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SUMMARY
Adult female albino rats were exposed to constant illumination of moderate intensity for 55–65 days; at the end of this period more than 95% had no macroscopically visible luteal tissue in their ovaries and more than 90% were sexually receptive. In these animals ovulation was consistently induced by mating. The major component of the mating pattern responsible for the induction of ovulation was penile intromission. Mounting without intromission was much less effective and the occurrence or non-occurrence of ejaculation did not affect the incidence of ovulation. Non-sexual 'stressful' stimuli or the injection of progesterone also induced ovulation in about 50% of animals. However, adrenal progesterone was not required for either the maintenance of sexual receptivity or mating-induced ovulation since adrenalectomized rats exposed to constant light also mated and ovulated.
The time-course of the secretion of luteinizing hormone (LH), determined by radioimmunoassay of plasma LH, also indicated that mating had effects on LH secretion independent of any action of progesterone. LH concentrations were high at 40 min and maximal at 60 min after mating but decreased thereafter while following the injection of progesterone the levels rose gradually and remained high until at least 360 min after the injection. Sodium pentobarbitone administration had little effect on LH secretion induced by mating but blocked ovulation in some animals. Mating-induced ovulation was not invariably associated with increased activity of the thyroid gland but an increase did occur when the mating stimulus was prolonged.
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SUMMARY
Ovarian follicles develop to the stage where they are competent to ovulate in response to exogenous gonadotrophin at the same rate during early pregnancy as in a normal 4-day cycle in the rat. The length of time during which this competency is retained appears to be shorter than after the blockade of ovulation by pentobarbitone administered at pro-oestrus in rats that are not pregnant. Evidence from oviduct:plasma (O:P) and uterus:plasma (U:P) 131I ratio measurements indicating high progesterone and low oestrogen levels at this stage of pregnancy may be relevant to this finding. Some evidence for a 3-day cycle of follicle development after day 6 of pregnancy was obtained but the high O:P ratios suggest that little oestrogen secretion is associated with this.
Oestradiol benzoate (6·25–100 μg.) administered after day 3 of pregnancy will induce ovulation when competent follicles are present. The thyroid:plasma (T:P) concentration ratio for 131I does not rise in association with ovulation induced by exogenous gonadotrophin. After oestrogen administration, the T:P ratio may increase regardless of whether ovulation is induced or not. The results are discussed in relation to the studies of other workers on the induction of ovulation during pregnancy and to earlier work on the relationship between ovulation and changes in thyroid gland activity.
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Rowlands & Williams [1943] recently reported that the consecutive injection of mare-serum gonadotrophin and chorionic gonadotrophin would cause ovulation in hypophysectomized rats. Serum gonadotrophin was given to stimulate the growth of the atrophic follicles and, subsequently, chorionic and other gonadotrophins containing an excess of the luteinizing hormone were used as a means of causing their rupture. Ova were found in the Fallopian tubes 1–2 hr. after their discharge from the ovaries. Similar experiments have been carried out in the intact immature rat to study, in greater quantitative detail, the optimal conditions necessary for ovulation. A comparative study of the hormonal control of ovulation in different species seemed desirable, particularly on account of the disappointing results that have been frequently reported on the use of mare-serum gonadotrophin in causing ovulation in women.
MATERIAL AND METHODS
Gonadotrophic substances
Two preparations of mare-serum gonadotrophin were used: (1) the International Standard containing 4 International
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ABSTRACT
Circulating progesterone, oestrogens and LH were measured in female marmosets (Callithrix jacchus) over the periovulatory period. Progesterone concentrations increased in all animals within 1 day of the estimated day of ovulation, confirming the usefulness of this hormone for retrospective detection of ovulation. Oestradiol-17β and LH both showed a preovulatory rise, but due to the large quantity of plasma required (oestradiol: 0·2 ml) and the length of time taken for the assay (LH: 2–3 days), measurement of these hormones is not practical for the prediction of ovulation. There were no preovulatory changes in unconjugated oestrone, but a rise in total (i.e. conjugated plus unconjugated) oestrone was used to time the collection of recently ovulated oocytes. Levels of oestrone-3-sulphate showed an increase at least 1 day before the expected day of ovulation in four out of five animals. This preovulatory rise can be measured easily by a rapid direct assay, thereby providing a practical method for predicting ovulation in this species.
