Effects of various progestational preparations on gonadotropin secretion in ovariectomized immature female rats

Hirsutism, virilism, polycystic ovarian disease, and the steroid-gonadotropin-feedback system: a career retrospective

This career retrospective describes how the initial work on the mechanism of hormone action provided the tools for the study of hirsutism, virilism, and polycystic ovarian disease. After excessive ovarian and or adrenal androgen secretion in polycystic ovarian disease had been established, the question whether the disease was genetic or acquired, methods to manage hirsutism and methods for the induction of ovulation were addressed. Recognizing that steroid gonadotropin feedback was an important regulatory factor, initial studies were done on the secretion of LH and FSH in the ovulatory cycle. This was followed by the study of basic mechanisms of steroid-gonadotropin feedback system, using castration and steroid replacement and the events surrounding the natural onset of puberty. Studies in ovariectomized rats showed that progesterone was a pivotal enhancer of estrogen-induced gonadotropin release, thus accounting for the preovulatory gonadotropin surge. The effects of progesterone were manifested by depletion of the occupied estrogen receptors of the anterior pituitary, release of hypothalamic LHRH, and inhibition of enzymes that degrade LHRH. Progesterone also promoted the synthesis of FSH in the pituitary. The 3α,5α-reduced metabolite of progesterone brought about selective LH release and acted using the GABA(A) receptor system. The 5α-reduced metabolite of progesterone brought about selective FSH release; the ability of progesterone to bring about FSH release was dependent on its 5α-reduction. The GnRH neuron does not have steroid receptors; the steroid effect was shown to be mediated through the excitatory amino acid glutamate, which in turn stimulated nitric oxide. These observations led to the replacement of the long-accepted belief that ovarian steroids acted directly on the GnRH neuron by the novel concept that the steroid feedback effect was exerted at the glutamatergic neuron, which in turn regulated the GnRH neuron. The neuroprotective effects of estrogens on brain neurons are of considerable interest.

Regulation of the preovulatory gonadotropin surge by endogenous steroids

Estradiol secreted by growing ovarian follicle(s) has been considered classically to be the neural trigger for the preovulatory surge of gonadotropins. The observation that the estradiol-induced gonadotropin surge in ovariectomized rats is of lesser magnitude and duration than that found in the cycling rat at proestrus has resulted in a search for other steroid regulators. Progesterone is a major regulator of the preovulatory gonadotropin surge. It can only act in the presence of an estrogen background, which is necessary for the synthesis of progesterone receptors. In the estrogen-primed ovariectomized rat, progesterone is able to initiate and enhance the gonadotropin surge to the magnitude observed on the day of proestrus and limit it to 1 day. The physiological role of progresterone in the induction of the preovulatory gonadotropin surge has been demonstrated by the attenuation of the progesterone-induced surge and the endogenous proestrus surge by progesterone receptor antagonist RU486 and the progesterone synthesis inhibitor trilostane. The promoter region of the follicle-stimulating hormone (FHS)-beta gene contains multiple progesterone response elements and progesterone brings about FSH release as well. The reduction of progesterone in the 5 alpha-position appears to be important for the regulation of progesterone secretion. Corticosteroids appear to play a significant role in the secondary FSH surge on late proestrus and early estrus.

Aromatization and hydrolysis of norethisterone-3-oxime in rabbit

Two pharmacologically active metabolites, norethisterone (NET) and ethinylestradiol (EE2), were detected by HPLC and HPLC-RIA methods in rabbit plasma following single i.v. and i.g. administration at a dose of 1 mg/20 microCi/kg of [3H]norethisterone-3-oxime (NETO). Approximately 48% (i.v. injection) and 91% (i.g. administration) of the NETO dose were hydrolyzed to NET. Although only 0.35% of the NETO dose was aromatized to EE2, due to its high estrogenic potency, EE2 might contribute to the overall pharmacological pattern of NETO in the rabbit.

