Inhibin and oestradiol-17 beta in antral follicles of various size classes of cyclic rats.

On the various days of the 5-day oestrous cycle of the rat, ovarian antral follicles were dissected out and grouped in five size classes. Four follicles of the same size class were homogenized jointly in medium, after which inhibin-like bioactivity, inhibin immunoreactivity and oestradiol-17 beta content were measured. In general, there was a significant correlation between immunologically and biologically active inhibin levels in the different size classes; overall correlation was 0.

Recombinant FSH (Org32489) induces follicle growth and ovulation in the adult cyclic rat.

The effects of a single injection of recombinant human FSH (rhFSH; Org32489) on ovulation rate and timing and on antral follicle growth were studied in adult 5-day cyclic rats. Rats injected at 1700 h on dioestrus-2 with a dose of 10 IU rhFSH showed, on average, no increase in ovulation rate on the day of expected oestrus. However, an additional, precocious ovulation resulting in a normal number of corpora lutea (13.

Testicular and serum levels of inhibin and expression of inhibin subunit mRNAs are differentially affected by hemicastration in rats of various ages.

Age-related short-term effects of hemicastration on testicular weight, serum FSH, immunoreactive inhibin, LH and testosterone, testicular levels of inhibin subunit mRNA expression, and bioactive and immunoreactive inhibin were studied in rats of 8, 15 and 22 days of age. Hemicastration led to an increased weight of the remaining testis after 24 h in 8- and 15-day-old rats, but not in 22-day-old rats. Serum FSH levels were elevated in all hemicastrated rats after 8 h.

Model of antral follicle dynamics during the 5-day cycle in rats based on measurement of antral follicle inflow.

Antral follicles were counted in ovaries from young adult Wistar rats, collected on the 5 days of the ovarian cycle. Follicles were classified as healthy, early atretic or late atretic and divided into five volume classes. From these data, a model was developed in which the inflow of healthy follicles into the various size classes was quantified.

Prepubertal reduction of the ovarian follicle population by combined LH-releasing hormone antagonist treatment and unilateral ovariectomy influences follicle characteristics but not the ovulation rate at first oestrus.

The effect on first ovulation of the massive reduction of the total pool of ovarian follicles during the infantile and late juvenile period was studied in rats. Treatment with an LH-releasing hormone antagonist (LHRH-A) during infancy (5 mg/kg body weight on days 6, 9, 12 and 15 of life) was combined with unilateral ovariectomy performed on either day 15 (early ULO) or 2-5 days before the expected day of first ovulation (late ULO). Rats were killed on the day of first or second oestrus, when blood was collected and the (remaining) ovaries were prepared for differential counting of follicles and corpora lutea.

The N-methyl-D-aspartate receptor antagonist MK-801 delays the onset of puberty and may acutely block the first spontaneous LH surge and ovulation in the rat.

The physiological role of activated hypothalamic N-methyl-D-aspartate (NMDA) receptors during the final phase of female sexual maturation was explored in the rat. The effects of administration of the specific non-competitive receptor antagonist MK-801 on the occurrence of first ovulation and on LH secretion were studied. Injections of MK-801 (0.

Ovulation rate, follicle population and FSH levels in cyclic rats after administration of an inhibin-neutralizing antiserum.

Ovulation rate, follicle growth, serum FSH and oestradiol concentrations were studied after a single intraperitoneal injection of inhibin antiserum in 5-day-cyclic rats. Control rats received (non-immune) serum from castrated sheep or saline. Rats were injected at 10.

Initial ovulation rate and follicle population after injection of inhibin-neutralizing antiserum in the late-prepubertal rat.

In late-prepubertal female rats passive immunoneutralization of endogenous inhibin was achieved by injection of inhibin antiserum. Effects on follicle population, timing of sexual maturation, ovulation rate at first and second oestrus and serum FSH levels were studied. Rats were injected with antiserum, (non-immune) control serum from castrated sheep (castrated serum) or their IgG fractions, or with saline on day 33 or 3 or 2 days (days -3/-2) before the expected day of first ovulation, day 38.