J. Endocr. (1984) 103, 17–24
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The ovulation-inducing property of androgens in the laying hen was investigated. In a first experiment, four different androgens were injected subcutaneously into single-comb White Leghorn hens on the day of the last oviposition of a sequence. The hens were killed 10 h later and examined for the presence of an ovum in the oviduct. Testosterone induced ovulation in accordance to the dose injected (median effective dose, 966 ± 193 μg/hen) but the responses to 5α-dihydrotestosterone and 5α-androstane-3α, 17β-diol were not dose-related. The effect of 4-androstene-3,17-dione was more like that of progesterone since it induced ovulation 2 h earlier than the three other androgens.
The physiological significance of the ovulation response to an injection of testosterone was examined in more detail in experiment 2. Seven out of ten hens which were injected with 1 mg testosterone/kg body weight ovulated within 10 h after the injection. Blood samples were taken at hourly intervals and the concentrations of testosterone and progesterone were determined by radioimmunoassay. An injection of testosterone produced an increase in the concentration of testosterone in plasma which was considerably greater and occurred earlier than the preovulatory increase of testosterone in the control birds. The increase in the concentration of progesterone in the hens injected with testosterone was similar in magnitude but occurred earlier than the spontaneous preovulatory increase of progesterone in the control hens. The possible physiological role of testosterone in the ovulation cycle is discussed.
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ABSTRACT
Steroid concentrations were studied in ovarian tissue obtained by means of unilateral ovariectomy during a 10-day period preceding first ovulation. Furthermore, the levels of progesterone were measured in this period in the serum of simultaneous intact control rats.
Ovarian concentrations of testosterone and oestradiol were at about 70 and 15 fmol/mg ovary respectively from 10 to 4 days before first ovulation; they clearly increased to a maximum of 170 and 120 fmol/mg ovary during the last 1–3 days before first ovulation. Ovarian concentrations of 5α-reduced androgens (i.e. androsterone and 5α-androstane-3α, 17β-diol) were high (up to 2500 fmol/mg ovary) from 7 to 4 days before first ovulation, whereas low levels (500–750 fmol/mg ovary) were present during the last 3 days before ovulation. Both ovarian and serum concentrations of progesterone were constantly low (at 500–1000 fmol/mg ovary and at 17–32 nmol/l respectively) from 10 days to 1 day before first ovulation.
An inverse correlation was observed between the ovarian content of 5α-reduced androgens and that of oestradiol, which is in agreement with the existence of a prepubertal shift in pathways of steroid production; this shift seems to take place between 4 and 3 days before first ovulation.
Changes in ovarian steroids on the day of the first pro-oestrus were fully comparable to those at pro-oestrus in adults: relatively high levels of ovarian testosterone and oestradiol, reaching values of 339 and 711 fmol/mg ovary respectively during the morning, an increase in progesterone (from 986 to > 40 000 fmol/mg ovary) first observed at 14.00 h and a decline, observed at 17.00 h, in ovarian testosterone and oestradiol concentration, resulting in values of 9 and 3 fmol/mg ovary respectively at 21.00 h.
J. Endocr. (1984) 100, 281–286
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The present investigation was performed to elucidate the mechanism of the initiation of follicular maturation after inhibition of ovulation in rats treated with pentobarbitone sodium at 13.30 h and progesterone at 14.00 h on the day of pro-oestrus (day 0 denotes the day of these treatments). Ovulation was completely inhibited and the next spontaneous ovulation occurred on day 5, the expected day of the next oestrus. Follicular responsiveness to injection of human chorionic gonadotrophin (hCG) indicated that preovulatory follicles at the time of treatment with pentobarbitone and progesterone regressed by 05.00 h on day 2. Maturation of a new set of follicles began from 17.00 h on day 2 and all rats were induced to ovulate by hCG injection by 17.00 h on day 3, the number of oocytes ovulated being comparable to normal ovulation.
