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J Simard

Publications and source records attributed to J Simard.

At least 73 records · Page 4Linked to original sources
PubMed1989

Inhibitory effect of estrogens on GCDFP-15 mRNA levels and secretion in ZR-75-1 human breast cancer cells.

In order to better understand the mechanisms responsible for the antagonism between steroids in human breast cancer cells, we have studied the effect of 17 beta-estradiol (E2), dihydrotestosterone (DHT), and dexamethasone (DEX) alone or in combination on the expression of the breast gross cystic disease fluid protein-15 (GCDFP-15) in ZR-75-1 cells. Incubation with E2 markedly decreased basal GCDFP-15 mRNA levels accompanied by a parallel inhibition of the secretion of this tumor marker, the estrogenic effect being exerted at a half-maximal concentration of about 44 pM E2. The inhibitory effect of E2 on GCDFP-15 expression was competitively reversed by the antiestrogen LY156758. In addition, 1 nM E2 inhibited the marked stimulation induced by 1 nM DHT or 300 nM DEX on GCDFP-15 mRNA accumulation and on the secretion of the glycoprotein. However, at the concentration used, E2 reversed by only 65% the stimulation achieved by the combination of DHT and DEX on GCDFP-15 mRNA levels. It is of interest to mention that the effect of DHT, DEX, and E2 on GCDFP-15 expression is opposite to the respective effect of each steroid on ZR-75-1 cell proliferation. The present data on the regulation of GCDFP-15 mRNA demonstrate an estrogen-induced inhibition of mRNA levels under physiological conditions, thus offering a unique opportunity to study the mechanisms involved in the down-regulation of gene expression by estrogens and to achieve a better understanding of the antagonism between estrogens, androgens, glucocorticoids, and progestins in breast cancer cells. Furthermore, GCDFP-15 could well be a good marker for monitoring the response to androgens and antiestrogens during the course of breast cancer therapy.

Apolipoproteins↗
PubMed1989

Characterization of cDNAs for human estradiol 17 beta-dehydrogenase and assignment of the gene to chromosome 17: evidence of two mRNA species with distinct 5'-termini in human placenta.

Human placenta estradiol 17 beta-dehydrogenase (E2DH) cDNA clones were isolated from a lambda gt11 expression library by screening with 33 mer synthetic oligonucleotides derived from the amino acid sequence of the catalytic site of E2DH and with polyclonal antibodies raised against the enzyme purified from human placenta. Using 32P-labeled fragments from the coding and 5'-untranslated regions, two mRNA species have been identified in poly(A)+ RNA from human placenta, a major species migrating at 1.3 kilobases (kb) while a minor one is found at 2.2 kb. Primer extension analysis identifies the major mRNA as starting 9-10 nucleotides upstream from the in-frame ATG initiating codon while the longer mRNA has at least 814 noncoding nucleotides at its 5'-terminus. Sequence analysis of the longest cDNA clone (2092 base pairs) shows that this clone possesses identical coding and noncoding sequences in the regions of overlap with the shorter cDNA clones. The 32P-labeled 5'-noncoding fragment hybridized only to the 2.2 kb band, thus providing additional evidence for the existence of two distinct mRNA species which differ only in their 5'-noncoding regions. Using hpE2DH36 cDNA as a probe for in situ hybridization, the human E2DH gene was localized to the q11-q12 region of chromosome 17. The cloned cDNAs encode E2DH, a 327-amino acid protein having a calculated molecular weight of 34,853. Since E2DH is the enzyme required for the formation of 17 beta-estradiol, the availability of the cDNA encoding the enzyme should permit a detailed investigation of the factors regulating the expression and activity of this crucial enzyme, in both normal and malignant tissues, especially breast cancer.

17-Hydroxysteroid Dehydrogenases↗
PubMed1988

Full oestrogenic activity of C19-delta 5 adrenal steroids in rat pituitary lactotrophs and somatotrophs.

