Incidence Of Ovulation Research Articles

INFLUENCE OF ADRENORECEPTOR AGONISTS AND ANTAGONISTS ON OVULATION IN THE RABBIT OVARY PERFUSED IN VITRO

Ovaries from sexually mature virgin rabbits were dissected free on both sides and cannulated in situ via that part of the aortic segment supplying the ovarian arteries. The ovaries were mounted in a closed, recirculating perfusion system for oxygenation in vitro. Ovulation was induced by human chorionic gonadotropin (hCG) given either i.v. (100 IU) or directly into the perfusion medium (20 IU). Follicular ruptures occurred in 42 out of a total of 54 ovaries. The in vivo route of hCG administration was found to be most efficient, with ovulations occurring after a mean of 11.5 h, which corresponds well with the incidence of ovulations in situ. The prostaglandin synthesis inhibitor, indomethacin, totally abolished the hCG-induced ovulations. beta-Adrenoreceptor stimulation in vitro with terbutaline or with noradrenaline in the presence of alpha-receptor blockade with phenoxybenzamine caused a significantly increased number of gonadotropin-induced ovulations. Phentolamine or phenoxybenzamine given alone reduced the number of ruptured follicles. Noradrenaline (in the absence of hCG) and clonidine augmented the incidence of ovulation. The results indicate that local adrenoreceptor mechanisms participate in the process of ovulation, both via alpha-adrenoreceptors (probably affecting the follicular smooth musculature) and beta-adrenoreceptors (possibly through some trophic or endocrine mechanism other than a mechanical factor).

Corpora lutea with a short life-span induced by rams in seasonally anovulatory ewes are prevented by progesterone delaying the preovulatory surge of LH

Seasonally anovulatory Merino ewes isolated from rams were allocated to three treatments before the re-introduction of rams. Ten ewes received a single injection of progesterone (20 mg), 18 ewes received the injection of progesterone but had the ram-induced preovulatory surge of LH replaced by a series of injections of GnRH 24 h after the introduction of the rams, and 20 control ewes had no hormone treatment. Of the 48 ewes, 44 ovulated within 5 days of the introduction of rams and the treatments had no significant effect on the incidence of ovulation. The frequency of corpora lutea with a short life span (the interval between successive preovulatory surges of LH being 5.1 +/- 0.9 days) was 72% for control ewes and 58% for ewes treated with progesterone and GnRH, but such CL were prevented completely after the injection of progesterone alone (P less than 0.001). The injection of progesterone also delayed the preovulatory surge of LH (P less than 0.001). These results suggest that progesterone assures normality of corpora lutea by lengthening the period of gonadotrophin priming of follicles before ovulation.

4 - Ovulatory Disorders in Women with Polycystic Ovary Syndrome

With the use of pelvic ultrasound imaging we have found that more than half of the women presenting to our clinic with ovulatory disturbances have polycystic ovaries. As a group hirsutism is common, the serum LH, the LH:FSH ratio and serum androgen levels are higher than in other groups of patients with anovulation, but many of the women we studied were non-hirsute and had normal levels of these hormones. The aetiology of PCOS remains obscure and there is probably more than one cause. Disturbance of hypothalamic/pituitary, ovarian or adrenal function could all result in the development of polycystic ovaries. Our own data, based on pelvic ultrasound and measurement of serum androgen levels, suggest that an ovarian abnormality, other than the obvious morphological one, may be identified in most women although this does not prove (except perhaps in those women with unilateral PCOS) that the ovary is the primary site of the disturbance. Management of ovulatory disturbances includes symptomatic treatment of dysfunctional uterine bleeding and induction of ovulation. Although the ovulation rate following clomiphene is quoted as about 75%, this is probably an overestimate; less than half the 'ovulators' become pregnant and in those who do there is a high risk of early pregnancy loss. Induction of ovulation in clomiphene non-responders remains a difficult problem. The results of ovarian wedge resection are variable and any beneficial effect is short-lived with the risk of long-term infertility due to pelvic adhesions. Laparoscopic electrocautery may be a useful alternative, but it is too early to assess this form of treatment. Of the medical methods of ovulation induction in clomiphene non-responders, two methods have emerged as being highly promising: the first is administration of HMG following suppression of the pituitary by an LH-RH analogue; so far only a very small number of patients have been treated. The second is low-dose FSH. Initial studies, including our own, have shown a high incidence of ovulation and a pregnancy rate of 50%.

