Search Results
Search for other papers by J. Th. J. Uilenbroek in
Google Scholar
PubMed
Search for other papers by H. M. A. Meijs-Roelofs in
Google Scholar
PubMed
Search for other papers by P. J. A. Woutersen in
Google Scholar
PubMed
Search for other papers by P. Kramer in
Google Scholar
PubMed
Search for other papers by W. A. van Cappellen in
Google Scholar
PubMed
Search for other papers by L. A. Gribling-Hegge in
Google Scholar
PubMed
Search for other papers by W. J. de Greef in
Google Scholar
PubMed
ABSTRACT
To determine whether the decrease in ovarian 5α-reduced androgen production before first ovulation might be caused by an increase in serum LH, prepuberal female rats were injected at 28–31 days of age with low doses of human chorionic gonadotrophin (hCG) (0·05–0·075 i.u., four times daily). This treatment resulted in ovulation of six to ten ova per rat on day 32 in all animals.
Treatment with hCG resulted in a gradual decrease in ovarian content and production (i.e. content in ovary and medium after 4 h of incubation) of 5α-dihydrotestosterone (DHT) and 5α-androstane-3α,17β-diol. The ovarian content of DHT and the production of 5α-androstane-3α,17β-diol decreased within 24 h after the first injection of hCG. Oestradiol content and production increased between 24 and 48 h after the start of treatment and was maximal on day 31 (day of pro-oestrus).
Activities of 5α-reductase and aromatase were measured in ovarian homogenates obtained on days 29–31. Activity of 5α-reductase in hCG-treated rats was lower than that in control rats on all days studied. Aromatase activity in hCG-treated rats increased between days 29 and 31.
It was concluded that multiple injections of low doses of hCG, which may induce ovulation, cause a decrease in 5α-reduced androgen production, which is probably due to a decrease in 5α-reductase activity. The subsequent increase in oestradiol production corresponds with an increase in aromatase activity. The results indicate that the decrease in 5α-reductase activity as observed in ovaries of spontaneously ovulating rats might be caused by the gradual increase in serum LH, which has been found to occur during the last week before first ovulation.
J. Endocr. (1985) 107, 113–119
Search for other papers by TAKAHIDE MORI in
Google Scholar
PubMed
Search for other papers by HEIGO KOHDA in
Google Scholar
PubMed
Search for other papers by YASUSHI KINOSHITA in
Google Scholar
PubMed
Search for other papers by YOJIRO EZAKI in
Google Scholar
PubMed
Search for other papers by NORIHIKO MORIMOTO in
Google Scholar
PubMed
Search for other papers by TOSHIO NISHIMURA in
Google Scholar
PubMed
Treatment of immature rats with pregnant mare serum gonadotrophin followed by human chorionic gonadotrophin (HCG) caused an acute and temporary increase in concentrations of progesterone, testosterone and oestradiol in plasma with maximum levels 3 h after the administration of HCG.
Concurrent injection of indomethacin and HCG reduced, in a dose-dependent manner, the mean number of ova shed and this was accompanied by a dose-dependent decrease in concentrations of plasma progesterone and testosterone but not of oestradiol when they were measured 3 h after the injection of HCG. The minimum effective dose that blocked ovulation completely at 0 h abolished the acute increase of progesterone and testosterone, suggesting that prostaglandins act on ovulation by stimulating steroidogenesis at an early stage in the preovulatory process. The anti-ovulatory action of the minimum effective dose at 0 h became progressively less potent as the time between injection of HCG and administration of indomethacin was increased, although plasma concentrations of progesterone and testosterone measured at autopsy 18 h after treatment with HCG had not changed appreciably. When indomethacin was administered 10 h after HCG, the relationship between the dose of indomethacin and the mean number of ova differed from that observed when simultaneous injections of indomethacin and HCG were given, and the minimum effective dose that prevented ovulation was much higher than that at 0 h, suggesting that prostaglandins act differently on ovulation in the later stage of the preovulatory process.
It was concluded that prostaglandins may mediate the action of HCG on ovulation through two mechanisms which operate at different stages of the preovulatory process.
Search for other papers by J. BORVENDÉG in
Google Scholar
PubMed
Search for other papers by HELEN HERMANN in
Google Scholar
PubMed
Search for other papers by S. BAJUSZ in
Google Scholar
PubMed
It is well known that administration of a single injection of testosterone propionate to newborn female rats results in permanent anovulatory sterility. After puberty these animals show permanent vaginal cornification and their ovaries contain follicles but no corpora lutea (Barraclough, 1961). One of the most important lesions in these rats seems to be a blockade of the pre-ovulatory discharge of luteinizing hormone releasing factor (LH-RF) from the median eminence.
Porcine LH-RF has been shown to be a decapeptide, pyro Glu-His-Trp-Ser-Tyr-Gly-Leu-Arg-Pro-Gly(NH2), and when this polypeptide was synthesized it was found to have follicle-stimulating hormone releasing factor activity as well (Matsuo, Arimura, Nair & Schally, 1971; Matsuo, Baba, Nair, Arimura & Schally, 1971). In the present experiments we posed the question of whether a subcutaneous injection of synthetic LH-RF could induce ovulation in androgen-sterilized female rats, and if so, whether this would be a dose-dependent effect.
