophysectomized immature rats when subjected to stimulation by each of a variety of different gonadotrophic substances [Noble, Rowlands, Warwick & Williams, 1939], and by the ability of mare serum gonadotrophin to cause ovulation in intact rats but not in hypophysectomized rats [Rowlands & Williams, 1941]. The ineffectiveness of the serum gonadotrophin in causing ovulation in the absence of the pituitary gland of the test animal may be partly explained by its relative lack of luteinizing activity, but it is also certainly caused, in part, by the atrophic condition of the ovaries when the injection is made [Williams, 1943].
Leonard & Smith [1933] observed that in hypophysectomized rats an
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Search for other papers by A S McNeilly in
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Search for other papers by G R Foxcroft in
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Abstract
The present study was designed to investigate the hormone profiles (oestradiol, LH, FSH, inhibin, progesterone) in high ovulating Meishan sows (MS; n = 9) and in contemporary Large-White hybrid control sows (LW; n = 9) during the follicular phase, the periovulatory period and the early luteal phase. Ovulation rate was higher in MS than LW animals (23·7 and 16·6 respectively; P<0·001) and overall was correlated with the area of the oestradiol peak (P<0·05) and inhibin concentrations (P<0·05). Both the duration of and the area of the oestradiol peak were greater in MS than LW (P<0·01; P<0·02), as were inhibin concentrations both before and after the LH surge (P<0·05). Neither basal nor peak concentrations of LH or FSH differed between the breeds (P>0·05), although FSH concentrations were correlated with the area under the oestradiol peak (P<0·05). Finally, the time-interval from the onset of the LH surge until the rise in plasma progesterone was shorter in MS than LW (54·5 and 74·3 h respectively; P<0·01). In conclusion, these results show for the first time that the higher ovulation rate in MS is associated with enhanced oestradiol and inhibin secretion with no significant difference in LH or FSH concentrations. The more rapid luteinization response to the LH surge by MS in terms of plasma progesterone concentrations may be important in ensuring the high level of embryo survival in this breed.
Journal of Endocrinology (1996) 150, 141–147
Search for other papers by K. J. BETTERIDGE in
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SUMMARY
In rabbits, an anti-pig-luteinizing hormone serum (anti-pig-LH) inhibited coitally-induced ovulation when injected immediately post coitum and this effect persisted for at least 5 days. When administered 90 min after mating, anti-pig-LH had very little inhibitory effect on ovulation and did not prevent the establishment of normal pregnancies. Anti-pig-LH also blocked human chorionic gonadotrophin-induced ovulation in rabbits, evidently by direct cross reaction. Sufficient anti-pig-LH to block ovulation in rabbits inhibited neither ovulation nor conception in four guinea-pigs when injected 0 to 4 days before vaginal opening.
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Maximal levels of progesterone in the plasma after premature ovulation induced by either the administration of human chorionic gonadotrophin (HCG) or LH-releasing hormone (LH-RH) to dioestrous (day 0) rats were observed from 33 to 45 h but decreased 3 h earlier than after spontaneous ovulation. This suggested an earlier decline in the secretory activity of corpora lutea formed from premature ovulations than that of corpora lutea formed during a normal oestrous cycle.
The next spontaneous ovulation occurred 4 days (day 5) after premature ovulation induced by LH-RH on day 0. A single s.c. injection of 2·5 μg oestradiol-17β (OE2) at 10.00 h on day 2 to these animals advanced the next spontaneous ovulation by 1 day. A normal number of oocytes was shed, indicating that earlier secretion of oestrogen on day 2 had advanced the next spontaneous ovulation. A single injection of 2·5 μg OE2 to normal 4-day cyclic rats at metoestrus failed to advance the next ovulation. An earlier decline of progesterone levels in the plasma of rats after premature ovulation as compared with spontaneous ovulation may explain the greater effectiveness of oestrogen in the former group.
The progesterone surge was observed during the period of premature ovulation in both HCG- and LH-RH-treated groups. This progesterone release in the periovulatory period may be responsible for the inhibition of gonadotrophin surges on the expected day of prooestrus (day 1).