Semen-induced ovulation in the bactrian camel (Camelus bactrianus).

Bactrian camels (63 female female, 8 male male) were used in the breeding season to determine the factors that will induce ovulation. After insemination of semen samples into the vagina, the ovaries were checked for ovulation by rectal palpation. The results indicated that ovulation was induced by the seminal plasma, but not by the spermatozoa, and the incidence of ovulation after insemination was 87%. Most of the females (66%) had ovulated by 36 h after insemination and the rest by 48 h, as after natural service. The least amount of semen required to elicit ovulation was about 1.0 ml. Intramuscular injections of LH, hCG and LHRH also caused ovulation, even in females that had not ovulated in response to insemination.

Effects of an agonist of gonadotrophin releasing hormone in cattle. I. Hormone concentrations and oestrous cycle length

Four trials were completed to study the effects of a single intramuscular injection of 5 μg of an agonist of gonadotrophin releasing hormone (Hoe 766) on plasma concentrations of LH and progesterone, and on oestrous cycle length in normally cycling dairy cows. The first trial (four cows) showed that a mid-cycle injection of Hoe 766 temporarily increases plasma LH from less than 5 ng/ml to over 20 ng/ml within 2.5 h. Average plasma progesterone concentrations ranged from 4.8 to 7.0 ng/ml compared to 3.3 ng/ml in the control animal. The second trial (22 cows) showed that an injection of Hoe 766 on Cycle Day 3, 6 or 9 (Oestrus = Cycle Day 0) increased average plasma progesterone concentrations during Cycle Days 13, 14 and 15 by 1.2 ng/ml. Each of three cows injected on Cycle Day 16 maintained plasma concentrations above 3.9 ng/ml until Cycle Day 19 and corpus luteum (CL) size was maintained until Cycle Day 21. Except for the group of cows injected on Cycle Day 3, all other groups had temporarily reduced concentrations of plasma progesterone when sampled 24 h after Hoe 766 administration. The third trial (216 cows) showed that a single injection of Hoe 766 made between Cycle Day 1 and 10 did not alter oestrous cycle length (21.5 vs 21.3 days). In contrast, in the fourth trial (371 cows), a single injection of Hoe 766 between Cycle Days 12 to 16 altered the distribution of cycle lengths of 17–29 days, the average cycle length and the incidence of ovulation without detected oestrus. Compared to matched control cows, fewer Hoe 766-treated cows were detected in oestrus (73.9% vs 90%), or had cycle lengths of less than 20 days (4.7% vs 22.2%). These effects were most pronounced among cows injected on Cycle Day 16 when only 51.7% were detected in oestrus and their average cycle length was 24.1 days. These effects were not due to the formation of a secondary CL. Rather, the injection of Hoe 766 stimulated CL function and appeared to prevent or delay normal luteolysis when administered from Cycle Day 12.

High incidence of ovulation in menstrual cycles following estrogen treatment for tall stature: endocrine and sonographic studies

Journal Article High incidence of ovulation in menstrual cycles following estrogen treatment for tall stature: endocrine and sonographic studies Get access R P Willig, R P Willig Universitäts-Kinder Search for other works by this author on: Oxford Academic Google Scholar K Bonorden, K Bonorden Universitäts-Kinder Search for other works by this author on: Oxford Academic Google Scholar T Riebel, T Riebel Universitäts-Kinder Search for other works by this author on: Oxford Academic Google Scholar N Stahnke, N Stahnke Universitäts-Kinder Search for other works by this author on: Oxford Academic Google Scholar W Braendle W Braendle Universitäts-KinderFrauen-Klinik, Hamburg-Eppendorf Search for other works by this author on: Oxford Academic Google Scholar Acta Endocrinologica (Norway), Volume 110, Issue 1_Supplement_a, Apr 1979, Pages S104–S105, https://doi.org/10.1530/acta.0.109S104 Published: 01 April 1985

Dose-response relationship between dose of clomiphene citrate and incidence of ovulation.