Oestrogens are known to exert specific stimulatory effects on basal and dopamine (DA)-inhibited prolactin (PRL) release as well as on PRL cell content in rat adenohypophysial cells in primary culture. Recently, we have demonstrated that classical oestrogens increase growth hormone (GH) release and cellular GH content in rat pituitary somatotrophs. Since there is evidence that 5-androstene-3 beta, 17 beta-diol (delta 5-diol), a metabolite of dehydroepiandrosterone (DHEA) and DHEA-sulfate (DHEA-S) can induce typical oestrogenic responses in target tissues, we have investigated the effect of C19 adrenal steroids and compared them to that of 17 beta-oestradiol (E2) on the above-indicated parameters. Following a 72-h incubation, maximal concentrations of E2, delta 5-diol and DHEA caused a similar increase in PRL cell content at respective EC50 values of 0.020, 14 and 115 nM. The sensitivity of lactotrophs to DA action was decreased by approximately 4-fold after a 48-h exposure to maximal concentrations of delta 5-diol or DHEA. The time course of the antidopaminergic effect of delta 5-diol and DHEA was almost superimposable to that of E2. A 72-h incubation with 5 microM DHEA-S, a concentration within the range of blood levels found in women, doubled (P less than or equal to 0.001) cellular PRL accumulation. On the other hand, androstenedione (delta 4-dione) was without effect on any of the parameters measured. All stimulatory effects induced by maximal effective concentrations of delta 5-diol, DHEA or DHEA-S were competitively inhibited by simultaneous incubation with the antioestrogen LY156758. The amplitude of the stimulatory effects of delta 5-diol and DHEA on GH cell content as well as on spontaneous GH-releasing factor (GRF)-induced GH release was superimposable to that observed with E2. The effect of the steroids on GH cell content was exerted at 0.016 nM (E2), 12 nM (delta 5-diol) and 250 nM (DHEA). Simultaneous incubation with LY156758 completely blocked the effect of maximally effective concentrations of E2, delta 5-diol and DHEA in somatotrophs. Furthermore, a physiological concentration of DHEA-S (5 microM) enhanced spontaneous as well as GRF-induced GH release. On the other hand, delta 4-dione as well as testosterone and dihydrotestosterone did not alter GH release. The present data demonstrate that delta 5-diol, DHEA and DHEA-S can exert full oestrogenic effects in lactotrophs and somatotrophs, thus supporting their potential oestrogenic role under both physiological and pathological conditions.

Androgens↗
PubMed1988

Effect of luteinizing hormone releasing hormone (LHRH) and [D-Trp6, des-Gly-NH2(10)]LHRH ethylamide on alpha-subunit and LH beta messenger ribonucleic acid levels in rat anterior pituitary cells in culture.

The effect of incubation with LHRH and its agonist [D-Trp6, des-Gly-NH2(10)]LHRH ethylamide has been measured on the concentrations of mRNAs for the common alpha-subunit of glycoprotein hormones and beta-LH in rat anterior pituitary cells in primary culture. After incubation, total RNA was analyzed by Northern blot or dot blot hybridization with alpha- and LH beta 32P-labeled cRNA probes and mRNA levels were quantified by autoradiography. Short-term treatment (4-6 h) of pituitary cells with 100 nM LHRH led to a marked stimulation of LH release but no effect was observed on alpha-subunit or LH beta mRNA levels. Longer (24-72 h) incubation periods with LHRH led to complete desensitization of the LH response to the neurohormone and induced 2- to 3-fold increases in alpha-mRNA cell content while LH beta mRNA levels remained unchanged. Maximal induction of alpha mRNA accumulation was observed with an LHRH concentration as low as 0.1 nM. Incubation with the LHRH agonist [D-Trp6, des-Gly-NH2(10)]LHRH ethylamide for 24-72 h also increased alpha mRNA but did not modify LH-beta mRNA levels. It is concluded that long-term exposure of anterior pituitary cells to LHRH or to an LHRH agonist positively regulates alpha-subunit gene expression in the absence of change in LH beta mRNA levels. This observation can provide an explanation for the high plasma levels of free alpha-subunits found in patients treated chronically with LHRH agonists.

