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Biomedical subjects

M Grino

Publications and source records attributed to M Grino.

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

Ontogeny of expression of the corticotropin-releasing factor gene in the hypothalamic paraventricular nucleus and of the proopiomelanocortin gene in rat pituitary.

The ontogeny of expression of the CRF gene in the paraventricular hypothalamic nucleus and POMC gene in the pituitary was studied in rats using in situ hybridization histochemistry and Northern blotting techniques, respectively. CRF mRNA was first detected on day 17 of gestation (E17) in the paraventricular nucleus of the hypothalamus. The levels of hypothalamic CRF mRNA increased progressively from E17 to E19-E20, decreased during the perinatal period, and increased thereafter. The levels of POMC mRNA in the pituitary paralleled the variations in hypothalamic CRF mRNA, showing a peak on E20-E21. POMC mRNA levels in the anterior pituitary were decreased on days 4-7 after birth (P4-P7) and increased steadily thereafter. In contrast to levels in the anterior pituitary, POMC mRNA levels increased steadily from P1 to P21 in the neurointermediate lobe of the pituitary. These data indicate that the expression of both the CRF and POMC genes in the paraventricular nucleus and anterior pituitary, respectively, are reduced during the first week of life, i.e. within the so-called stress nonresponsive period. Our observations suggest that an impaired regulation of ACTH and CRF synthesis due to an immature neuronal pathway within the brain or increased glucocorticoid feedback may account for the stress nonresponsive period.

Animals↗
PubMed1989

Onset of glucocorticoid responsiveness of anterior pituitary corticotrophs during development is scheduled by corticotropin-releasing factor.

Expression of the CRF gene in the hypothalamus and that of the POMC gene in the anterior pituitary are reduced during the first week of life in the rat. During this so-called stress nonresponsive period (SNRP), stimuli such as ether vapors, electroshocks, and hypoxia do not elicit ACTH secretion from the pituitary, as occurs later in development. The current hypothesis to explain the SNRP is an increased negative glucocorticoid feedback on POMC and CRF synthesis and/or release during this time. To test this hypothesis we studied the effects of adrenalectomy (ADX) on anterior pituitary POMC mRNA expression. In 7-day-old rats POMC mRNA levels were increased only 3-fold 48 h post-ADX, compared to a 7-fold increase in 14-day-old animals. This blunted effect of endogenous glucocorticoid removal on pituitary POMC mRNA could be due to decreased up-regulation of CRF after removal of glucocorticoids or normal up-regulation of CRF but decreased pituitary responsiveness to CRF relative to those in 14-day-old animals. Therefore, we studied in vitro beta-endorphin release from pituitaries obtained from 7- and 14-day-old rats. CRF stimulated basal beta-endorphin release to the same extent in pituitaries from both groups. The inhibition by corticosterone of CRF-stimulated beta-endorphin secretion was also indistinguishable in pituitaries obtained from 7- or 14-day-old rats. Since the responsiveness of the 7-day-old pituitary was normal, the blunted enhancement of POMC biosynthesis after ADX must be mediated at the level of the hypothalamus. Indeed, in situ hybridization showed that while in 14-day-old rats ADX induced a significant increase [190 +/- 10% (+/- SE) of control; n = 5; P less than 0.0005] in hypothalamic mRNA levels, ADX did not change the expression of the CRF gene in the paraventricular nucleus of 7-day-old rats, indicating a lack of glucocorticoid modulation of hypothalamic CRF synthesis. Finally, we studied the effects of 48 h CRF treatment on the post-ADX increase in POMC mRNA levels in 7-day-old rats. Daily injections of 200 ng CRF/rat induced an increase in anterior pituitary POMC mRNA concentrations [669 +/- 139% (+/- SE) of control; n = 6; P less than 0.02 vs. adrenalectomized vehicle-treated rats] comparable to that in adrenalectomized untreated 14-day-old rats. In conclusion, our data indicate that the glucocorticoid regulation of hypothalamic CRF gene expression is not mature during the first week of life, i.e. within the so-called SNRP.(ABSTRACT TRUNCATED AT 400 WORDS)

Adrenalectomy↗
PubMed1989

Dexamethasone induces an increased biosynthesis of chromogranin A in rat pituitary gland.