AbstractOne hundred and fifty anovulatory, infertile women were treated with clomiphene citrate in an individualized, graduated therapeutic regimen. Women with high serum follicle stimulating hormone or prolactin concentrations were not included. Ovulation was induced in 135 (90.0%) of the 150 women. Of the 55 women who achieved pregnancy, 50 (90.9%) did so at a dose of 150 mg for 5 days or less. Five pregnancies (9.1%) were achieved with higher doses. There was a significant correlation between the total dose of clomiphene citrate administered per cycle and the cumulative incidence of ovulation. There was also a significant relationship between the total dose of clomiphene per cycle and the cumulative incidence of pregnancy.

Reduction of central epinephrine concentrations is consistent with the continued occurrence of ovulation in rats treated with an inhibitor (LY 134046) of phenylethanolamine N-methyltransferase.

Groups of 4-day cyclic rats were injected (i.p.) with LY 134046 (50 mg/kg), a central inhibitor of phenylethanolamine N-methyltransferase, or saline at 09.00, 13.00 and 19.00 h on the day of proestrus. The incidence of ovulation was examined the following estrous morning. There was no difference in the number of ova in drug-treated animals compared to saline-treated controls. In other groups of 4-day cyclic rats, LY 134046 or saline was injected daily at 10.00 h for 5 consecutive days from proestrus to proestrus inclusive. The animals were decapitated the following day and ova were counted. Epinephrine concentrations were determined by radioenzymatic assay in the mediobasal hypothalamus (MBH) and the medial preoptic area (MPOA). All saline-treated controls and 10/14 of the drug-treated animals had ovulated, while epinephrine concentrations in the MBH and MPOA had been reduced by 95.8 and 94.7%, respectively, compared to saline-treated controls. These experiments suggest that a significant surge of luteinizing hormone occurs to initiate ovulation even after a severe reduction in central epinephrine concentration has taken place.

Treatment of anovulatory patients by pulsatile administration of gonadotropin releasing hormone

83 anovulatory patients refractory to clomiphene were treated with gonadotropin releasing hormone (GnRH) in pulsatile form (Zyklomat). 146 of 172 treated cycles were ovulatory. A total of 37 pregnancies occurred. The patients were classified into three groups according to the degree of severity of their cyclic disturbance and according to the results of testosterone determinations. In amenorrhoic women with normal testosterone values (group I) the authors found the highest incidence of ovulation and pregnancies. In the patients of group II the ovulation rates were high, whereas the incidence of pregnancies was low (this group comprised anovulatory oligomenorrhoea and normal testosterone values). It was found that about 30% of the anovulatory women with elevated testosterone levels (group III) were refractory to therapy, the proliferation phases being mostly considerably prolonged during the ovulatory cycles. It is concluded from the results of this study that in women with normoandrogenemic amenorrhoea the treatment of first choice should be pulsatile application of GnRH. In many hyperandrogenemic, anovulatory patients treatment with gonadotrophins should be considered as the presently more suitable method.

Plasma estradiol and progesterone levels during post partum ovulation and early pregnancy in the common marmosetCallithrix jacchus

The incidence of ovulation and subsequent pregnancy in post partum marmosets were studied. By two weeks following delivery, all the animals (N=10) had ovulated as determined by a gradual rise in plasma estradiol followed by a rise in plasma progesterone (p>31.8 nmol/l) levels. The mean day of ovulation was 11.3±1.5 (9–14 days). Eighty percent of these females became pregnant as indicated by a continued rise in plasma progesterone levels (p>127 nmol/l) and as confirmed by transabdominal uterine palpation. These results suggest that the day of delivery could serve as a useful parameter to monitor ovulation and pregnancy in this non-menstruating primate species.

