Blockade by progesterone of estrogen-induced LH and FSH release in the rhesus monkey

The effect of danazol on gonadotropin secretion during the follicular phase of the menstrual cycle

The effects of danazol on pulsatile luteinizing hormone (LH) release, basal LH and follicle-stimulating hormone serum levels, gonadotropin release induced by estradiol (E2) and gonadotropin-releasing hormone were examined in five eugonadal women. Danazol administration resulted in a significant suppression of follicle-stimulating hormone serum levels. LH concentrations and LH pulse frequency appeared to be reduced, but these changes did not reach statistical significance. The pituitary response to exogenous gonadotropin-releasing hormone was not altered. The stimulatory effect of E2 on LH secretion was completely abolished in one subject, severely diminished in three subjects, and unchanged in one subject. In addition, the time course of this response was altered. Serum prolactin concentrations were lowered, whereas basal E2 and progesterone levels did not seem to be affected.

Why do inadvertent pregnancies occur in oral contraceptive users? Effectiveness of oral contraceptive regimens and interfering factors

Inadvertent pregnancies in combined pill users are not uncommon, and are usually due to errors of tablet taking. However, many factors may contribute to 'pill failure'. In this review the endocrine pharmacology of pill use and the changes reported with missed pills have been considered in detail. The influences of other factors including drug interactions have been reviewed and a series of recommendations made for reducing the risk of pregnancy in each of these circumstances.

The endocrinology of the menstrual cycle: the interaction of folliculogenesis and neuroendocrine mechanisms

(1) The gonadotropins are secreted in a pulsatile fashion in response to the similar pulsatile release of GnRH from neurosecretory neurons centered in the arcuate nucleus of the medial basal hypothalamus. (2) The gonadal steroids appear to exert their feedback effects both directly on the pituitary and through modulation of the pulsatile pattern of GnRH secretion. They may also influence the degree of sialylation and subsequent biologic activity of the gonadotropins. (3) GnRH release is under the control of catecholaminergic neurotransmitters. Norepinephrine appears to act as an excitatory agent, whereas dopamine inhibits GnRH secretion. (4) Dopamine also directly inhibits PRL release and may be the prolactin-inhibiting factor. (5) The endorphins are endogeneous opiate peptides and are derived from a common ACTH/ beta-lipotropin precursor. Through modulation of neurotransmitter mechanisms, the endorphins may affect both PRL and gonadotropin secretion. (6) The catecholestrogens, by virtue of their structural similarity to the neurotransmitters, may mediate the central feedback actions of the gonadal steroids.

Differential response to adrenocorticotropin hormone stimulation in polycystic ovarian disease with high and low dehydroepiandrosterone sulfate levels

The relative contributions of the ovary and the adrenal gland to androgen overproduction in polycystic ovarian disease (PCOD) remain controversial. In this investigation, patients with proven PCOD were divided into two groups, (1) those with low dehydroepiandrosterone sulfate (DHEAS) levels and (2) those with high DHEAS levels, and compared with controls for their response to adrenocorticotropin hormone (ACTH) stimulation. Significant differences in weight, degree of menstrual disturbance, and basal progesterone levels distinguished the two groups with PCOD. Although no discrete enzyme block was unmasked by ACTH, marked differences in steroid production ratios were apparent between the low and high DHEAS PCOD groups. These results suggest that in PCOD with high DHEAS (1) substantial differences in adrenal steroidogenesis pathways occur, (2) increased progesterone as well as inappropriate estrogen feedback may contribute to chronic anovulation, and (3) serum DHEAS levels may be a helpful screen in discerning those patients who have a significant adrenal component to their hyperandrogenism and may benefit from adrenal suppression alone or in combination.

Differential effects of progesterone on secretion of gonadotropic hormones in the rhesus monkey

To obtain new information on the site of the inhibiting actions of progesterone (P) during the follicular phase of the cycle, we administered P continuously to 13 rhesus macaques (Macaca mulatta) from days 5 through 12 of the menstrual cycle. This treatment produced luteal-phase levels (approximately 6 ng/ml of serum) within 4 h. (FSH) concentrations dropped significantly from pretreatment amounts (P less than 0.01). During this time, both immunoreactive luteinizing hormone (LH) (n = 8 animals) and bioactive LH (n = 5) remained stable. The 17 beta-estradiol (E2) concentrations dropped significantly below base line 24 h after treatment (P less than 0.05). The decline in E2 occurred after the decline in FSH. Inhibition of FSH continued for 40 h, after which both FSH and LH rose steadily in a way that resembled a preovulatory surge on days 8 or 9 of the menstrual cycle, and then returned to base line by day 10. When gonadotropins were at their zenith, the ovary did not respond by secreting E2. None of the effects mentioned above were found in control animals treated with blank implants. These data demonstrate that P administered during the follicular phase inhibits FSH but not LH secretion. This initial inhibition probably occurs at a hypothalamic-pituitary site, but after 40 h direct inhibitory effects on the ovary cannot be ruled out. P stimulates the release of gonadotropin in female monkeys despite reduced production of E2 by the ovary.