The influence of dexamethasone on the regulation of the biosynthesis of chromogranins A and B, two proteins originally described in adrenal chromaffin granules, was investigated in the rat pituitary gland. Dexamethasone increased chromogranin A levels and its corresponding mRNA in a dose-dependent manner. Induction of chromogranin A occurred with a time-lag of 24 h. As shown by immunohistochemistry, chromogranin A was present in control and dexamethasone-treated rats in gonadotrophic cells only. Chromogranin B, secretogranin II and the respective pituitary hormones co-stored with chromogranin A were not changed by dexamethasone. Thus dexamethasone selectively increased chromogranin A levels in gonadotrophic cells.

Animals↗
PubMed1988

Secretion of corticotropin releasing factor (CRF) and vasopressin (AVP) into the hypophysial portal blood of conscious, unrestrained rams.

The secretion of Corticotropin-Releasing Factor (CRF) and Arginine Vasopressin (AVP) into sheep hypothalamo-hypophysial portal blood was investigated in conscious, unrestrained castrated rams. One to two hours after the onset of the collection, peripheral ACTH and cortisol levels were within the basal range in all the animals and portal CRF and AVP concentrations were low ranging between 5 and 90 pg/ml. After acute hemorrhage, a sharp increase in portal CRF and AVP was observed, inducing a sustained elevation of peripheral ACTH and cortisol. These data show that measurements of CRF and AVP in the portal blood of conscious sheep provide a good methodology to study the regulation of basal and stress-induced ACTH secretion.

Animals↗
PubMed1988

Human placenta and the hypothalamic-pituitary-adrenal axis.

Maternal plasma bound and free cortisol rises during pregnancy, while maternal plasma IR-ACTH is initially low but soon rises inspite of the further increase of plasma free cortisol. This rise of plasma ACTH during pregnancy, can not be attributed to changes of plasma levels of estrogens or progesterone. It is possible that the human placenta is responsible for the rise in maternal plasma ACTH during pregnancy. There are two possible mechanisms by which this effect could occur: 1) by the placental secretion of CRH into the maternal circulation, which stimulates the maternal pituitary to secrete ACTH, and 2) the secretion of placental POMC-derived peptides. Recent data indicate that the human placenta is capable of both of these actions: A) The POMC and CRH genes are expressed in human placenta; B) the human term placenta is able to secrete both CRH and POMC-derived peptides in vitro; C) the CRH present in the plasma of pregnant women is bioactive and in sufficient levels to be effective on maternal pituitary; D) synthetic hCRH can stimulate the release of placental POMC peptides in vitro. We conclude that the human placenta may be a modulator of the HPA axis during pregnancy in a number of possible ways. Additional experimental work should clarify the intriguing interaction between the HPA axis and the human placenta during pregnancy, labor and delivery.

Adrenocorticotropic Hormone↗
PubMed1988

Maturation of the pituitary-adrenal function in rat fetuses.

Plasma adrenocorticotropic hormone (ACTH) and corticosterone were detectable in fetal plasma on day 16 of pregnancy. Thereafter, the levels of both hormones increased steadily in a parallel manner and reached a peak on day 19 of pregnancy. Administration of an antiserum anti-rat corticotropin-releasing factor (CRF) to pregnant rats was followed by a significant decrease in fetal plasma corticosterone as early as day 17. Plasma ACTH measured under the same experimental conditions on day 19 of gestation was also significantly decreased. Similar results have been obtained with fetal plasma collected from adrenalectomized pregnant rats, indicating that the plasma corticosterone decrease in fetuses after immunoneutralization of CRF reflects changes in fetal adrenal secretion and not a diminution of corticosterone transfer from the maternal to the fetal circulation. These results show that endogenous CRF begins to play a physiological role in the regulation of ACTH and corticosterone secretion as early as in 17-day-old fetuses. This effect may occur before the connections between the neurosecretory CRF axons and the hypophysial portal capillaries have been established. Therefore, endogenous CRF may enter the hypophysial portal circulation after intercellular diffusion in hypothalamic tissue.

Adrenocorticotropic Hormone↗
PubMed1988

In vitro corticotropin-releasing hormone (CRH) stimulation of adrenocorticotropin release from corticotroph adenoma cells: effect of prolonged exposure to CRH and its interaction with cortisol.