The effects of chlorpromazine, mianserin and Org GC94 on reproductive function in the rat.

In the assessment of drug safety with respect to mammalian reproductive function chlorpromazine and two serotonin antagonists, mianserin (Org GB94 ) and Org GC94 were studied for their effects on ovulation and ovum transport. In addition, the effect of coitus on drug-induced ovulation inhibition was investigated. The compounds were intragastrically administered to Charles River CD rats in a single dose or in consecutive daily doses for one or two weeks. The incidence of ovulation and the number of eggs were recorded. The compounds blocked ovulation in pro-oestrous rats after a single dose. Ovulation was restored by coitus in drug-treated animals. The compounds appeared to become less effective in blocking ovulation after multiple dosing. No effects on ovum transport were detected. From the results obtained in this study, it is concluded that the CNS-active drugs investigated did not adversely affect reproductive function in the rat.

Ovulatory and steroidal responses in the lamprey following administration of salmon gonadotropin and agonistic and antagonistic analogues of gonadotropin-releasing hormone

Hormone injection experiments were conducted for 2 years during the spring when adult Petromyzon marinus returned to a freshwater stream to spawn. Successive injections of salmon gonadotropin and synthetic analogue of hypothalamic GnRH (gonadotropin-releasing hormone) advanced ovulation by 2 to 3 weeks in the tests of the 1 st year. Such treatment in the doses used also elevated plasma estradiol levels almost threefold above those of untreated females prior to ovulation. A more extensive 2nd year experiment had essentially similar results, though the experiment was complicated by the delaying effects of an extended period of low ambient water temperatures. At temperatures which permitted eventual ovulation, either salmon gonadotropin or active GnRH in a dose-related manner advanced ovulation by at least several weeks. However, even in the extended period preceding ovulation, at low temperatures either salmon gonadotropin or GnRH injections elevated plasma estradiol levels in a dose-related and time-related manner. Injections of another analogue of GnRH, which in mammalian tests is a competitive inhibitor of GnRH, had little or no effect either on plasma estradiol levels or on incidence of ovulation. These results indicate that there may be hypothalamic control over pituitary and gonadal function in lampreys.