High-dose gestagens modulate bone resorption and formation and enhance estrogen-induced endosteal bone formation in the ovariectomized mouse

To determine if gestagens of two separate classes have differing skeletal actions, we studied the effects of pharmacologic doses of norethisterone acetate (NETA), a 19-nortestosterone, and megestrol acetate (MA), a 17 alpha-hydroxyprogesterone, on bone formation and resorption in intact and in ovariectomized mice. In the same set of experiments, we also attempted to determine if these gestagens can alter the skeletal activity of 17 beta-estradiol (E2). Experimentally, the skeletons of 78 female BALB/c mice were prelabeled with [3H]tetracycline (3H-T). The animals were randomized to 13 groups of 6 mice each 3 days after the final 3H-T injection. Ovariectomies (OVX) were performed on 8 groups and sham operations (SO) on 5 groups. To study the skeletal effects of the gestagens, 4 groups each of the OVX and SO mice were treated with controlled-release pellet implants calculated to deliver 80 or 250 micrograms of NETA or MA per day. To study gestagen interactions with E2, 3 groups of OVX mice were treated with either 40 micrograms/day of E2 or 40 micrograms/day of E2 plus 250 micrograms/day of NETA or MA. One group of OVX and one group of SO animals received placebo pellets. Fluorochrome labels were administered 10 and 11 and 3 and 4 days before sacrifice to allow histomorphometric evaluation of bone formation. At the end of the 60 day protocol, tibiae and thoracic vertebrae were removed and processed for quantitating the levels of bone resorption based on the amounts of 3H-T retained in the bones. The femora were fixed and embedded for comparison of diaphyseal bone histomorphometry, and the humeri and lumbar vertebrae were prepared for bone density determinations. Reflecting an increase in bone resorption, 3H-T levels in tibiae and vertebrae were decreased in placebo-treated OVX animals compared to the placebo-treated SO group (p < 0.01). Treatment of both SO and OVX mice with NETA decreased bone resorption in a dose-dependent manner, but MA had no significant effects on vertebral bone resorption and increased bone resorption in the tibiae (p < 0.01). E2 treatment of OVX mice reduced bone resorption, but there were no significant interactions between the E2 and gestagen treatments on resorptive activity. Based on bone histomorphometry of in vivo fluorochrome labels, both gestagens increased periosteal bone formation rates but had no effect on endosteal bone formation (BFRe). In contrast, E2 treatment of the OVX mice stimulated bone formation at the endosteal surface.(ABSTRACT TRUNCATED AT 400 WORDS)

Pharmacokinetics, hydrolysis and aromatisation of norethisterone-3-oxime in female cynomolgus monkey

Norethisterone-3-oxime (NETO) was administered to 3 female cynomolgus monkeys intragastrically and, after a wash-out period of 2-5 weeks, intravenously at a dose of 1 mg/kg. The radioactive dose of tritiated NETO was 20 microCi/kg for both treatments. For i.v. injection, a 30% propylene glycol/water solution and for i.g. administration an aqueous microcrystalline suspension was used. Excretion of radiolabel in urine and feces was followed for 5 days and plasma samples were obtained up to 2 days after administrations. In all samples (urine, feces and plasma) radioactivity was determined. Extracts from plasma samples were subjected to HPLC separation of drug and metabolites, as well as NETO and NET (metabolite of NETO after hydrolysis of the oxime group) levels were determined. In addition, EE2 (ethinylestradiol, A-ring aromatised metabolite of NET) levels were estimated using a specifically designed HPLC system for separation. Quantification of EE2 was achieved by radioimmunoassay (RIA) of specific eluate fractions. The results demonstrate that [3H]-NETO was absorbed completely at a dose level of 1 mg/kg, and excreted predominantly via the kidneys. A urinary to fecal excretion ratio of 1.5 (i.v.) or 1.0 (i.g.) was found. Renal excretion of total radiolabel proceeded with a half-life of about 0.8 (i.v.) or 1.1 (i.g.) days. Balances were incomplete, probably due to technical reasons. Orally administered NETO was highly bioavailable (84.0 +/- 16.9% of dose) but rapidly cleared from plasma (total clearance corresponded to 97% of plasma liver flow). The clearance from plasma is equivalent to the metabolic clearance because almost no unchanged NETO is excreted. Extensive metabolism of the parent drug was observed leading to at least two pharmacologically active metabolites (NET, EE2). The main progestogenic metabolite was NET reaching similar high plasma levels as NETO. EE2 turned out to be a metabolite of NETO and a conversion rate of below 0.5% of dose was estimated. However, due to its high estrogenic potency EE2 might contribute to the overall pharmacological pattern of NETO in the cynomolgus monkey.