Animals↗
PubMed1988

Modulation by sex steroids and [D-Trp6, Des-Gly-NH2(10)]luteinizing hormone (LH)-releasing hormone ethylamide of alpha-subunit and LH beta messenger ribonucleic acid levels in the rat anterior pituitary gland.

LHRH and sex steroids play a major and direct regulatory role in the secretion of LH by the anterior pituitary gland. The aim of the present study was to investigate the interactions between sex steroids, more especially the potentiating effect of progesterone (P) in the presence or absence of a low dose of 17 beta-estradiol (E2) and/or dihydrotestosterone (D) on mRNA levels encoding the alpha- and beta-subunits of LH in both female and male rats. We also studied the effect of 2-week treatment with the LHRH agonist [D-Trp6, des-Gly-NH2(10)]LHRH ethylamide on the same parameters. After treatment with the LHRH agonist (5 micrograms daily), the accumulation of mRNA encoding the alpha-subunit was stimulated by approximately 3-fold while the LH beta mRNA concentration remained unchanged. Ovariectomy performed 14 days earlier, increased pituitary alpha and LH beta mRNA levels by 3.7- and 8.8-fold, respectively, while orchiectomy performed 14 days earlier increased alpha and LH beta mRNA levels by 6- and 6.5-fold, respectively. The present data demonstrate that although P alone exerts no effect on alpha and LH beta mRNA levels in castrated animals, treatment with P markedly potentiates the inhibitory effect of E2 on both mRNA levels in female as well as male rats. In addition, P potentiates the inhibitory effect of D on LH beta mRNA levels in castrated female rats. Furthermore, the present study illustrates the importance of the cumulative inhibitory effects of relatively low doses of E2 and D on mRNAs encoding both LH subunits. Moreover, the present observation of a differential modulation of alpha-subunit and LH beta mRNA levels after chronic treatment with an LHRH agonist offers an explanation for the high plasma levels of free alpha-subunit found in patients treated with LHRH agonists.

Animals↗
PubMed1988

Effects of sex steroids on regulation of the levels of C1 peptide of rat prostatic steroid-binding protein mRNA evaluated by in-situ hybridization.

Prostatic steroid-binding protein (PBP) is the most abundant protein synthesized in the rat ventral prostate. The protein is under strict androgenic control and is made of two subunits containing the polypeptides C1, C2 and C3. Using an 35S-labelled cDNA probe, we have used quantitative in-situ hybridization to assess the regulation of polypeptide C1 mRNA levels by sex steroids in the adult male rat. Densitometric quantification of autoradiographic hybridization signals revealed that a significant decrease in C1 mRNA levels could be detected 5 h after castration. Levels of C1 mRNA decreased by 50% 2.5 days after castration, while undetectable levels were reached within 7 days. Administration of the potent androgen 5 alpha-dihydrotestosterone to castrated rats caused a progressive increase in C1 mRNA levels which became significant 5 h after the first injection, while prolonged treatment, for 3 and 7 days, caused 50 and 100% reversals respectively of the effect of castration on C1 mRNA levels. Similar results were obtained by dot-blot hybridization using the same 32P-labelled cDNA probe, thus confirming the specificity and quantification achieved by in-situ hybridization. Administration of oestradiol-17 beta to orchiectomized adult rats for 14 days had no effect on steady-state C1 mRNA levels. Progesterone, on the other hand, at the dose used (2 mg twice daily) caused a marked increase in C1 mRNA levels, measured by in-situ hybridization, which was completely reversed by concomitant administration of the pure antiandrogen flutamide. The present data clearly demonstrate that the expression of PBP C1 peptide mRNA is under strict androgenic control and is a very sensitive and specific parameter of androgenic activity. They also indicate that quantitative in-situ hybridization is a powerful, sensitive and most efficient tool to study the regulation of gene expression while, in addition, providing precise information about the site of mRNA localization as well as information about the histology of the tissue, particularly the heterogeneous nature of the acinar response to androgenic stimulation and deprivation.