Effects of Photoperiod on Puberty Attainment of Female White-Tailed Deer

Sixteen female white-tailed deer fawns (Odocoileus virginianus) were hand-reared in lightcontrolled chambers to evaluate the effects of photoperiod on the onset of puberty. Fawns raised on 16 hours light and 8 hours dark (16L-8D) were paired by weight at approximately 4 months of age (16 Oct) and randomly divided between 2 treatments. Treatment I was changed to 8L-16D on 16 October and Treatment II was changed to 8L-16D on 5 December. Timing of pelage change, changes in growth rate, and onset of puberty were affected (P < 0.05) by the initiation of the 8-hour day. Similar time-related physiological responses were observed for both treatments immediately following the start of the short (8-hr) day. J. WILDL. MANAGE. 47(3):595-604 Regional variation in white-tailed deer fawn productivity rates has been observed in many states. Michigan is no exception, with fawn productivity rates (fetuses per doe) of 0.65 in Region III (41030'-43031'N latitude) and 0.07 in Region I (45?30'47030'N) (Friedrich and Burgoyne 1980). Regional variation in range quality has been shown to influence productivity and onset of puberty in white-tailed deer in New York (Cheatum and Morton 1946, Cheatum and Severinghaus 1950), Wisconsin (J. B. Hale, unpubl. rep., Wis. Conserv. Dep., 1959), and Missouri (W. Porath, pers. commun.). Range quality is usually estimated by an area's deer fertility level in conjunction with indirect measures of topography, climate, vegetative cover, and soil (Cheatum and Severinghaus 1950). Other factors that affect fertility, besides range quality, also have been proposed. Ransom (1967) studied 3 areas of estimated high adult doe fertility and range quality in southern Manitoba and concluded that differences in fawn fertility rates were not due to the available food supply, but instead were due to only a few fawns being able to develop sexually before weather conditions retarded growth and development. Abler et al. (1976) noted that neither protein level nor energyprotein interaction had any significant effect on mean plasma progesterone level, which was used as an indication that ovulation had occurred. However, the level of protein may have affected the incidence of ovulation and puberty in fawns given high-energy diets. A study of precocious puberty in Columbian black-tailed deer (Odocoileus hemionus columbianus) showed no simple threshold effect of weight on attainment of puberty (Mueller 1977). Apparently, precocious puberty in fawns is not caused by only 1 factor, but is the result of an interaction of many factors. Changing photoperiod has been shown to elicit many physiological and behavioral responses, such as timing of reproductive cycles (McDowell 1970), antlerogenesis, and pelage changes (French et al. 1960). The objective of this study was to investigate the effects of different photoperiods on the onset of puberty in whitetailed deer fawns. I thank C. Bennett, L. Swanson, S. Schmitt, T. Cooley, A. TuckJ. Wildl. Manage. 47(3):1983 595 This content downloaded from 207.46.13.124 on Wed, 22 Jun 2016 05:23:35 UTC All use subject to http://about.jstor.org/terms 596 PHOTOPERIOD EFFECTS ON FEMALE WHITE-TAILED DEER * Budde er, G. Burgoyne, E. Langenau, R. Aho, J. Stuht, D. Ullrey, and J. Wickham for assistance in the completion of this study.

The Effect of an Equatorial Light Environment on Reproduction in Sheep. I. The Breeding Season

Various aspects of the breeding seasonality of Welsh Mountain (WM), Border Leicester (BL), North Country Cheviot (NCC) and Scottish Blackface (SBF) ewes were investigated during two breeding seasons in housed and field ewes in the local light (LL) environment of Potters Bar (lat. 51°43′N) and in ewes housed in a simulated equatorial light environment (EL) (13L: 11D). Significant advancement of the onset of oestrous periods was observed in all breeds maintained in the EL environment and resulted in a rephased and shorter breeding season. Advancement varied according to breed and was greater in WM (62 days) and BL (42 days). There was no significant difference between NCC (30 days) and SBF (28 days) ewes. The level of oestrous activity in a breed over a sequence of 17-day periods and the duration of oestrus tended to be reduced in EL ewes. In the EL environment NCC and SBF ewes had significantly lower mid-cycle progesterone concentrations than ewes of the same breed in the LL environment. There was also a higher incidence of ovulation without oestrus and oestrus without ovulation in the EL environment. The plasma progesterone concentration at various stages of pregnancy did not show a significant difference between light environments. Plasma progesterone concentration on day 17 after mating had an accuracy of 92·5% as a diagnosis of pregnancy. The value of plasma progesterone determinations in the study of seasonal reproductive activity is discussed.

Hypophysiotropic signal frequency and the functioning of the pituitary-ovarian system in the rhesus monkey.

In adult rhesus monkeys bearing hypothalamic lesions that abolished secretions of LH and FSH, normal circulating levels of these hormones and consequent follicular development culminating in ovulation were reestablished by the administration of a GnRH pulse once every hour (control frequency). We examined the effects of slowing the frequency of these pulses on ovarian follicular development, as assessed by circulating concentrations of estradiol. A reduction in frequency to one pulse every 90 min supported follicular development in most instances, albeit with a diminished incidence of ovulation. One pulse of GnRH every 2 h resulted in anovulatory follicular cycles with lower peak concentrations of estradiol than those achieved on the control frequency. Follicular development was absent when GnRH pulses were delivered once every 3 h. When mean concentrations of gonadotropins were determined during periods of low circulating estradiol levels, plasma FSH concentrations in monkeys receiving GnRH pulses at the slow rates did not differ from control, whereas LH concentrations were significantly reduced. It can be concluded that small reductions in the frequency of GnRH stimulation have profound effects on the quality of follicular development, even when FSH concentrations are maintained at normal levels.