To examine if down-regulation of CRH-induced ACTH release occurs in corticotroph adenoma cells as well as CRH-glucocorticoid interactions in these cells, we established primary cultures of pituitary adenoma cells obtained by transphenoidal surgery from five patients with Cushing's disease. To prevent binding of glucocorticoids by serum proteins, we used a serum-free medium containing insulin, transferrin, selenium, and epidermal growth factor. The latter was found to be essential for both basal and CRH-stimulated ACTH secretion. CRH acutely stimulated, in a dose-dependent manner, ACTH release by all adenomas studied, with an IC50 of 0.5 X 10(-9) mol/L. Prolonged exposure (10 days) to a half-maximal stimulatory concentration of CRH led to continuous stimulation of ACTH secretion. A 4-day incubation with cortisol induced a dose-dependent decrease in both basal and long term CRH-stimulated ACTH release, with no difference in the IC50 (1 X 10(-8) mol/L). These data suggest that long term exposure to CRH does not desensitize corticotroph adenoma cells. Thus, it is unlikely that long-acting analogs of CRH will be useful in the treatment of Cushing's disease. ACTH secretion from corticotroph adenomas is restrained by glucocorticoids; the sensitivity of these cells to the negative effect of glucocorticoids is not modified by long term stimulation with CRH.

Adenoma↗
PubMed1988

Corticotropin-releasing hormone and oxytocin stimulate the release of placental proopiomelanocortin peptides.

Human placenta contains the POMC-derived peptides ACTH, alpha MSH, and beta-endorphin, and CRH. High concentrations of immunoreactive (IR) CRH have been recently demonstrated in maternal plasma during pregnancy. To determine if the human placenta secretes CRH and POMC-derived peptides, we developed an in vitro human placental fragment perifusion system. The perifused tissue released IR-CRH and POMC-derived peptides at a constant rate for at least 5 h. The mean IR-CRH concentration in the effluent (under basal conditions) was 158 +/- 26 (+/- SD) pg (34.5 +/- 5.8 fmol)/5-min fraction.g tissue. IR-alpha MSH, IR-beta-endorphin, and IR-ACTH were also released into the perifusion medium; the mean concentration of alpha MSH released was 24.6 +/- 8 pg (14.8 +/- 4.8 fmol)/fraction.g, that of ACTH was 2.9 +/- 1.9 pg (0.65 +/- 0.43 fmol)/fraction.g, and that of beta-endorphin was 12.9 +/- 6 pg (3.8 +/- 1.7 fmol)/fraction.g. We examined the effects of human CRH, oxytocin, vasopressin, and dexamethasone on placental POMC peptide secretion. Five-minute pulses of 10(-8) or 10(-6) mol/L human CRH or oxytocin produced an immediate and dose-dependent increase in all POMC peptides in the effluent. A 5-min pulse of 10(-8) or 10(-6) mol/L vasopressin had no effect. A continuous 4-h exposure to 10(-6) mol/L dexamethasone had no effect on either basal IR-CRH or POMC-derived peptide or their KCl-induced release. In conclusion, we found that 1) human placenta releases IR-CRH and POMC-derived peptides in vitro; this phenomenon seems to be independent of glucocorticoid control; 2) placental CRH may have a paracrine effect on placental POMC peptide release in addition to its possible action on maternal pituitary hormone release; and 3) oxytocin, but not vasopressin, stimulates placental POMC peptide release.

Adrenocorticotropic Hormone↗
PubMed1988

Characterization of corticotropin-releasing hormone receptors on human pituitary corticotroph adenomas and their correlation with endogenous glucocorticoids.

Specific receptors for CRH were identified in five freshly excised pituitary adenomas causing Cushing's disease. Their kinetic properties and mean affinity constant [1.45 +/- 0.38 (+/- SE) nmol/L] were comparable to the characteristics of rat and monkey anterior pituitary CRH receptors. No correlation was found between the immediate preoperative plasma and urinary cortisol levels and the number of pituitary adenoma CRH receptors, which ranged from 6-96 fmol/mg protein, unlike in rats, in which corticosterone modulates the number of anterior pituitary CRH receptors. The lack of correlation between the concentration of CRH receptors and plasma cortisol levels may reflect the inability of glucocorticoids to down-regulate CRH receptors in these tumors. Thus, corticotroph adenomas are resistant not only to the feedback actions of glucocorticoids on proopiomelanocortin synthesis and secretion but also to their actions on CRH receptors.

Adenoma↗
PubMed1988

[Cushing's syndrome caused by ectopic production of CRF by a medullary carcinoma of the thyroid body].

