Multiple factors controlling ACTH secretion at the anterior pituitary level.
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Adenylyl Cyclases↗
Biomedical subjects
F Labrie
Publications and source records attributed to F Labrie.
Morphological studies of the canine pituitary luteinizing hormone (LH) cells after long-term treatment with the LH-releasing hormone (LHRH) agonist [D-Trp6]LHRH ethylamide.
Since treatment with LHRH agonists (LHRH-A) cause changes in LH secretion which are similar in both man and dog, we have studied cytological changes occurring in canine LH cells after chronic administration of an LHRH-A, [D-Trp6] LHRH ethylamide. At the light microscopic level, LH cells were distributed evenly in the gland, but showed a decrease in cell surface area of 10% after 1 month and 23% after 4 months of daily injection of 50 micrograms LHRH-A. At the electron microscopic level, the gonadotrophs from control animals were characterized by the presence of two types of secretory granules and a dilatation of the rough endoplasmic reticulum. Immunostaining for LH was localized only to secretory granules. LHRH-A administration caused the appearance of glycogen in the cytoplasm. Four months after cessation of the treatment, the gonadotrophs showed a normal cytological appearance, thus indicating full reversibility of the morphological changes induced by long-term treatment with an LHRH-A.
Animals↗
Morphological study of the effects of an GnRH agonist on the canine testis after 4 months of treatment and recovery.
After 4 months of treatment of adult male dogs with the GnRH agonist (GnRH-A) [D-Trp6]GnRH ethylamide, the seminiferous tubules contained only type A and B spermatogonia, Sertoli cells, and rare primary spermatocytes, thus causing a 64% decrease in testis weight. At the electron microscope level, Sertoli cells showed an increase in phagosomes and lipid droplets. Leydig cells were markedly atrophied with the accumulation of lipid droplets and showed a predominance of mitochondria with lamellar instead of vesicular cristae. Four months after cessation of treatment with GnRH-A, a complete return to normal spermatogenesis and Leydig cell morphology was observed. The full reversibility of spermatogenesis in the dog after chronic GnRH-A treatment suggests that this well-tolerated peptide could be used as a reversible method of male contraception.
Animals↗
Effects of flutamide, a pure antiandrogen, on endocrine parameters, in the adult female rat.
Since antiandrogens having mixed agonistic-antagonistic activities on the androgen receptor have shown benefits in the treatment of hirsutism, the availability of a pure antiandrogen is of particular interest. As a first step, we have thus investigated in detail the effect of the pure antiandrogen Flutamide on endocrine parameters in the female rat. Treatment with the antiandrogen (5 mg, twice daily) for 4 cycles did not affect the 4-day estrous cycle. The antiandrogen had no significant effect on the ovarian level of cytosolic total and available as well as nuclear estrogen receptors in the uterus, and did not affect the concentration of LH and FSH ovarian receptors. The ovarian level of progestins was minimally affected or unchanged on estrus and diestrus I, while an increase was observed under treatment with Flutamide on diestrus II and proestrus. In the plasma, however, there was small or no effect of Flutamide treatment on the concentration of pregnenolone, 17-OH pregnenolone, progesterone and 17-OH-progesterone. The ovarian levels of testosterone (T) and of its two metabolites androstane-3 alpha,17 beta-diol and androstane-3 beta,17 beta-diol were increased by treatment with Flutamide on the morning of diestrus II and proestrus. This was reflected by a 30-100% increase of the levels of plasma T on proestrus. The increase in the ovarian concentration of 5-androstene-3 beta,17 beta-diol (delta 5-diol) and androstenedione observed on diestrus II and on proestrus did not lead to any change in the plasma level of these steroids, which remained normal throughout the estrous cycle during treatment with Flutamide. The ovarian and plasma levels of 17 beta-estradiol were not affected by treatment with the antiandrogen. The present data show that treatment of intact adult female rats with the pure antiandrogen Flutamide has no effect on the estrous cycle, with no significant change in the plasma concentration of the most important estrogenic compound in the rat, namely, 17 beta-estradiol. The present observation of minor endocrine effects of Flutamide in the intact adult female rat supports clinical trials on the use of this antiandrogen, a potential drug of choice for the treatment of hirsutism, acne and alopecia in women.
17-alpha-Hydroxyprogesterone↗
New concepts on the androgen sensitivity of prostate cancer.
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Adrenalectomy↗
Estrogenic activity of phenol red in rat anterior pituitary cells in culture.