Androgen-Binding Protein↗
PubMed1987

Combination therapy in stage C and D prostatic cancer: rationale and five year clinical experience.

In 1941, Huggins and his colleagues discovered that testicular androgens exert a stimulatory effect on prostate cancer growth. Our group has made the key observations that the human adrenals, in addition to the tests, also secrete important amounts of androgens and cancer cells exhibit a marked heterogeneity of androgen sensitivity. In fact, human adrenals secrete large amounts of precursor steroids that are converted into active androgens in peripheral tissues (including the prostate), thus providing 40% to 50% of total androgens in adult men. The action of these androgens remaining after castration can be inhibited in prostatic cancer tissue by administering a pure antiandrogen that also decreases the local concentration of dihydrotestosterone (DHT). The castration levels of serum testosterone left in men after castration have an important stimulatory activity on the growth of androgen-sensitive normal as well as cancer tissues. Cancer cells have markedly different requirements for androgens. Some cell clones can grow in the presence of minimal amounts of androgens, requiring more complete androgen blockade and more potent antiandrogens for inhibiting growth. Among the compounds recommended as antiandrogens, the most unexpected finding is that many of them are devoid of any antiandrogenic activity. In fact, medroxyprogesterone acetate, chlormadinone acetate, and megestrol acetate have androgenic activity, but do not inhibit the peripheral action of DHT in prostatic tissue. These compounds should not be classified as antiandrogens. Cyproterone acetate, on the other hand, is a mixed agonist-antagonist. The only compounds showing pure antiandrogenic activity are Flutamide and its analogues. There is thus a need for a more complete blockade of androgens of both testicular and adrenal origins in order to exert a maximal inhibitory effect on cancer growth. We have therefore performed clinical studies in previously untreated stage D2 and C prostate cancer patients with the combination therapy using the LHRH agonist [D-Trp6, des Gly NH2(10)] LHRH ethylamide and the antiandrogen Flutamide. There was a significant increase in patients with a complete response, as compared with studies limited to the removal or blockade of testicular androgens. There was also a significant decrease in the number of non-responders, an increased duration of positive response, and a decrease in the death rate. This was achieved with minimal or no side effects, thus preserving a good quality of life.

Adrenal Glands↗
PubMed1987

Adrenal C19-5-ene steroids induce full estrogenic responses in rat pituitary gonadotrophs.

Previous studies have shown that the C19 adrenal steroid 5-androstene-3 beta, 17 beta-diol (5-ene-diol), a metabolite of dehydroepiandrosterone (DHEA), can stimulate typical estrogenic responses in target tissues. Since estrogens are known to cause a specific stimulatory effect on LHRH-induced LH release in rat anterior pituitary cells in culture, we have taken advantage of the precision of this system to study the effect of 5-ene-diol or DHEA on this precise estrogen-sensitive parameter. Pretreatment for 48 h with 17 beta-estradiol (E2), 5-ene-diol or DHEA induces a 2.4-, 2.7- and 2.6-fold stimulation of LH release induced by 0.3 nM LHRH, the effect being exerted at respective 50% maximally effective concentrations (ED50 values) of 0.015, 45 and 115 nM. Following a 48-h preincubation with 10 nM E2, 1 microM 5-ene-diol or 1 microM DHEA, the maximal LH and FSH responses to LHRH are increased by approx 50% above control. On the other hand, the sensitivities of the LH and FSH responses to LHRH as assessed by ED50 values of LHRH action are increased by 3.3- to 7.5-fold. As further proof of the estrogenic nature of the effect of 5-ene-diol and DHEA, the effects of E2, 5-ene-diol and DHEA are inhibited competitively by simultaneous incubation with the antiestrogen LY156758 (keoxifene). The 2-fold stimulation of LHRH-induced LH release caused by DHEA-S, at concentrations within the range found in the plasma of women, is also completely blocked by 120 nM LY156758. In direct binding studies, 5-ene-diol and DHEA or DHEA-S have approx 85- and greater than 10,000 lower affinities than E2, respectively, for the estrogen receptor in rat anterior pituitary homogenate and human breast carcinoma cytosol. The present data clearly show that 5-ene-diol, DHEA and DHEA-S can exert full estrogenic activity in rat gonadotrophs, thus supporting the potential estrogenic role of these C19 adrenal steroids in estrogen-dependent processes, especially breast cancer.