Incidence of ovulation in the years after the menarche.

Urine for the analysis of pregnanediol was collected weekly for 3 months from 209 menstruant women aged 11-24 years who lived with their parents and from 59 women aged 17-23 years who had left the parental home. Menstrual cycles were classed as ovulatory if the 24-h pregnanediol output in the 12 days preceding menstruation was greater than or equal to 5 mumol on a single occasion or if the total excreted on 2 days, 1 week apart, was greater than or equal to 7 mumol. In the first group, ovulatory incidence increased with menarchal age. Unfailing ovulation occurred in 22.9, 25.0, 44.8, 42.9, 63.2, 71.8 and 82.6% of those who were less than 1, 1- less than 2, 2- less than 3, 3- less than 4, 4- less than 5, 5-8 and 9-12 years from menarche. Comparable figures for the women who lived in flats and hostels were 40.0% (menarchal age, 5-8 years) and 78.6% (9-12 years). It is concluded that a regular pattern of ovulatory menstrual cycles is established in most young women within 5 years of the menarche, and that departure from the family home is often associated with a regression to a juvenile pattern of anovulatory menstrual cycles.

Blockade of the preovulatory release of gonadotropins and prolactin by spinal transections in female rats.

The effect of spinal transections on the preovulatory release of gonadotropins and PRL was investigated in female rats. A preovulatory rise in serum LH, FSH and PRL and subsequent ovulation were prevented by complete spinal transections (CST) at high thoracic levels (T3-T7), but not at low thoracic and lumbar levels (T8-L5), performed at 1000-1230 h on proestrus. Norepinephrine (NE) concentrations in the preoptic-anterior hypothalamic area at 1700-1800 h on proestrus were also significantly reduced by CST at high thoracic levels, but not at lumbar levels. Either electrochemical stimulation of the suprachiasmatic part of the preoptic area or NE injection into the third ventricle at 1400-1500 h on proestrus restored ovulation in animals with CST at high thoracic levels. Animals with CST at lumbar levels exhibited relatively regular 4-day cycles, but those with CST at high thoracic levels showed prolonged periods of diestrous (8-20 days) before they resumed cyclicity. In the case of partial transections, bilateral transections of the lateral columns, but not transections of the dorsal or medial columns, of the spinal cord at T4-T5 significantly blocked the preovulatory gonadotropin release and the occurrence of ovulation. Unilateral transections of the lateral columns of the spinal cord or unilateral electrolytic lesions of the ventrolateral part of the medulla oblongata (VLMO) failed to block ovulation. When combinations of them were performed ipsilaterally, ovulation occurred, but when they were performed contralaterally, the incidence of ovulation was significantly decreased.(ABSTRACT TRUNCATED AT 250 WORDS)

Ovarian responses of anoestrous goats to stimulation with pregnant mare serum gonadotrophin

Ovulation has been induced in feral goats before the onset of the breeding season by treatments with pregnant mare serum gonadotrophin (PMSG) combined with a synthetic progestagen (6α-methyl-17α-acetoxyprogesterone) administered via intravaginal pessary. Four hundred I.U. PMSG induced mean ovulation rates of 2–3 follicles per doe, whether administered at the same time as, or 2 days before, removal of the progestagen pessary. One-thousand I.U. PMSG was slightly more effective in inducing ovulation, but this was accompanied by a highly variable degree of stimulation of excessive numbers of follicles which occasionally luteinized but did not ovulate. There was a high correlation between the number of large unovulated follicles and the serum levels of oestradiol-17β observed around the time of ovulation in animals on the 1000 I.U. PMSG dosage. In these animals, oestradiol levels remained high throughout the early luteal phase, reaching maximal values at 7 days after PMSG administration. Copora lutea were not maintained in animals which ovulated following administration of PMSG 2 days before progestagen withdrawal. Administration of 250 I.U. human chorionic gonadotrophin (HCG) at the onset of oestrus failed to improve ovulation rates following 1000 I.U. PMSG or to decrease incidence of large unovulated follicles. Administration of 50 μg luteinizing hormone-releasing hormone (LH-RH) at the onset of oestrus significantly decreased the incidence of ovulation, and markedly increased the incidence of large unovulated follicles observed at laparotomy.