The estrogenic activity of phenol red, a pH indicator widely used in cell culture media, was studied in rat anterior pituitary cells. After 72 hours of incubation with 40 microM phenol red, a 40-50% increase in prolactin cell content and a 100% stimulation of luteinizing hormone-releasing hormone induced luteinizing hormone release was observed. Both effects could be completely reversed by simultaneous incubation with the antiestrogen LY156758. In the rat uterine [3H] estradiol binding assay, phenol red showed a significant displacement at concentrations above 10 microM while its concentration in the commonly used culture media is about 40 microM. From the present results, we conclude that phenol red acts as a weak estrogen in normal tissues and that its estrogenic activity should be taken into account in studies using estrogen-sensitive cell or tissue cultures.
Animals↗
Combination therapy in prostate cancer.
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Combined Modality Therapy↗
Combination therapy in prostate cancer.
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Combined Modality Therapy↗
A wide range of sensitivities to androgens develops in cloned Shionogi mouse mammary tumor cells.
Clones obtained in soft agar from a Shionogi mouse mammary carcinoma show marked heterogeneity of growth characteristics and sensitivities to androgens. These data pertain to spontaneous growth in the absence of androgens, maximal response to dihydrotestosterone (DHT) and Km values of the stimulatory action of DHT ranging from 0.008 to 10 ng/ml (1,250-fold range). Following 13 months in culture in the presence of 10 nM DHT, recloning of one original cell clone led to an even greater variation of androgen-free growth and of the maximal responses to DHT, while the Km values of DHT action ranged from 0.05 to 10 nM (200-fold range). The present demonstration of a marked heterogeneity of Km values of DHT action in subpopulations of tumors grown in a controlled environment has major implications for the efficient antihormonal treatment of androgen-sensitive diseases such as prostate cancer. Such data indicate that cell clones having a high degree of sensitivity to DHT (androgen-hypersensitive) can continue to grow in the presence of castration levels of androgens, thus suggesting that an antiandrogen is required in order to achieve a more complete androgen blockage and to induce a regression of these androgen-hypersensitive tumors.
Animals↗
Characteristics of the beta-adrenergic stimulation of adenylate cyclase activity in rat ventral prostate and its modulation by androgens.
Beta-adrenergic agents cause a 2.5-3-fold stimulation of adenylate cyclase activity in rat ventral prostate membrane preparations with an order of potency (KD values) typical of a beta 2-subtype receptor: (-)isoproterenol (20 nM) greater than (-)epinephrine (70 nM) much greater than (-)norepinephrine (1 microM) much greater than dopamine (70 microM). The stimulatory effect exerted by high concentrations of dopamine (greater than 0.1 mM) is completely reversed by propranolol but not by haloperidol or sulpiride, thus indicating an action of dopamine mediated by the beta-adrenergic receptor. One week after castration, basal adenylate cyclase activity in prostatic membranes is 50% reduced. In the same group, the stimulation by isoproterenol is completely abolished in the absence of GTP, while the effect of GTP alone is reduced by 75%. The inhibitory effect of castration on basal as well as isoproterenol- and GTP-stimulated adenylate cyclase activity can be completely reversed by treatment of castrated animals with dihydrotestosterone, thus demonstrating the marked androgen dependency of adenylate cyclase activity in prostatic tissue. Since the response to direct stimulation of adenylate cyclase activity (assessed by NaF and forskolin) is only reduced by 33%-60% while the response to isoproterenol is 100% abolished, the present data indicates that the complete loss of beta-adrenergic responsiveness of prostatic adenylate cyclase following castration includes many steps, including those preceding adenylate cyclase activity, namely the beta-adrenergic receptor itself and/or its coupling via the GTP-binding protein. The large amplitude of the effects observed should facilitate study of the mechanisms involved in the marked regulation of the beta-adrenergic receptor-adenylate cyclase system by androgens in prostatic tissue.
Adenylyl Cyclases↗
Adrenal steroids stimulate growth and progesterone receptor levels in rat uterus and DMBA-induced mammary tumors.
We have studied the effect of treatment with the adrenal steroids androst-5-ene-3 beta,17 beta-diol (delta 5-diol) and dehydroepiandrosterone (DHEA) on the growth and progesterone receptor levels of dimethylbenz(a)anthracene (DMBA)-induced mammary tumors in the rat. While the total number of tumors in ovariectomized animals was 0.60 +/- 0.19 tumor per rat after 24 days, it increased to 2.54 +/- 0.50 (p less than 0.01) and 1.42 +/- 0.26 (p less than 0.01) in the delta 5-diol and DHEA (2 mg, twice daily) treated animals, respectively. While very few new tumors developed during a 24-day period in ovariectomized animals (0.07 +/- 0.07/rat), an average of 0.47 +/- 0.19 (p less than 0.05) new tumor per animal appeared in intact rats. In ovariectomized animals treated with delta 5-diol or DHEA, the numbers of new tumors were 0.77 +/- 0.26 (p less than 0.05) and 0.42 +/- 0.15 (p less than 0.05), respectively. An even more striking effect was observed on average total tumor area, which decreased from 4.70 +/- 0.95 cm2 in intact animals to 0.75 +/- 0.27 cm2 (p less than 0.01) following ovariectomy. Values of 9.79 +/- 2.25 (p less than 0.01) and 3.93 +/- 0.86 cm2 (p less than 0.01) were found in the delta 5-diol- and DHEA-treated ovariectomized animals, respectively. Treatment of ovariectomized animals with delta 5-diol and DHEA caused a marked increase (p less than 0.01) in progesterone receptor levels in both the uteri and DMBA-induced mammary tumors. Uterine weight was also stimulated (p less than 0.01) by treatment with the two adrenal steroids.(ABSTRACT TRUNCATED AT 250 WORDS)
9,10-Dimethyl-1,2-benzanthracene↗
Advantages of the combination therapy in previously untreated and treated patients with advanced prostate cancer.