Androstenediol↗
PubMed1986

Atrial natriuretic factor-induced cGMP accumulation in rat anterior pituitary cells in culture is not coupled to hormonal secretion.

While atrial natriuretic factor (ANF) does not influence ACTH secretion, it was reported to have a marked stimulatory effect on the intracellular accumulation of cGMP in rat anterior pituitary cells in culture. Since many biological actions of ANF appear coupled to its excitatory action on target cell guanylate cyclase, the current study was designed to characterize the ANF-induced cGMP response in anterior pituitary with a view to determining whether the nucleotide plays a regulatory role in the secretory function of this gland. A 3 min exposure of cells in primary culture to 300 nM ANF (99-126) or 100 microM sodium nitroprusside (SNP), a stimulator of guanylate cyclase, causes maximal 10- and 3-fold elevations of cGMP levels, respectively. Following a progressive decrease, 6- and 2-fold increases over basal cGMP levels are still observed after 180 min of incubation with ANF (99-126) and SNP, respectively. The half-maximal stimulation of cGMP accumulation induced by a 10 min exposure to ANF (99-126), or rat atriopeptin II (ANF 103-125) is observed at 9 +/- 2 and 125 +/- 22 nM, respectively. ANF fragments (99-109) and (111-126), as well as human cardiodilatin (hANF 1-16), do not alter cGMP levels. Basal and ANF-induced cGMP levels are at least 10-fold higher in cell populations enriched in gonadotrophs compared to gonadotroph-impoverished preparations. A 3 h incubation of cells with ANF (0.1-1000 nM), however, fails to modify spontaneous or LHRH-induced LH secretion. Similarly, ANF does not alter spontaneous release of GH, TSH or PRL. The data suggest indirectly that gonadotrophs represent a principal site at which ANF acts to stimulate cGMP synthesis, but that the nucleotide is not a specific regulator of the LH secretory process; nor is it generally involved as a second messenger in the secretory function of any cell type of the anterior pituitary gland.

Animals↗
PubMed1986

Atrial natriuretic factor does not affect basal, forskolin- and CRF-stimulated adenylate cyclase activity, cAMP formation or ACTH secretion, but does stimulate cGMP synthesis in anterior pituitary.

The report that ANF inhibits basal and CRF-stimulated adenylate cyclase activity in anterior pituitary homogenates suggested that the atrial peptide could inhibit ACTH secretion. This possibility was investigated in the ACTH-secreting AtT-20 mouse pituitary tumor cell line as well as homogenates or primary cell cultures from rat anterior hypophysis. ANF (up to 5 X 10(-7) M) was found to be completely ineffective in stimulating basal, CRF- and/or forskolin-stimulated adenylate cyclase activity, cAMP accumulation and ACTH secretion. Similarly, ANF had no effect on spontaneous or GRF-induced GH release from cells in primary culture. ANF receptors, however, are present in AtT-20 cells and anterior pituitary cells as evidenced by the ability of the peptide to stimulate intracellular cGMP accumulation. The data, therefore, suggests that ANF does not have a negative modulatory action on the secretory function of anterior pituitary. The role of cGMP in any other action(s) of ANF remains unknown.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1986

Characteristics of the desensitization of growth hormone and cyclic AMP responses to growth hormone-releasing factor and prostaglandin E2 in rat anterior pituitary cells in culture.

