Inhibitory Effect Of Estradiol Research Articles

Estradiol acts as a competitive inhibitor of the 3 beta-hydroxysteroid dehydrogenase/delta 5-delta 4 isomerase enzyme of cultured Leydig tumor cells.

To study the local regulatory mechanisms involving steroid hormones in steroidogenic cells, the effect of estradiol on steroidogenesis was investigated using MA-10 Leydig tumor cells. Estradiol inhibited progesterone biosynthesis in MA-10 cells in a dose-dependent manner. Inhibition of progesterone biosynthesis by estradiol was associated with a concomitant accumulation of pregnenolone in the incubation medium. Estradiol inhibited the activity of 3 beta-hydroxysteroid dehydrogenase/delta 5-delta 4 isomerase by a chemical mechanism which is not mediated through the cellular estrogen receptor. Thus, the estrogen receptor agonist diethylstilbestrol did not inhibit this enzyme activity, nor could this agent block the effect of estradiol on the enzyme. Furthermore, estradiol inhibited enzyme activity in isolated microsomes which do not contain estradiol receptor protein. Kinetic analysis of the inhibitory effect of estradiol on 3 beta-hydroxysteroid dehydrogenase/delta 5-delta 4 isomerase revealed that this steroid hormone functions as a competitive inhibitor of the enzyme, with an average apparent Ki of 1.8 microM.

Bipotential Actions of Estrogen on Progesterone Biosynthesis by Ovarian Cells. I. Relation of Estradiol's Inhibitory Actions to Cholesterol and Progestin Metabolism in Cultured Swine Granulosa Cells*

In short term, serum-free cultures of granulosa cells, estradiol inhibited basal progesterone production by more than 84% in a time- and dose-dependent fashion. Half-maximal inhibition (ID50) was observed at a mean estradiol concentration of 70 ng/ml. The acute inhibitory effects of estradiol were independent of cell density or maturational status of the parent follicle (small, medium, or large follicles). Estrogen decreased total progesterone biosynthesis, rather than merely progesterone secretion by granulosa cells. In addition, the production of progesterone and its 20 alpha-reduced metabolite were suppressed in parallel over a 30-fold range of inhibitory effects. Moreover, estradiol inhibited progesterone production from both endogenous and exogenous (25-hydroxycholesterol) substrate. In contrast to its inhibition of progesterone production, estradiol acutely enhanced pregnenolone accumulation and led to a 14- to 20-fold increase in the ratio of pregnenolone to progesterone. Inhibition of 3 beta-hydroxysteroid dehydrogenase activity was confirmed by demonstrating estrogen's ability to antagonize the conversion of exogenously supplied pregnenolone to progesterone in intact granulosa cells (ID50, 74 ng/ml) and to directly inhibit enzymic activity in ovarian homogenates (ID50, 79 ng/ml). On the other hand, estradiol did not alter the incorporation of [14C]acetate into cholesterol and specific progestins or influence the time-dependent hydrolysis of prelabeled cholesteryl ester stores in granulosa cells. In summary, in short term cultures of swine granulosa cells, estradiol significantly inhibits basal progesterone biosynthesis in a time- and dose-dependent fashion, encompassing estradiol concentrations attainable in vivo. Estrogen's inhibition is accomplished by mechanisms that are independent of cytotoxicity, cell density, and maturational stage of the parent follicle. The predominant locus of estrogen action is blockade of pregnenolone's conversion to progesterone, rather than accelerated metabolism of progesterone to its 20 alpha-reduced metabolite. Moreover, estradiol simultaneously enhances functional cholesterol side-chain cleavage activity without suppressing de novo cholesterol biosynthesis or impairing the mobilization of cellular cholesteryl ester stores. Thus, we infer that increasing concentrations of estradiol attained in antral follicular fluid during the later stages of follicle maturation could effectively limit the premature secretion of large quantities of progesterone before ovulation without impairing the cell's capacity for de novo cholesterol biosynthesis or cholesteryl ester hydrolysis.

A biphasic effect of estradiol on serotonin metabolism in rat pineal organ cultures.

Physiological amounts of estradiol (1 nM) significantly increased serotonin, conversion to melatonin and 5-methoxytryptophol by rat pineal glands in organ culture whereas larger, pharmacological, doses (i.e. 1000 nM) impaired it significantly. The stimulatory but not the inhibitory effect of estradiol was blocked by the simultaneous addition of puromycin in the culture medium.