Interaction between ovarian and adrenal steroids in the regulation of gonadotropin secretion

Recent work from our laboratory suggests that a complex interaction exists between ovarian and adrenal steroids in the regulation of preovulatory gonadotropin secretion. Ovarian estradiol serves to set the neutral trigger for the preovulatory gonadotropin surge, while progesterone from both the adrenal and the ovary serves to (1) initiate, (2) synchronize, (3) potentiate and (4) limit the preovulatory LH surge to a single day. Administration of RU486 or the progesterone synthesis inhibitor, trilostane, on proestrous morning attenuated the preovulatory LH surge. Adrenal progesterone appears to play a role in potentiating the LH surge since RU486 still effectively decreased the LH surge even in animals ovariectomized at 0800 h on proestrus. The administration of ACTH to estrogen-primed ovariectomized (ovx) immature rats caused a LH and FSH surge 6 h later, demonstrating that upon proper stimulation, the adrenal can induce gonadotropin surges. The effect was specific for ACTH, required estrogen priming, and was blocked by adrenalectomy or RU486, but not by ovariectomy. Certain corticosteroids, most notably deoxycorticosterone and triamcinolone acetonide, were found to possess "progestin-like" activity in the induction of LH and FSH surges in estrogen-primed ovx rats. In contrast, corticosterone and dexamethasone caused a preferential release of FSH, but not LH. Progesterone-induced surges of LH and FSH appear to require an intact N-methyl-D-aspartate (NMDA) neurotransmission line, since administration of the NMDA receptor antagonist, MK801, blocked the ability of progesterone to induce LH and FSH surges. Similarly, NMDA neurotransmission appears to be a critical component in the expression of the preovulatory gonadotropin surge since administration of MK801 during the critical period significantly diminished the LH and PRL surge in the cycling adult rat. FSH levels were lowered by MK801 treatment, but the effect was not statistically significant. The progesterone-induced gonadotropin surge appears to also involve mediation through NPY and catecholamine systems. Immediately preceding the onset of the LH and FSH surge in progesterone-treated estrogen-primed ovx. rats, there was a significant elevation of MBH and POA GnRH and NPY levels, which was followed by a significant fall at the onset of the LH surge. The effect of progesterone on inducing LH and FSH surges also appears to involve alpha 1 and alpha 2 adrenergic neuron activation since prazosin and yohimbine (alpha 1 and 2 blockers, respectively) but not propranolol (a beta-blocker) abolished the ability of progesterone to induce LH and FSH surges. Progesterone also caused a dose-dependent decrease in occupied nuclear estradiol receptors in the pituitary.(ABSTRACT TRUNCATED AT 400 WORDS)

Metabolism of levonorgestrel, norethindrone, and structurally related contraceptive steroids

There is limited information on the metabolism of levonorgestrel, norethindrone and structurally related contraceptive steroids. Both levonorgestrel and norethindrone undergo extensive reduction of the alpha, beta-unsaturated ketone in ring A. Levonorgestrel also undergoes hydroxylation at carbons 2 and 16. The metabolites of both compounds circulate predominantly as sulfates. In urine, levonorgestrel metabolites are found primarily in the glucuronide form, whereas norethindrone metabolites are present in approximately equal amounts as sulfates and glucuronides. Of the progestogens structurally related to norethindrone, norethindrone acetate, ethynodiol diacetate, norethindrone enanthate, and perhaps lynestrenol, undergo rapid hydrolysis and are converted to the parent compound and its metabolites. There is no convincing evidence that norethynodrel is converted to norethindrone. Of the progestogens structurally related to levonorgestrel, it appears that neither desogestrel nor gestodene are transformed to the parent compound. However, there is evidence that norgestimate can be, at least partly, converted to levonorgestrel. Further studies on the metabolism of these progestogens are required before we can understand their mechanism of action.