Effects of a luteinizing hormone-releasing hormone antagonist in late-juvenile female rats: blockade of follicle growth and delay of first ovulation following suppression of gonadotropin concentrations.

Subcutaneous injections of an antagonist against luteinizing hormone-releasing hormone (LHRH-A, Org, 30276) were administered to late-juvenile female rats. The effects on timing of vaginal opening and first ovulation on serum gonadotropin concentrations and on follicle growth were studied. The dose of 100 micrograms LHRH-A/100 g body wt, given on Days 28, 31, and 34, did not influence timing of first ovulation.

Short- and long-term effects of an LHRH antagonist given during the prepubertal period on follicle dynamics in the rat.

The effects of the suppression of the high gonadotrophin concentrations normally present by the end of the second week of life on ovarian follicle dynamics were studied in immature rats. Gonadotrophins were suppressed by treatment with an LHRH antagonist (LHRH-A; Org. 30276) on days 6, 9, 12 and 15, and the total population of ovarian follicles was studied at 15 and 28 days, on the day of first oestrus and on the day of oestrus at or following 90 and 300 days of age.

Advancement of first ovulation by the opioid antagonist naltrexone.

The opioid antagonist naltrexone was administered to female rats during the late juvenile period, and its effects on sexual maturation were studied. Naltrexone treatment (2.5 or 20 mg/kg; four daily injections at 2-h intervals) at 28-32 days of age advanced first ovulation in about 55% of the rats.

Ovarian follicle dynamics in immature rats treated with a luteinizing hormone-releasing hormone antagonist (Org. 30276).

The high concentrations of gonadotropins present in immature female rats by the end of the second week of life were suppressed by treatment with an antagonist against luteinizing hormone-releasing hormone (LHRH-A; Org. 30276) on Days 6, 9, 12, and 15 of life. Differential ovarian follicle counts were made on Days 15, 22, 28, and on the day of first estrus of all growing follicles and follicles greater than or equal to 100 x 10(5) microns 3 (mostly antral).

Effects of treatment with the opioid antagonists naloxone and naltrexone on LH secretion and on sexual maturation in immature female rats.

The effects on sexual maturation of the opioid receptor antagonists naloxone and naltrexone were studied in the female rat. Neonatal treatment (days 1-10) with either naloxone (2.5 mg/kg at 6-h intervals) or naltrexone (20 or 50 mg/kg per day) did not advance sexual maturation as judged by age and body weight at vaginal opening and first ovulation.

Inhibition of first ovulation: administration of an LHRH antagonist to immature female rats.

Subcutaneous injections of an LHRH antagonist (ALHRH; Org.30093) were administered to immature female rats. Neither a single high dose (50 micrograms) nor repeated daily doses of 5-30 micrograms ALHRH/day, administered between 28 and 38 days of age, influenced the age and body weight at the time of vaginal opening or first ovulation.

Periovulatory changes in serum concentration and ovarian content of 5 alpha-androstane-3 alpha, 17 beta-diol in the adult rat.

The high amounts of 5 alpha-androstane-3 alpha, 17 beta-diol (3 alpha-diol) present in immature female rats decline towards first ovulation, but on the day of first proestrus a peak is seen. This raises the possibility that during adulthood similar proestrous peaks may occur. Therefore, serum concentrations and ovarian content of 3 alpha-diol were estimated every two hours between 0900 and 2100 h in adult cyclic rats on the day of proestrus.

Inhibin increases in the ovaries of female rats approaching first ovulation: relationships with follicle growth and serum FSH concentrations.

In order to relate various prepubertal events in a group of 95 late prepubertal female rats, the following data were obtained during the last 10 days before the day of first ovulation: amounts of ovarian inhibin-like activity (ILA) in some animals (n = 47); size and numbers of healthy (antral) follicles with a volume greater than or equal to 100 X 10(5) microns3 (or diameter greater than or equal to 260 microns) present per ovary in their litter-mates (n = 48); serum FSH concentrations in both groups. Rats were unilaterally ovariectomized to obtain an ovary for either estimation of ILA content or for histological procedures and counting of follicles. At the time of unilateral ovariectomy they were bled to obtain serum for estimation of FSH concentrations.