Upon first exposure, synthetic human growth hormone-releasing factor (GRF) and prostaglandin E2 (PGE2) cause a rapid and marked stimulation of cyclic AMP accumulation and GH release in rat adenohypophysial cells in primary culture. However, a marked attenuation of these responses occurs following previous incubation with the 2 compounds. A 50% desensitization of the cyclic AMP and GH responses is observed after 100 and 150 min of preincubation with 300 nM GRF, respectively. After a prior exposure to 3 microM PGE2, a 50% maximal decrease of the cyclic AMP and GH responsiveness to a subsequent 3 h incubation with PGE2 is obtained at 90 and 120 min, respectively. Following preincubation with GRF, a loss of responsiveness of the cyclic AMP and GH responses is also observed after heterologous stimulation with PGE2. A similar heterologous desensitization to the action of GRF is observed following pretreatment with PGE2. The desensitizing action of GRF on the cyclic AMP and GH responses is obtained at respective IC50 values of 2 and 7 nM for both the homologous and heterologous responses. The sensitivity of the desensitizing effect of GRF (7 nM) is thus identical to that of its stimulatory action on GH release (6.2 nM). The desensitization to GRF, in analogy to that to PGE2, is mainly due to a decrease in the maximal action of GRF. Although GH cell content is decreased by previous exposure to GRF and/or PGE2, the ability of forskolin, cholera toxin, 8-bromo 3',5'-adenosine cyclic monophosphate and 3-isobutyl-1-methylxanthine to stimulate GH release remains unchanged in cells pretreated with these compounds, thus indicating that the loss of responsiveness to GRF and PGE2 is not due to a depletion of the releasable pool of GH. On the other hand, nifedipine, a potent calcium channel antagonist, completely abolishes the stimulatory effect of GRF on GH release while not affecting basal and GRF- or PGE2-induced cyclic AMP accumulation. Preincubation with nifedipine has no influence on the desensitizing effect of GRF or PGE2 on either the cyclic AMP or GH responses to the same stimuli. In addition to showing the cross-desensitization by GRF and PGE2, the present results strongly suggest that the desensitization does not result from a depletion of the GH releasable pool but most likely results from a down-regulation and/or an impairment of coupling of a component of the adenylate cyclase system independent from calcium uptake.

1-Methyl-3-isobutylxanthine↗
PubMed1986

Characteristics of interaction of the antiandrogen flutamide with the androgen receptor in various target tissues.

In rat adenohypophysial cells in primary culture, the specific uptake of [3H] testosterone (T) is completely blocked by increasing concentrations of the pure antiandrogen flutamide-OH, the active metabolite of flutamide at an IC50 value of 50 nM while unlabeled T causes a similar inhibition at an IC50 value of 0.5 nM. After 210 min of incubation of 3 nM [3H]T with the anterior pituitary cells, 80% of radioactivity is still present as unchanged T. Direct binding studies show that flutamide-OH and flutamide interact with the rat anterior pituitary androgen receptor at Ki values of 55 and 1275 nM, respectively. In rat ventral prostate (cytosolic and nuclear fractions) and cytosol from human prostatic carcinoma, rat uterus and mouse Shionogi mammary carcinoma, the Ki values ranged from 0.1 to 0.47, 0.6 to 2.7, 62 to 205 and 1450 to 7550 nM for dihydrotestosterone, T, flutamide-OH and flutamide, respectively . Since the ability of flutamide-OH to inhibit the uptake of [3H]T in intact adenohypophysial cells and to compete for binding to the adenohypophysial androgen receptor shows almost identical values at approximately 1% of the potency of T itself, it is most likely that the antiandrogen activity of flutamide-OH can be completely explained by the ability of the pure antiandrogen to displace androgen from their specific receptor in target tissues. In addition, the finding of similar binding characteristics in a series of other tissues suggests that a similar potency of the antiandrogen can be expected in the other androgen-target tissues.

Anilides↗
PubMed1986

Regulation of growth hormone mRNA and pro-opiomelanocortin mRNA levels by cyclic AMP in rat anterior pituitary cells in culture.