Possible role of prolactin in the inhibitory effect of estradiol on the hypothalamic-pituitary-testicular axis in the rat.

Acute estradiol benzoate (EB) administration to intact adult male rats reduced basal and hCG-stimulated plasma testosterone (T) levels and decreased basal and LHRH-stimulated LH levels. Long term EB administration had similar effects on T levels. Basal LH levels were more markedly depressed than during short term administration, but the response to LHRH stimulation was increased. PRL levels were significantly elevated during both short and long term EB treatment. Hyperprolactinemia induced by grafting two pituitaries of littermate donors under the kidney capsule of a male adult intact rat was associated with reduced basal and LHRH-stimulated LH levels and reduced T responses to hCG. The administration of bromocriptine to EB-treated rats prevented the increase in serum PRL in response to estrogen and restored normal LH responses to LHRH and T responses to hCG. This suggests that PRL may play an intermediary role in the inhibitory effect of estrogens on pituitary-testicular function.

OESTROGEN INDUCED LEYDIG CELL REFRACTORINESS TO GONADOTROPHIN STIMULATION

ABSTRACT In vivo administration of oestradiol to male rats modifies plasma LH, FSH and testosterone levels, cAMP and testosterone production and DNA synthesis in isolated interstitial cells. Intramuscular injection of oestradiol benzoate (Oe2B) at the dose of 1 or 100 μg/day for 6 days induced a 5- and 10-fold decrease in plasma testosterone, respectively, and a 2-fold decrease in plasma LH and FSH. Plasma testosterone was already significantly decreased 2 h after the Oe2B injection at which point the plasma LH and FSH levels were not yet significantly decreased. In vivo steroidogenic responsiveness to hCG evaluated by plasma and testicular contents was already significantly lower than that of controls 2 h following oestradiol administration. Thereafter response to hCG progressively decreased during the 6 days of 1 or 100 μg oestradiol treatment, reaching 30 and 10 %, respectively, of that of controls on the last day. On the contrary the testicular cAMP content 2 h after hCG injection was significantly higher in oestradiol treated animals than in controls after 24 h. The number of hCG binding sites in isolated Leydig cells decreased to approximately 50 % of that of controls on days 3 to 6 following Oe2B treatment. In vitro testosterone production by isolated interstitial cells, either under basal conditions or under stimulation by hCG or N6O2 dibutyryl adenosine 3′,5′-monophosphate (DbcAMP), was lowered as early as 2 h following the injection of Oe2B to the animals. From 1 to 6 days following Oe2B administration, testosterone secretion, in response to both stimuli, was approximately 4 times lower than that of the control animals. Paradoxically, by the second day of oestrogen treatment, basal and hCG induced in vitro cAMP production by interstitial cells was significantly higher than controls despite a significant decrease in the number of binding sites. The incorporation of thymidine into interstitial cells DNA were decreased following 2 days of oestrogen administration. However, the conversion of pregnenolone to testosterone was unchanged. These inhibitory effects of oestradiol were not overcome by simultaneous administration of hCG. These results strongly suggest that the rapid inhibitory action of oestradiol on interstitial cell function, steroidogenesis, and DNA synthesis, occurs at the testicular level. Changes observed in gonadotrophin receptor sites or in plasma LH levels may have a long term effect on the steroidogenic refractoriness to hCG. However this refractoriness is primarily related to an abnormality of some step of steroidogenesis beyond cAMP formation.

Effects of Estradiol and Prolactin on Growth of Rat Mammary Adenocarcinoma Cells in Monolayer Cultures

The effects of estradiol and ovine prolactin on the growth of a rat mammary adenocarcinoma cell line were investigated. The action of estradiol was dose-dependent. At less than or equal to 1 mug/ml it did not influence growth, at 5-10 mug/ml it was inhibitory, and at 20 mug/ml it was toxic. Prolactin alone had little effect on growth. However, the inhibitory effect of estradiol could be counteracted by a high concentration of prolactin. It appears, therefore, that the growth of cultured rat mammary adenocarcinoma cells can be regulated by the ratio of prolactin to estradiol: When the ratio is high growth is favored; when it is low, growth is inhibited.

Effect of ovariectomy on oestrogen-sensitive feedback elements.