In order to achieve a more complete blockade of androgens of both testicular and adrenal origin at the start of treatment, we have administered the pure antiandrogen Flutamide in association with orchiectomy (13 patients) or the LHRH agonist [D-Trp6]LHRH ethylamide (118 patients) to previously untreated patients with clinical stage D2 prostate cancer. The mean duration of treatment was 491 days (102-1208 days). The response was assessed according to the criteria of the U.S. National Prostatic Cancer Project. A complete response has been observed in 30 patients (23%) while partial and stable responses have been achieved in 50 (38%0 and 45 (34%) patients, respectively. A positive objective response has thus been observed in 125 of 131 patients (95%). Serum PAP became normal before 6 months in all except 8 (6.1%) of patients. Quite remarkably, 23 of 48 patients treated for 2 years (47.9%) have achieved a complete response. Of the 20 deaths, 12 (9%) were due to prostate cancer, while 8 (6%) resulted from other causes. The probability of continuing a positive response after 2 years of treatment (according to Kaplan and Meier) is 60% while the probability of survival at the same time interval is 89%. This survival should be compared to values of approx 50% achieved with previous treatments limited to inhibition of testicular androgen secretion or action. The present data demonstrate that the combined blockade of androgens achieved with Flutamide and castration provides an objective response in approx 95% of patients, and markedly prolongs the period of remission while the death rate within the first 2 years is lower than that obtained with previous treatments. The important prolongation of survival is achieved with an excellent quality of life. Two-hundred and three patients have clinical stage D2 prostate cancer previously treated by orchiectomy, estrogens or LHRH agonists alone received, at the time of relapse, the same combination therapy. Patients already castrated received only Flutamide while, for those previously treated with DES, the estrogen was replaced by the LHRH agonist [D-Trp6]LHRH ethylamide in association with Flutamide. Flutamide was given as additional medication to those already receiving an LHRH agonist alone. Complete, partial and stable objective responses assessed according to the criteria of the U.S. National Prostatic Cancer Project were obtained in 11 (5.4%), 17 (8.4%) and 38 (18.7%) patients, respectively, for a total objective response rate of 32.5%. Progression continued in 137 (67.5%) patients.(ABSTRACT TRUNCATED AT 400 WORDS)
Androgen Antagonists↗
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↗
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↗
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↗
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↗
Characteristics of the beta-adrenergic receptor in the rat ventral prostate using [125I]cyanopindolol.
The binding characteristics of the beta-adrenergic receptor in the rat ventral prostate homogenate have been studied using the highly potent beta-adrenergic antagonist [125I]cyanopindolol (CYP) as ligand. The bound ligand was separated from the free moiety by precipitation with polyethylene glycol (PEG-6000). This technique is simple, accurate, fast and more advantageous than filtration of the hormone-receptor complex on glass fiber filters or direct centrifugation. [125I]CYP binds to a single class of high affinity sites at an apparent KD value of 23 pM. Using 0.1 microM (-)propranolol to determine non-specific binding, a number of sites of 600 fmol/mg protein were measured. The observed order of potency of adrenergic agonists (KD values) in competing for [125I]CYP binding was: (-)isoproterenol (25 nM) greater than (-)epinephrine (74 nM) much greater than (-)norepinephrine (1900 nM). Detailed study of the binding potency of a large series of beta 1- and beta 2-adrenergic agonists and antagonists showed the presence of a typical beta 2-subtype adrenergic receptor in the rat ventral prostate. The best estimate indicates that the proportion of beta 2-adrenergic receptors in rat ventral prostate is more than 95% of the total population of beta-adrenergic receptors in this tissue. The high selectivity and density of beta 2-adrenergic receptors in rat ventral prostate suggest a physiological role of circulating and/or locally secreted catecholamines in the control of prostatic growth and function.
Adrenergic beta-Antagonists↗
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↗