To understand the hormonal regulation of steady-state growth hormone (GH) mRNA levels, we investigated the interaction between somatostatin and agents known to increase intracellular cAMP activity on GH mRNA, GH synthesis, cell content of GH, and GH release in primary cultures of rat anterior pituitary cells. We simultaneously studied the modulation of the steady-state of pro-opiomelanocortin (POMC) mRNA levels by cAMP. In four independent experiments, a 48-hr exposure to 0.3 mM 3-isobutyl-1-methylxanthine (IBMX) or 3 mM 8-bromoadenosine 3',5'-cyclic monophosphate (8Br-cAMP) increased GH mRNA levels from 70 to 170% and from 70 to 150% above control (p less than 0.001), respectively. Parallel increases in GH release accompanied by a corresponding decrease in the intracellular content of GH were also obtained. Following a 48-hr incubation with 100 nM somatostatin alone, no change in GH mRNA levels was observed whereas GH release was inhibited by 90%, GH cell content doubled, and GH synthesis decreased by 40%. Surprisingly, somatostatin potentiated the enhancing effect of 8Br-cAMP on GH mRNA levels. In the same cell preparation, a 48-hr exposure to IBMX or 8Br-cAMP stimulated adrenocorticotropin release by 9.4- and 18.0-fold, respectively, and increased POMC mRNA levels by 2.4- and 2.3-fold (p less than 0.001), respectively. No change in beta-actin mRNA was observed after these treatments. These data indicate that increased intracellular cAMP concentrations increase the steady-state level of GH mRNA.(ABSTRACT TRUNCATED AT 250 WORDS)

1-Methyl-3-isobutylxanthine↗
PubMed1986

Stimulation of growth hormone release and synthesis by estrogens in rat anterior pituitary cells in culture.

We have investigated the potential effect of estrogens in the control of GH secretion in rat anterior pituitary cells in primary culture. We have found that a 72-h preincubation with 17 beta-estradiol (E2) caused an approximately 2- to 3-fold stimulation of basal and GH-releasing factor (GRF)-induced GH release as well as cellular GH content at EC50 values of 44, 35, and 15 pM, respectively. Estrone and estriol also increased GH release at respective EC50 values of 100 and 250 pM. The stimulatory effects of these steroids on GH release and cellular GH content were competitively blocked by simultaneous incubation with the antiestrogen LY156758. In contrast to thyroid and glucocorticoid hormones, a 72-h pretreatment with E2 failed to potentiate GRF-induced cAMP accumulation or enhance the sensitivity of the GH response to GRF. However, E2 increased the stimulatory effect of submaximal concentrations of dexamethasone on spontaneous and GRF-induced GH release as well as on total GH, but did not further increase the effect of maximal dexamethasone concentrations. As determined by a 60-min pulse labeling with [35S]methionine performed after a 72-h preincubation with E2, GH and PRL synthesis were increased by about 50% above control values (P less than 0.005). The present data clearly indicate for the first time that E2, at physiological concentrations, exerts a stimulatory effect on spontaneous and GRF-induced GH release as well as on cellular GH content, probably resulting, at least in part, from stimulation of GH synthesis.

Animals↗
PubMed1985

Keoxifene shows pure antiestrogenic activity in pituitary gonadotrophs.

Estrogens increase both basal and LHRH-induced LH release in rat anterior pituitary cells in culture. Following 48 h of preincubation with 1 nM 17 beta-estradiol, the maximal LH response to LHRH is increased 1.5-fold while the ED50 value of LHRH action is decreased 2.5-fold from 500 to 200 pM. The maximal 3-fold stimulation of 0.3 nM LHRH-induced LH release by 17 beta-estradiol is exerted at a KD value of 14.4 pM. Keoxifene (300 nM) completely blocks the potent stimulatory effect of 17 beta-estradiol up to 1 nM, the highest concentration of the estrogen used. As shown by the complete reversal of the stimulatory effect of 0.1 and 1.0 nM 17 beta-estradiol by keoxifene at IC50 values of 7.7 and 34 nM respectively, the antiestrogen interacts competitively with 17 beta-estradiol at the estrogen binding site. When present alone, keoxifene shows no estrogenic activity. The present data show that keoxifene acts as a pure antiestrogen on the control of LHRH-induced LH release in rat pituitary gonadotrophs.

Animals↗