Serum LH and FSH were determined by radioimmunoassay in untreated and oestrogen-treated ovariectomized rats. The animals were sacrificed 7, 14, 21 and 28 days after ovariectomy. Oestradiol benzoate was administered in the daily dose of 50 mug on the 2 days preceeding sacrifice. It has been found that oestrogens exert a strong inhibitory effect on the release of LH, as evidenced by a decrease in serum titers of the hormone. Oestradiol suppressed LH almost completely in animals with both low (7 or 14 days post-ovariectomy), and high levels of serum LH(21 or 28 days post-ovariectomy). Oestradiol failed to totally suppress serum FSH at any post-castration time considered. Moreover, the inhibitory effect of oestradiol on FSH release decreased as post-castration time increased. These data suggest that the feedback mechanisms which control the secretion of LH and those which control the secretion of FSH are substantially different.

Changes in sensitivity of the estradiol-LH feedback system with puberty in the female rat.

The question of a decrease in sensitivity to the inhibitory effects of estradiol (E2) on LH release in relation to puberty was re-examined. The rats were fitted with indwelling venous catheters making it possible to monitor plasma LH levels by radioimmunoassay longitudinally in individual animals and to administer E2 as a virtually continuous infusion. The rats were ovx at 19 (prepuberal) or 45–55 days of age (postpuberal), and one week later a polyethylene catheter was introduced into the vena cava via the right external jugular vein and an infusion of E2 or saline started (rate = 1.14 ml/24 hr.). The infusion was interrupted daily between 1600–1800 hr (time of preovulatory LH surge of intact adults) for 10 min for blood collection. In control pre and postpuberal rats infused with saline plasma LH levels exceeded 160 ng/ml (LER 1213A) one week after ovx. In rats ovx after puberty LH was not suppressed by infusion of 0.32 µg E2/100 g/day, while in the spayed prepuberal rats, plasma LH was lowered by a qua...

In vitrosusceptibility ofCryptococcus neoformansto steroids

The inhibitory effect of estradiol, norethynodrel, progesterone, testosterone and diethylstilbestrol on 7 human isolates of C. neoformans was determined. Northynodrel, progesterone or testosterone had no apparent effect on their growth. Diethylstilhestrol at a concentration of 10 μg/ml completely suppressed the growth of all isolates and estradiol at a concentration of 1·0 μg/ml completely suppressed the growth of 3 isolates and moderately inhibited the remainder.

Mammalian cell fusion. IV. Regulation of chromosome formation from interphase nuclei by various chemical compounds.

AbstractHybrid HeLa cells formed by the fusion of mitotic with interphase cells have been used as a test system to study the effects of various positively and negatively charged compounds on the induction of premature chromosome condensation (PCC) of the interphase nuclei. Among the various positively charged compounds tested, spermine, putrescine and Mg++ were specific in promoting the PCC induction while spermidine was unique in inhibiting this event. All the negatively charged compounds including estradiol‐17β were uniformly inhibitory. The inhibitory effect of estradiol was reversed by putrescine. The inhibition of PCC induction by estradiol seems to be due to its binding to interphase chromatin rather than to the PCC inducers. The differences between the polyamines in their effects on the PCC inducing system has been explained on the basis of their abilities to bind stereospecifically with chromatin.

Quantitative studies of hair growth in the albino rat. III. The role of the adrenal glands.

SUMMARY 1. Adrenalectomy 2 weeks before the start of the second wave of hair growth advanced the beginning of the wave in female rats, and speeded its passage over the body in both males and females. The rate of loss of club hairs was slightly accelerated, but there was no effect on the definitive length of hair produced. 2. Adrenalectomy after the wave of hair growth had begun was less effective. 3. ACTH did not affect the time at which the wave of hair growth began but delayed its passage. ACTH had no effect on the loss of club hairs nor on the definitive length of hair produced. 4. Implantation of oestradiol retarded the start and rate of passage of the wave, and the loss of club hairs in both spayed and spayed adrenalectomized animals. Oestradiol must therefore have some action which is independent of the adrenals. Nevertheless, inhibitory effects of oestradiol on these aspects of hair growth were enhanced by the presence of the adrenals. The action of oestradiol in reducing the rate of hair growth was, on the other hand, unaffected by the presence or absence of the adrenals. 5. Adrenal hormones delay the passage of the growth wave to a greater extent than ovarian hormones, but they have no effect on the rate of hair growth, and, compared with ovarian hormones, affect the loss of club hairs only slightly. It is therefore suggested that these three main phases of hair growth may be controlled by mechanisms which are at least partially independent.