Hypothalamo-hypophyseal sensitivity to hormones in the hen. II. Plasma concentrations of LH, progesterone, and testosterone in response to peripheral and central injections of LHRH or testosterone.

Experiments were conducted to investigate changes in plasma LH, progesterone (P4), and testosterone (T) and the incidence of premature ovulation in response to peripheral and central injections of T or synthetic LHRH administered 14–12 h prior to the first ovulation in a sequence. Injection of 2.0 mg T (i.m.) induced premature ovulation in four of five hens. Plasma concentrations of LH and P4 in T-injected hens, compared with corresponding values from control hens, were significantly increased in all five birds by 90 min and reached highest concentrations by 180 and 240 min, respectively, following injection. Plasma T was increased to 19.88 ± 3.40 ng/ml (SEM) 30 min following injection of 2.0 mg T and slowly declined throughout the remaining sampling interval. There was no significant (P>0.05) dose relationship with respect to premature ovulation between 10.0 and 80.0 μg of centrally injected T. In an experiment in which hens served as their own controls and in which the control (vehicle) and 20 μg T intraventricular injections were assigned at random to each hen, T did not affect the incidence of ovulation or concentrations of plasma LH or P4, but plasma T concentration was increased significantly by the first sampling period (30 min) after injection, suggesting some leakage of T from the site of injection into the peripheral circulation. Four of the five hens injected i.v. with 20 μg LHRH responded with significant elevations in plasma LH, P4, and T by the first sampling period after injection and with premature ovulation. Analysis of data from hens injected centrally with doses of LHRH from 0.001 to 5.0 μg revealed a significant dose-response regression (P<0.01) with an ED50 of 0.53 μg. Five of six hens injected centrally with 5 μg LHRH responded with a premature ovulation, and all six treated birds showed increased plasma concentrations of LH, P4, and T within 30 min of the time of injection, compared with values obtained in vehicle-injected birds. We conclude that peripheral injections of unphysiologically high doses of T are capable of inducing premature ovulation, but that this effect is not mediated by T at the site of the hypothalamo-hypophyseal axis. In addition, LHRH injected i.v. or centrally 14–12 h prior to the first ovulation in a sequence is capable of inducing significant and sustained release of LH, P4, and T and premature ovulation.

Incidence of ovulation in young women—a comment

Comments on a recent article in which a much higher incidence of anovulatory menstrual cycles among women under age 25 than among older women was recorded, an observation that appeared to conflict with other data suggesting that women reach peak fertility between 20-25. The conclusion was that young women reach peak maximum fertility before their peak ovulatory efficiency. The author notes that the possibility that such an age distribution of anovulatory cycles could also be caused by a cohort effect was overlooked. The elevated incidence of anovulation could be due to an environmental change that affected recent cohorts more than earlier ones. Such effects have not been uncommon. Western populations in this century have experienced major epidemics of lung and breast cancer and cardiovascular disease, and postwar cohorts have also suffered apparent deterioration in semen parameters and a large increase in stilbestrol induced reproductive disorders. Cohort effects have been seen as real and important features of 20th century biology. Further studies are needed to determine the validity of the age distribution, and, if corroborated, several tests should be performed to distinguish between the 2 interpretations, including prospective studies and studies in less developed societies.