Albino rats of the Sprague—Dawley
Search for other papers by G. S. GREENWALD in
Google Scholar
PubMed
SUMMARY
The oestrous cycle of the hamster is lengthened by 2 to 3 days when 2·5 or 5·0 mg progesterone are injected on day 1 of the cycle (day of ovulation). Antral follicles develop on day 2 but their growth is significantly retarded in progesterone-treated hamsters. Administration of progesterone is followed within 6 h by an abrupt decline in serum FSH and LH concentration but by day 3 the level of FSH is higher than normal. Serum LH is slower to recover in hamsters receiving 5 mg progesterone but normal levels are also restored by days 3 or 4. Increased serum levels of progesterone are maintained until days 3–5 in animals injected with progesterone.
Despite the presence of antral follicles on day 2 and the fairly prompt restoration of normal levels of gonadotrophins, the serum concentration of oestradiol is suppressed for several days in the progesterone-treated hamster. This suggests that progesterone, in addition to affecting the hypothalamic-pituitary system, may also directly inhibit oestrogen secretion by the antral follicles.
Search for other papers by M. E. VELASCO in
Google Scholar
PubMed
Search for other papers by I. ROTHCHILD in
Google Scholar
PubMed
SUMMARY
Factors affecting luteinizing hormone (LH) secretion in response to stimulation of the preoptic area (POA) of the forebrain in rats were explored by determining serum LH levels after electrochemical stimulation of the POA. In rats made anovulatory by exposure to constant light (CLA rats), peak concentrations of LH in serum were found 2 h after stimulation with 5–15 mC, and 1 h after stimulation with 0·5–1 mC. The peak levels increased with increasing doses between 0·5 and 15 mC. The incidence of rats ovulating and the mean number of ovulations/rat were roughly proportional to the stimulating dose, but a plateau was reached between 5 and 10 mC. A threshold level of serum LH seemed to be necessary for ovulation, and the incidence of ovulations of six ova or more/rat increased with the increase in peak serum LH level.
Preoptic-roof section, which cuts dorsal afferents to the POA, enhanced the increase in serum LH in response to POA stimulation in CLA rats, while sodium pentobarbitone anaesthesia decreased the response. In both cases, the incidence of ovulation and the number of ovulations/rat were not different from values found in POA-stimulated control CLA rats showing the same peak serum LH level.
In normal cyclic rats the response of serum LH to stimulation was much greater on the morning of pro-oestrus than on that of oestrus; at prooestrus a second rise occurred between 17.00 and 19.00 h. Three days after ovariectomy the basal level of LH increased; these ovariectomized rats showed a small increase in response to a dose of 5 mC. Treatment with 20 μg oestradiol benzoate at the time of ovariectomy, however, resulted in a lowered basal LH level, but the peak response to 5 mC was almost as great as that found in similarly stimulated intact CLA rats. In intact males and in neonatally androgen-treated females the peak levels of serum LH in response to doses of 5 or 15 mC were equivalent to those in CLA females in response to doses of only 1–5 mC.
Search for other papers by K. BROWN-GRANT in
Google Scholar
PubMed
The administration of testosterone propionate (TP) to female rats during the neonatal period results in a failure of ovulation as adults. Oestrogens also have this effect and it is possible that it is oestrogen produced from an androgenic precursor that normally acts upon the brain in the male rat (Brown-Grant, 1973). In support of this idea McDonald & Doughty (1972) found that the antioestrogen MER 25 (MER) could prevent the failure of ovulation that would otherwise have followed the administration of TP. Their rats were only studied up to 110 days of age, however, and it is known that the anovulatory state may develop later (Gorski, 1971). Also, if oestrogen is the active agent, it is difficult to see why an antiandrogen should protect the animals against the effects of TP administration though it has been suggested (Brown-Grant, 1973) that the agent commonly used, cyproterone acetate (CA), might be effective
Search for other papers by S. Atkinson in
Google Scholar
PubMed
ABSTRACT
Sixteen ewes in mid-seasonal anoestrus were stimulated to ovulate using sequential injections of FSH (total dose 10 mg) over a 4-day period. Half of the ewes received a dietary growth promotant (monensin) known to enhance the ovarian response to exogenous gonadotrophins. The ewes were ovariectomized on day 5 or 11 (day 0 = the initiation of FSH treatment). Serial blood samples were taken in half of the ewes to determine peripheral concentrations of LH and a single sample of ovarian venous blood was collected before ovariectomy. All luteal structures were dissected from the ovaries, counted and incubated in vitro to determine progesterone production. The luteal structures were then examined histologically for the abundance of luteal cells.