Rapid recovery of estrogen-induced pituitary gonadotropin surges after luteectomy in rhesus monkeys

In the presence of a functional corpus luteum, positive estrogen feedback on the surge modes of gonadotropin secretion is blocked in rhesus monkeys. We investigated the effects of luteectomy (Lx) on the time required for recovery of pituitary responsiveness (LH/FSH surges) to positive estrogen feedback. Estradiol-17 beta-3- benzoate (EB, 50 microgram/kg sc) was given: 1) 24th prior to, 2) the day of, or 3) 24 h after luteal ablation. Daily measurements of serum follicle stimulating hormone (FSH), luteinizing hormone (LH), estradiol-17 beta (e2) and progesterone (P) were made on each monkey for 5 days. Serum P fell to undetectable levels within 24 h after Lx, whereas E2 levels in circulation peaked within 24h after injection of EB. Among early follicular phase monkeys, this EB treatment results in typical midcycle type LH/FSH surges within 48h. Lx alone was not soon followed by significant changes in pituitary gonadotropin secretion. When circulating P levels were undetectable the pituitary responded fully to EB; that is, typical midcycle type FSH/LH surges occurred. When serum P was in the midst of declining after Lx, gonadotropin surges were present, but attenuated. However, when P levels remained elevated for more than 24 h after EB injection, the surge modes of FSH/LH secretion remained fully blocked. These results demonstrate that the suppressive influence of luteal secretions (principally progesterone) on positive estrogen feedback regulation of the surge modes of pituitary gonadotropin secretion is quite transient in these primates.

Luteinizing hormone-releasing hormone, ovariectomy, and silastic vaginal rings in the Rhesus monkey

The interaction of estradiol and luteinizing hormone-releasing hormone (LRH) may be a critical physiologic mechanism regulating the occurrence of ovulation in many species. These studies were conducted to assess (1) the effects of intramuscular injections of LRH in the intact female rhesus monkey and (2) the effects of estradiol in a Silastic delivery system in ovariectomized female rhesus monkeys. No changes in blood levels of luteinizing hormone (LH) were detected in response to 200 micrograms of LRH. Ovulation did not occur 48 hours after treatment. Ovariectomy decreased estradiol, increased LH, and had no effect on prolactin concentrations in sera. Insertion of a vaginal ring containing 10% estradiol increased blood estradiol levels 100-fold. Serum prolactin levels were unaffected; however, LH concentrations were altered in a multiphasic fashion. After the ring had been in place for 15 days, vaginal blood similar to menstrual flow was observed following removal.

The metabolic clearance rate, head and brain extractions, and brain distribution and metabolism of progesterone in the anesthetized, female monkey (Macaca mulatta)

The brain distribution and metabolism of progesterone were studied in female, rhesus monkeys. Adult monkeys were anesthetized with ketamine and were given a constant infusion of [3H]- or [14C] progesterone. Blood samples were obtained from cannulae inserted into the carotid artery, the jugular vein and lateral (transverse) sinus. The metabolic clearance rate of progesterone was 295 +/- 49 (S.E.) 1/day. The head extraction of progesterone was 30.4 +/- 8.3% (S.E.) and the brain extraction 26.0 +/- 9.18% (S.E.). The peripheral conversion ratios of progesterone to 20alpha-hydroxypregn-4-en-3-one (20alpha-OHP) and 5alpha-pregnan-3,20-dione (5alpha-DHP) were 10.0 +/- 1.3% (S.E.) and 2.4 +/- 0.3% (S.E.), respectively. These same conversion ratios for across the head were 4.8 +/- 1.0% (S.E.) and 1.5 +/- 0.6% (S.E.) and for across the brain 5.0 +/- 0.7% (S.E.) and 2.2 +/- 0.6% (S.E.). The concentration of radioactive progesterone was 2-5 times higher in brain tissues compared to the carotid arterial blood. The tissue concentrations of radioactive progesterone compared to a cerebrum 'control' sample: was lower in the central gray (P less than 0.05); were the same for the amygdala, hippocampus, preoptic-anterior hypothalamus, cerebellum, hypothalamus, thalamus, and anterior pituitary; and were higher in the cervical spinal cord, optic chiasm, mesencephalon, medulla oblongata and pons (P less than 0.1). The distribution pattern of 20alpha-OHP formed from progesterone was similar to that of progesterone. 5alpha-DHP formed from progesterone had a different distribution than progesterone, being highest in the central gray area. High concentrations of 5alpha-DHP were also observed in the mesencephalon, medulla oblongata and hypothalamus and low values in the anterior pituitary. Infusions of [3H]20alpha-OHP and [3H]5alpha-DHP were used to evaluate the in vivo metabolism of progesterone by different brain areas. [3H]Estradiol infused into one monkey had its highest concentration in the anterior pituitary which was 20 times higher than in the carotid arterial blood.