A 58-yr-old man presented a Cushing's syndrome gradually developed for two years, and a cervical tumor. Urinary free cortisol and 17-hydroxy-corticosteroids were elevated and non suppressible under high dose dexamethasone (8 mg a day X 2 days). Plasma calcitonin (7,200 pg/ml), CEA (803 ng/l), beta LPH (624 pg/ml), and CRF (29 pg/ml) were elevated. Total thyroidectomy revealed a medullary carcinoma of the thyroid. Postoperatively the Cushing's syndrome disappeared and plasma CRF became undetectable although plasma calcitonin remained elevated. One out of 3 CRF antisera tested for immunocytology was positive in 10 to 30% of the cells. In tumor extract, CRF (RIA) concentration was 4.75 ng/g. There was no detectable ACTH in the tumor by biochemical as well as immunocytochemical method. In the present report, the next evidences are--for the first time--simultaneously present to demonstrate an ectopic secretion of CRF by a medullary thyroid carcinoma: presence of CRF in systemic blood being undetectable after surgery; cure of the clinical and biological features of Cushing's syndrome after thyroidectomy; characterization of CRF immunoreactivity in tumor. Taken together, the radioimmunological and the immunocytochemical data suggest the production of several molecular forms of CRF.

Carcinoma↗
PubMed1988

Carcinoma of the prostate with Cushing's syndrome. A case report with histochemical and chemical demonstration of immunoreactive corticotropin-releasing hormone in plasma and tumoral tissue.

A case is described of a patient with a small-cell prostatic carcinoma containing immunoreactive CRH, in conjunction with ACTH-dependent Cushing's syndrome. The serum concentrations of CRH, ACTH, beta-endorphin and calcitonin were all found to be above normal. Post-mortem examination revealed a prostatic tumour with multiple metastases, and a diffuse hyperplasia of pituitary corticotropic cells and adrenal cortical cells. In sections of the primary prostatic tumour, immunoreactive cells were demonstrable with antisera raised against human CRH, TSH, calcitonin and somatostatin, but not with antisera against ACTH or beta-endorphin. By radioimmunoassay the CRH-like material could also be demonstrated in extract of the prostatic tumour and the material from both plasma and tumour extract eluted at the position of human CRH on gel chromatography (Sephadex G-75). These findings provide support for the interpretation that the patient's Cushing's syndrome was due to a CRH-producing prostatic tumour. Finally, the origin and the clinical significance of the neuroendocrine cells in the prostatic carcinoma is discussed.

Adenocarcinoma↗
PubMed1987

The corticotropin releasing hormone gene is expressed in human placenta.

Maternal plasma immunoreactive corticotropin-releasing hormone (IR-CRH) increases progressively with pregnancy. This elevated plasma IR-CRH is presumably secreted by the placenta. To investigate further this hypothesis, we searched for the CRH mRNA and its peptide product in full term human placentae. Using a radiolabelled 48-mer oligonucleotide probe complementary to a portion of human CRH mRNA, we identified a 1300 nucleotide RNA from human placenta and rat hypothalami. We next examined the chromatographic characteristics of the placental IR-CRH. The bulk of the IR-CRH extracted from placenta and the IR-CRH secreted in vitro by placental fragments had the same chromatographic profiles as synthetic CRH. These findings indicate that the CRH gene is expressed in human placenta and imply that this organ is a site of CRH biosynthesis during pregnancy.

Chromatography, Gel↗
PubMed1987

Evidence for basal and stress-induced release of corticotropin releasing factor in the push-pull cannulated median eminence of conscious free-moving rats.

Fourteen adult male rats were successfully implanted in their median eminence with a push-pull cannula perfusing an artificial fluid at a rate of 13 microliters/min, to measure the release of corticotropin releasing factor (rCRF-41) under physiological conditions assessed by baseline plasma adrenocorticotropic hormone (ACTH) levels. In the basal conscious free-moving state, rCRF-41 release displayed a fluctuating pattern, with peaks about every 45 min at a mean value of 9.0 +/- 0.7 pg/15 min sample (n = 42) vs a mean trough value of 4.1 +/- 0.3 pg/sample (n = 44). Ether stress was followed by a striking rise in rCRF-41 release which generally lasted about 45 min and reached mean peak values of 54.3 +/- 3.2 pg/15 min sample (n = 7). These data constitute the first direct measurements of basal and stress-induced CRF releases in conscious unrestrained rats.