Inhibin-like activity in ovarian homogenates of prepubertal female rats and its physiological significance.

The presence and physiological significance of ovarian inhibin-like activity (ILA) in immature rats was studied by measuring ILA in ovarian homogenates and by studying the short-term changes in serum concentrations of FSH and LH after unilateral or bilateral ovariectomy. Inhibin-like activity in ovarian homogenates was estimated using an in-vitro bioassay system with dispersed rat anterior pituitary cells and subsequent measurement of FSH and LH levels in the spent pituitary cell medium. Inhibin-like activity, expressed in units/ovary, was undetectable in 13-day-old ovaries, was present in 18-day-old ovaries (5.

Changes in ovarian steroidogenesis in prepuberal rats induced to ovulate by low doses of human chorionic gonadotrophin.

To determine whether the decrease in ovarian 5 alpha-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.

Precocious ovulation induced by human chorionic gonadotrophin in the immature female rat: comparison of follicle growth induced by treatment with human chorionic gonadotrophin and by electrical stimulation of the hypothalamus.

Precocious first ovulation, preceded by an endogenous preovulatory LH surge, could be predictably induced in immature female rats by administering repeated injections of human chorionic gonadotrophin (hCG). Administration of a dose of 0.05-0.

Changes in serum concentration and ovarian content of 5 alpha-androstane-3 alpha,17 beta-diol in the female rat approaching first ovulation.

Concentrations of 5 alpha-androstane-3 alpha,17 beta-diol (3 alpha-diol) in serum were estimated in rats bled once during a 10-day period preceding first ovulation; ovarian contents of 3 alpha-diol were estimated over the same period. Serum values of 3 alpha-diol, measured at 1100 h, showed a significant decrease towards first ovulation; there was good correlation (r = 0.78; n = 10) between mean serum and ovarian concentrations.

Compensatory ovulatory mechanisms operative after first ovulation in rats unilaterally ovariectomized prepubertally.

Ovarian steroid contents and serum concentrations of luteinizing hormone (LH), follicle-stimulating hormone (FSH) and prolactin were measured during the days after first ovulation in rats unilaterally ovariectomized in late prepuberty. In addition, follicle counts were made at second estrus and second metestrus. During the cycle following first ovulation, ovarian estradiol contents in unilaterally ovariectomized (ULO) rats were significantly increased as compared to intact rats on the day of metestrus, on diestrus 1 and on second estrus.

Ovarian steroid concentrations in rats approaching first ovulation.

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.

Changes in serum concentration of luteinizing hormone in the female rat approaching puberty.

Concentrations of LH in the serum were estimated in rats bled either once or twice during a 15-day period preceding first ovulation. In rats bled once (between 09.00 and 17.

Ovarian steroid concentrations in rats with spontaneous and with delayed or advanced ovulation.

The present study examined the ovarian progesterone levels in rats during the normal 5-day oestrous cycle and in rats with an experimentally induced delayed or advanced ovulation. Ovarian androgen and oestrogen concentrations were also studied in rats with an advanced ovulation. The ovarian progesterone concentrations during the normal cycle showed two peaks: one during metoestrus and dioestrus 1 and the second during the afternoon of pro-oestrus.

Developmental patterns of levels of corticosterone and of corticosterone binding in the serum of female rats: effects of ovariectomy and adrenalectomy.

Corticosterone concentrations and corticosterone binding in the serum were studied in immature female rats, using radioimmunoassay and batchwise gel equilibrium techniques. A parallel developmental pattern was found for corticosterone levels and its serum binding with a neonatal drop, followed by low levels until 12 days of age and a rise between 12 and 28 days of age. Effects of adrenalectomy, of ovariectomy, of the combined operation and of sham-operations, performed at various ages, were also studied.