In the animals receiving pentobarbitone sodium and progesterone treatment, two selective rises in plasma FSH, which had peak levels at 05.00 h on day 1 and 11.00 h on day 2, were observed without a rise in LH. Preovulatory surges of FSH and LH occurred on the afternoon of day 4.
These results suggest that the second rise in FSH was induced by regression of Graafian follicles present at the time of treatment with pentobarbitone sodium and progesterone and that this surge of FSH was responsible for initiation of maturation of a new set of follicles destined to ovulate in the subsequent cycle. The mechanism of induction and the role of the first rise of FSH from the night of day 0 to the morning of day 1 cannot be explained at present.
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SUMMARY
During a study of the passage of eggs through the uterine tube of the rabbit, information has been obtained about the time which elapses between an intravenous (i.v.) injection of luteinizing hormone (LH) and ovulation. Eighty-four out of 103 mature does injected with 25 i.u. LH, i.v., ovulated, while nineteen failed to ovulate. Laparotomies were performed at various times from 9 hr. 25 min. to 13 hr. after the LH injection and the number of newly ruptured follicles was counted. Autopsies were performed at intervals of 8–64 hr. after the laparotomy and the number of ovulation points was recorded in the eighty-four does that ovulated. The 'percentage ovulation' was calculated by expressing the number of freshly ovulated follicles counted at laparotomy as a percentage of the number of ovulation points counted at autopsy. This showed no ovulation by 9½ hr., 50% ovulation between
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SUMMARY
Results in 53 llamas (33 mated animals and 20 controls) showed that ovulation is copulation-induced in this species. Ovulation without copulation occasionally occurred during the height of the recognized breeding season in Bolivia.
The first mating during the luteal phase (12–24 days after the preceding ovulation) resulted in ovulation in four out of ten llamas.
Determination of pituitary luteinizing hormone (LH) content showed the highest level on the day before mating (9·00 μg./mg.) and the lowest level on day 4 (6·25 μg./mg.). LH level on day 8 was significantly higher than on day 4 (7·62 μg./mg.). Corpora lutea (c.l.) were well formed on day 4 after mating (408 mg.), reached a maximum size by day 8 (1920 mg.) and rapidly decreased in size to day 16 (136 mg.). The corpus albicans remained as an entity but decreased in size to 21 mg. on day 120. Similar changes were found in c.l. histology and progesterone content. The combined results indicate that the functional life of the c.l. in a non-pregnant llama is 16 days or less.
Treatment with 25 i.u. human chorionic gonadotrophin was sufficient to cause ovulation in 50% of the animals treated.
A large (150 mg.) dose of norethandrolone did not cause morphological regression of the c.l. when measured 5 days after treatment. Treatment with 5 mg. daily for 14 days caused regression of c.l. as compared with untreated controls and animals treated with oestradiol valerate.
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SUMMARY
The ovulation response was measured, by the recovery of tubal ova, in mature dioestrous albino mice after single injections of gonadotrophin, using three preparations of pregnant mares' serum (PMS) and three of human chorionic material (HCG). The dose-response lines were parallel over a limited part of the range, and similar joint action of PMS and HCG was demonstrated within these limits. Higher doses of HCG inhibited ovulation, whereas higher doses of PMS induced superovulation.
The double injection technique (priming followed by ovulating injections) was examined in experiments of factorial design in immature normal and immature hypophysectomized mice. Both PMS and HCG may be used as priming or ovulatory substances in normal mice, though the equivalent doses are different for the two functions. The optimal time interval between priming and ovulatory injections, the effect of time from weaning and the response of two additional strains of mice were also examined.