The physical appearance of the ovary, along with plasma concentrations of LH and ovarian venous oestradiol indicated that the monensin-treated ewes ovulated before control ewes. The corpora lutea from control ewes produced significantly (P <0·05) more progesterone than did the corpora lutea from the monensin-treated group. Furthermore, only 7% of the remaining luteal structures in the monensin-treated group produced significant amounts of progesterone on day 11, whereas 61% of the luteal structures in the control group were actively secreting progesterone. The mean number of granulosa cells in the follicles was similar at ovulation in the two groups, but the mean numbers of large and small luteal cells were significantly (P <0·05) lower in luteal structures from the monensin-treated ewes than in those from the control ewes. It is therefore postulated that inadequate corpora lutea function following precocious ovulation is due to a lack of luteal cell development formed after premature luteinization.
J. Endocr. (1988) 117, 167–172
Search for other papers by J. Th. J. Uilenbroek in
Google Scholar
PubMed
Search for other papers by P. J. A. Woutersen in
Google Scholar
PubMed
Search for other papers by P. D. M. van der Vaart in
Google Scholar
PubMed
ABSTRACT
Corpora lutea could be identified under the dissection microscope up to 7 days after formation. They were isolated during the oestrous cycle and pseudopregnancy and the progesterone and 20α-OH-progesterone contents were compared with serum values of these steroids. The pattern of progesterone in serum resembled that found in the corpora lutea. However, the pattern of 20α-OH-progesterone concentrations in serum and corpora lutea were different. While 20α-OH-progesterone concentrations in the corpora lutea showed large variations during the cycle, changes in serum concentrations of 20α-OH-progesterone were relatively small. Measurement of hormone concentrations in isolated corpora lutea is therefore a sensitive method for studying corpus luteum activity.
To study whether corpora lutea derived after ovulation of immature follicles showed deficient luteal activity, rats at dioestrus (2 days before pro-oestrus) were induced to ovulate by the injection of 10 IU human chorionic gonadotrophin (hCG) and subsequent luteal activity was studied by measuring hormone concentrations in the corpora lutea on day 5 of pseudopregnancy. Concentrations of progesterone, but not of 20α-OH-progesterone, in corpora lutea derived from follicles induced to ovulate at dioestrusday 1 were significantly lower than those in corpora lutea derived from follicles induced to ovulate at prooestrus. This difference was observed not only when pseudopregnancy was induced by cervical stimulation but also when it was induced by implantation of a pituitary gland under the kidney capsule. However, in the latter case, corpora lutea already present on the day of hCG injection also became activated.
The present experiments demonstrate that by measuring hormone concentrations in isolated corpora lutea changes in luteal activity can be studied effectively. Moreover, it appears that corpora lutea derived from immature follicles contained less progesterone than those derived from fully mature follicles.
Journal of Endocrinology (1989) 120, 325–330
Search for other papers by PUSHPA SETH KALRA in
Google Scholar
PubMed
Search for other papers by L. MARTINI in
Google Scholar
PubMed
SUMMARY
The 'facilitatory' activity of the retroprogesterone derivative 6-chloro-9β,10α-pregna-1,4,6-triene-3,20-dione (Ro 4-8347) on ovulation induced by pregnant mare serum gonadotrophin in immature Sprague—Dawley rats was studied. This retrosteroid is significantly more active in this test than progesterone, dydrogesterone (9β,10α-pregna-4,6-diene-3,20-dione) or chlormadinone (6-chloro-17α-acetoxy-pregna-4,6-diene-3,20-dione).
Search for other papers by L Garcia in
Google Scholar
PubMed
Search for other papers by L Hinojosa in
Google Scholar
PubMed
Search for other papers by R Dominguez in
Google Scholar
PubMed
Search for other papers by R Chavira in
Google Scholar
PubMed
Search for other papers by P Rosas in
Google Scholar
PubMed
The effects of thymectomy performed on 10-day-old (Tx-10) mice on spontaneous puberty and the ovulatory response induced by gonadotrophin treatment were analysed, together with the effects of thymulin replacement from 10 days of age. Infantile thymectomy induced a delay of puberty, a decrease in serum 17beta-oestradiol concentration and a reduced total number of follicles. Injection of thymulin (12 ng/g body weight) to Tx-10 mice resulted in an earlier onset of puberty, a decrease in the weights of ovaries and uterus, and an increase in serum 17beta-oestradiol concentrations. In control and Tx-10 mice, treatment with pregnant mare serum gonadotrophin (PMSG) (5 IU) at 25 days of age resulted in ovulation and the numbers of ova shed by ovulating animals were similar. When the animals were injected with 1 IU PMSG ovulation did not occur. In Tx-10 mice, both 1 and 5 IU PMSG increased the number of follicles to values similar to those observed in the controls. In Tx-10 mice the sequential injection of PMSG (1 IU) and human chorionic gonadotrophin (hCG) (3 IU) resulted in ovulation, but the number of ova shed was lower than in controls. When these animals were injected daily with thymulin, an increase in the number of ova shed and serum 17beta-oestradiol concentrations was observed. The uterine weight of Tx-10 mice was always significantly reduced in response to gonadotrophin treatment. Thymulin injection in PMSG-hCG-treated Tx-10 mice provoked a significant increase in uterine weight. The results suggest that the presence of the thymus after the neonatal period is necessary to normal ovarian development and function. The increase in gonadotrophin-induced ovarian response produced by thymulin replacement indicates that this peptide has a role in this process as one of the connecting signals between thymus and ovaries.