Integration of the effects of estradiol and progesterone in the modulation of gonadotropin secretion

Estradiol secreted by the maturing follicle is the primary trigger for the surge of gonadotropins leading to ovulation. Progesterone has stimulatory or inhibitory actions on this estrogen-induced gonadotropin surge depending upon the time and dose of administration. The administration of progesterone to immature ovariectomized rats primed with a low dose of estradiol induced a well-defined LH surge and prolonged FSH release, a pattern similar to the proestrus surge of gonadotropins. A physiological role of progesterone is indicated in the normal ovulatory process because a single injection of the progesterone antagonist RU 486 on the day of proestrus in the adult cycling rat and on the day of the gonadotropin surge in the pregnant mare's serum gonadotropin stimulated immature rat resulted in an attenuated gonadotropin surge and reduced the number of ova per ovulating rat. Progesterone administration brought about a rapid LHRH release and an decrease in nuclear accumulation of estrogen receptors in the anterior pituitary but not the hypothalamus. The progesterone effect was demonstrated in vitro in the uterus and anterior pituitary and appears to be confined to occupied estradiol nuclear receptors. In in vivo experiments the progesterone effect on estradiol nuclear receptors appeared to be of approximately 2-h duration, which coincided with the time period of progesterone nuclear receptor accumulation after a single injection of progesterone. During the period of progesterone effects on nuclear estrogen receptors, the ability of estrogens to induce progesterone receptors was impaired. Based on the above results, a model is proposed for the stimulatory and inhibitory effects of progesterone on gonadotropin secretion.

Selective modulation of FSH and LH secretion by steroids

Significant divergence between the pattern of FSH and LH secretion has been observed in the ovulatory cycle, after ovariectomy and during puberty. The presence of an FSH-releasing factor, gonadal FSH inhibiting and releasing peptides and changes in the pulsatile pattern of LHRH secretion are among the postulates used to explain the divergent secretion of FSH and LH. Experiments in our laboratory have shown considerable evidence of differential regulation of FSH and LH secretion by steroids in the absence of gonadal regulatory peptides. Natural and synthetic estrogens show significant differences in the suppression of FSH and LH in the ovariectomized rat using a standard uterine response to the estrogen as the end point. In the immature ovariectomized rat treated with a low dose of estradiol that is sufficient for the synthesis of progesterone receptors to ensure progesterone sensitivity, but not large enough to induce estrogen triggered LH surges, progesterone administration resulted in a pattern of LH and FSH secretion similar to that observed on the day of proestrus in the cycling rat. Selective secretion of FSH was induced in the estrogen primed immature rat model by the administration of progesterone metabolite 5 alpha-dihydroporgesterone (5 alpha-DHP) while selective LH secretion was induced by 3 alpha, 5 alpha-tetrahydroprogesterone (3 alpha,5 alpha-THP). The selective secretion of FSH and LH induced by progesterone metabolites was confirmed in the immature female rat primed with PMSG and maintained in constant light. 5 alpha-DHP was also able to induce a greater release of FSH when administered to the adult cycling rat on proestrus. The priming of the pituitary gonadotrope in secreting a high baseline level of FSH or responding to LHRH in releasing a greater amount of FSH appeared to be an important factor in selective FSH release and such priming can be brought about by 5 alpha-DHP in the absence of gonadal regulatory peptides.

The dynamic interaction between steroids and gonadotropins in the mammalian ovulatory cycle

The interrelationship between steroid hormone secretion and gonadotropin secretion during the human menstrual cycle is a set of complex interactions. The temporal relationship between estradiol and progesterone secretion, the preovulatory surge of gonadotropins and the time of ovulation, has been studied extensively. The median time interval between the first rise of estradiol, progesterone, LH and FSH, and ovulation has been estimated to be 82.5 hr, 7.8 hr, 32 hr and 21.1 hr, respectively. The median time interval between peak blood concentrations of estradiol, LH and FSH, and the time of ovulation is estimated to be 24, 16.5 and 15.3 hr. There is considerable individual variation in the above mentioned estimates. The rising levels of blood estradiol that are secreted by the maturing ovarian follicles appear to be the primary trigger for the surge of gonadotropins leading to ovulation. In the experimental animal, the estrogen effect takes place at the level of the hypothalamus in the release of LHRH and at the level of the pituitary in increasing its sensitivity to LHRH. There appears to be a good correlation between the nuclear translocation of occupied estrogen receptors in the hypothalamus and the pituitary and the manifestation of estrogen effects. In the human, a rise in progesterone begins to take place after the first rise in LH has occurred. Progesterone appears to have both a stimulatory and inhibitory effect on gonadotropin secretion in the experimental animal and the human. Thus it exerts a fine-tune modulatory influence of estrogen effects which include enhancement of the estradiol induced gonadotropin surge, and perhaps the initiation of the midcycle FSH surge in the human. The abrupt termination of the preovulatory gonadotropin surge is difficult to explain because the pituitary gland is not depleted of its gonadotropin content or its capacity to secrete gonadotropins. Preliminary results suggests that progesterone by exerting its inhibitory influence may be responsible for the termination of the gonadotropin surge. This hypothesis, however, needs careful confirmation. The effects of progesterone may be manifested at higher brain centers, the hypothalamus and the pituitary, and may involve not only the release of LHRH but also an alteration of the pulsatile pattern of release of LHRH. The recognition of these components, along with the presence and control of LHRH degrading enzymes in the hypothalamus and the pituitary, emphasize the complexity of the system and the need for further work to gain a better understanding of the steroidal regulation of gonadotropin secretion.