Adrenocorticotropic Hormone↗
PubMed1987

Effect of passive immunization against corticotropin-releasing factor (CRF) on the postadrenalectomy changes of CRF binding sites in the rat anterior pituitary gland.

The concentration of corticotropin-releasing factor (CRF)-binding sites decreases in the rat anterior pituitary after adrenalectomy; this change may be related either to a direct effect of the circulating glucocorticoids at the pituitary level or to a desensitization of CRF receptors through an increased CRG release in hypophysial portal blood. In order to examine the latter possibility we have measured plasma adrenocorticotropin hormone (ACTH) levels and the number of anterior pituitary CRF binding sites in sham-operated and 24-hour adrenalectomized rats after blockade of endogenous CRF by passive immunization with an antiserum anti-rat CRF (CRF-AS), or after injection of normal rabbit serum (NRS). In NRS-injected rats, after sham operation, plasma ACTH concentration increased (227 +/- 34 vs. 118 +/- 19 pg/ml in controls) without change in CRF-binding sites capacity (20.7 +/- 2.6 vs. 24.6 +/- 3.5 fmol/mg protein in controls). Adrenalectomy induced a large rise in plasma ACTH (785 +/- 89 pg/ml) and a decrease in the number of CRF-binding sites (12.2 +/- 1.7 fmol/mg protein). After CRF-AS injection, plasma ACTH was normalized in sham-operated animals (149 +/- 24 pg/ml) and significantly reduced in adrenalectomized rats (472 +/- 76 pg/ml); the adrenalectomy-induced decrease in the number of CRF-binding sites was unaffected by the CRF-AS administration (12.2 +/- 1.7 fmol/mg protein). The administration of dexamethasone to adrenalectomized rats significantly reduced plasma ACTH concentrations (23.3 +/- 10.6 pg/ml) and prevented the loss in CRF-binding sites capacity (20.7 +/- 1.3 fmol/mg protein).(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenalectomy↗
PubMed1987

The corticotropin-releasing factor release in rat hypophysial portal blood is mediated by brain catecholamines.

In order to study the involvement of the hypothalamic corticotropin-releasing factor (CRF) in catecholamine-induced adrenocorticotropin (ACTH) secretion, we have measured CRF levels in rat hypophysial portal blood (HPB) after the pharmacological destruction of the ventral noradrenergic bundle (VNAB), using 6-hydroxydopamine (6-OHDA) stereotaxically injected into the VNAB. CRF levels in HPB were measured by radioimmunoassay, and the effects of 6-OHDA injection were controlled by the determination of catecholamine concentrations in the total hypothalamus. VNAB lesions induced a dramatic decrease in norepinephrine and epinephrine hypothalamic concentration. The CRF levels in HPB were also significantly reduced. These results suggest that central catecholamines exert a direct stimulatory control on the CRF release and play a major role in stress-induced ACTH secretion.

Adrenocorticotropic Hormone↗
PubMed1987

[Methods of hypothalamo-hypophyseal portal blood collection].

It is possible to assay hypothalamic factors in hypophysial portal blood from several species. However, hypophysial portal blood collection must be performed after anesthesia and surgical stress which can both modify the regulation of hypothalamo-pituitary secretion. However, this method has allowed some progress in our knowledge of the hypothalamic control of pituitary secretion. The methodology, advantages and limits of hypophysial portal blood collection are briefly described in this review.

Animals↗
PubMed1986

[Characterization and modulation of anterior pituitary binding sites for rat corticotropin releasing factor (r-CRF)].

Specific binding sites for rat CRF (r-CRF) have been characterized on rat anterior pituitary membranes. The binding of the radioiodinated analog of r-CRF (125I Tyr-r-CRF) was time, temperature, pH and protein dependent. No interaction was found with other neurohormones except with Arginine Vasopressin, but at supra physiological levels. Two classes of specific binding sites (high affinity and low affinity) for r-CRF were identified. Bilateral adrenalectomy provoked, since the 24th hour and up to 7 days, in addition of an increase of ACTH plasmatic levels, an abolition of the high affinity binding site; corticosterone treatment reversed these changes. This finding suggests that circulating glucocorticoids may control the anterior pituitary binding sites for CRF, either by a direct action on the anterior pituitary, or by a modulatory effect on hypothalamic CRF secretion.

Adrenalectomy↗