Stimulation of 17 beta-hydroxy steroid dehydrogenase in the rat anterior pituitary gland by progesterone

Anterior pituitary gland and hypothalamic 17 beta-hydroxysteroid dehydrogenase (17 beta-HSD) activity was measured in the immature castrated estradiol primed rat to determine if differences in enzyme activity could explain the progesterone induced reduction of bound estradiol nuclear receptors of the anterior pituitary gland but not the hypothalamus. Higher levels of 17 beta-HSD activity were found in the anterior pituitary gland as compared to the hypothalamus. The enzyme activity in the anterior pituitary gland was stimulated by progesterone administered either in combination with estradiol for 4 days or as a single injection following 4 days of estradiol priming. No progesterone effects were found on hypothalamic 17 beta-HSD. Under the experimental conditions used, progesterone administration did not alter uterine 17 beta-HSD. An increase in anterior pituitary gland and uterine 17 beta-HSD was also induced by estrogen administration.

Oestrogen and testosterone effects on hormone secretion and cell morphology of human pituitary tumours

Estradurin (a polymer of 17-beta-oestradiol) has an inhibitory effect on the synthesis/secretion of PRL. This effect is assumed to be caused by the strong inhibitory effect of the drug on phosphatases. With increasing time of low doses of Estradurin (0.001 micrograms/ml) in vitro, the inhibitory effect on PRL secretion was overcome and the synthesis/secretion of PRL increased. The secretion of GH was unaffected in all concentrations (0.001-0.1 micrograms/ml) except 1 microgram/ml. A stimulatory effect of 17-beta-oestradiol (0.01 micrograms/ml) on the synthesis/secretion of PRL was suggested by the tissue from one post-pregnancy pituitary. Short time organ cultures from prolactinomas or tumors with a concomitant secretion of GH and PRL show no changes of GH or PRL secretion following incubation with (0.001-0.1 micrograms/ml) of 17-beta-oestradiol. However, electron microscopy of 17-beta-oestradiol incubated specimens revealed an increased number of lysosomes and inclusion bodies in the cell cytoplasm. Incubation with testosterone (0.001-1 microgram/ml) cause inhibition of PRL synthesis/secretion in two of three prolactinomas. In GH secreting tumours testosterone did not effect PRL or GH secretion in vitro when compared with controls. The ultrastructural analysis of specimens in which a decrease of PRL synthesis/secretion had occurred showed myelin figures in the cell cytoplasm and accumulations of amorphous electron dense inclusion bodies.

Comparative effects of progesterone, norgestrel, norethisterone and tamoxifen on the abnormal uterus of the anovulatory rat

Progesterone therapy results in partial reversibility of histological abnormalities of the rat uterus exposed to constant oestrogen stimulation and is associated with a decrease in nuclear oestrogen receptor content, which may underlie the tissue response to hormone treatment [White, Moore, Elder & Lim (1982) Biochem. J. 202, 535-41]. The synthetic progestins norgestrel and norethisterone used in this study were as effective as progesterone in decreasing the content of nuclear oestrogen receptor. However, only norgestrel had an ameliorative effect on epithelial hyperplasia and metaplasia. The non-steroidal anti-oestrogen tamoxifen caused a significant decrease in both nuclear and cytosol oestrogen receptor content without any change in luminal epithelial hyperplasia and metaplasia. Each progestin caused an increase, whereas tamoxifen caused a decrease, in the proportion of nuclear oestrogen receptors that were unoccupied. Each compound caused a decrease in the content of cytosol progesterone receptor. The effectiveness of compounds used as oestrogen antagonists is discussed with reference to their mode of action.