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M Grino

Publications and source records attributed to M Grino.

At least 55 records · Page 3Linked to original sources
PubMed1992

Effect of chronic active immunization anti-corticotropin-releasing factor on the pituitary-adrenal function in the sheep.

ACTH and cortisol diurnal variations and responses to two types of stress (insulin-induced hypoglycemia and isolation-restraint stress) or to an acute injection of lysine-vasopressin were studied in intact and anti-corticotropin-releasing factor (CRF) actively immunized rams. Immunization was obtained by the injection of synthetic ovine CRF coupled to BSA with carbodiimide. All animals developed antibodies anti-CRF and displayed an alteration of their general condition and a body weight reduction. The mean basal ACTH and cortisol secretion as well as the number and mean amplitude of diurnal pulses of these hormones was significantly reduced in the group of anti-CRF immunized rams. However, the reduction in all three parameters was much more pronounced for cortisol than for ACTH. No ACTH and cortisol response to insulin-induced hypoglycemia and isolation-restraint stress was observed. The stimulating action of lysine-vasopressin on ACTH release was significantly reduced as compared to controls. These results indicate that CRF is a major physiological component of the ovine hypothalamo-hypophysial-adrenal axis and participates in the events that regulate ACTH and cortisol diurnal variations and response to stress.

Adrenocorticotropic Hormone↗
PubMed1992

Stimulation of adrenocorticotropin secretion by insulin-induced hypoglycemia in the developing rat involves arginine vasopressin but not corticotropin-releasing factor.

In the neonatal rat, the response of the hypothalamo-pituitary-adrenal axis to stressful stimuli is markedly decreased during the first 2 weeks of life. This peculiar period was named "stress hyporesponsive period." In this report, we studied the effect of insulin-induced hypoglycemia, known as a strong stimulator of the corticotroph function in the adult rat. Rats (8- or 20-day-old) were injected ip with 3 IU/kg synthetic insulin and were killed at various times. In 20-day-old rats, hypoglycemia induced a rapid drop in blood glucose concentrations accompanied by a stimulation of ACTH and corticosterone secretion which reached maximal values within 30 min. On the opposite, in 8-day-old rats, despite a rapid decrease in blood glucose levels, insulin injection induced a gradual rise of plasma ACTH and corticosterone concentrations which peaked at 90 min. This delayed response of the hypothalamo-pituitary-adrenal axis to hypoglycemia in the youngest rats does not seem to be due to a difference of sensitivity to insulin-induced hypoglycemia since injection of increasing doses of insulin (0.3, 0.75, or 3 IU/kg body wt) induced a dose-related decrease of blood glucose concentrations and a rise in plasma ACTH and corticosterone levels, comparable in the two age group studied. Basal or hypoglycemia-stimulated absolute corticosterone values were much lower in 8-day-old rats than in 20-day-old animals, suggesting an immaturity of the adrenal glands in the youngest animals. Daily ACTH injection, starting 3 days before the experiment, had a trophic effect on the adrenal glands leading to a more important increase of corticosterone levels after hypoglycemia in 8-day-old rats. Our results confirm that there is an immaturity of the adrenal glands in young rats, probably due to the low plasma ACTH levels during the neonatal period. To determine the respective role of the two major hypothalamic ACTH secretagogues, we studied the effect of passive immunization against CRF or arginine vasopressin (AVP) on plasma ACTH response after hypoglycemia. Passive immunization against AVP decreased significantly hypoglycemia-stimulated ACTH secretion in both 8- and 20-day-old rats, while no change of plasma ACTH response to insulin injection was observed after passive immunization against CRF. This results suggest that CRF does not seem to be involved in the regulation of ACTH secretion after hypoglycemia in the young rat while AVP seems to be the main hypothalamic stimulatory factor for anterior pituitary corticotrophs response to hypoglycemia during the postnatal period.(ABSTRACT TRUNCATED AT 400 WORDS)

Adrenal Glands↗
PubMed1992

Effect of chronic active immunization with antiarginine vasopressin on pituitary-adrenal function in sheep.

ACTH and cortisol diurnal variations and responses to two types of stress (insulin-induced hypoglycemia and isolation-restraint stress) and to an acute injection of CRF were determined in intact as well as in actively antiarginine vasopressin (AVP)-immunized rams. All immunized sheep developed antibodies to AVP, displayed diabetes insipidus, and looked healthy in spite of their lower gain weight. Basal secretion and diurnal variations of ACTH and cortisol were unaltered in the group of anti-AVP-immunized animals. In contrast, ACTH and cortisol responses to both types of stress and CRF injection were significantly reduced compared to those in controls. These results suggest that endogenous AVP plays a physiological role in the corticotropic response to stress. However, endogenous AVP does not appear to affect basal secretion and diurnal variations of ACTH and cortisol.

Adrenocorticotropic Hormone↗
PubMed1992

Ontogeny of insulin-induced hypoglycemia stimulation of adrenocorticotropin secretion in the rat: role of catecholamines.

We previously reported that insulin-induced hypoglycemia (IIH) induces a large increase in plasma ACTH and corticosterone levels in the developing rat during the stress hyporesponsive period and that this effect is mediated, at least partially, by arginine vasopressin (AVP), but not corticotropin-releasing factor. Nevertheless, ACTH secretion in response to IIH in rats immunoneutralized against AVP was still stimulated, suggesting that other regulatory factors participate in the stimulation of ACTH secretion during IIH. It has been suggested that, in the adult rat, during profound hypoglycemia, epinephrine may act at the pituitary level through beta 2-adrenergic receptors to stimulate ACTH secretion. In this report, we studied the effect of the blockade of beta-adrenergic receptors on the pituitary-adrenal axis response to IIH. Rats (20 or 8 day old) were pretreated with saline or 2.5 mg/kg propranolol (a beta-adrenergic receptors antagonist) and subsequently injected with 3 IU/kg insulin. In 20-day-old rats, insulin injection induced a large increase of plasma ACTH concentrations that were unaffected by propranolol pretreatment. In 8-day-old rats, the IIH-induced increase of plasma ACTH levels was significantly reduced by propranolol pretreatment. Pretreatment of 8-day-old rats with 5 mg/kg CGP 20712A (a selective beta 1-adrenergic receptor antagonist) did not change the plasma ACTH response to insulin injection, while pretreatment with 2.5 mg/kg ICI 118551 (a selective beta 2-adrenergic receptor antagonist) resulted in a significant decrease of the IIH-induced stimulation of ACTH secretion. We next studied the effect of the blockade of circulating AVP and/or beta-adrenergic receptors on the pituitary response to IIH. Pretreatment of 8-day-old rats with antiserum anti-AVP or propranolol was followed by a significant reduction of IIH-induced increase of plasma ACTH concentrations. No additive effect was found after pretreatment with both antiserum anti-AVP and propranolol, suggesting that the stimulatory effect of catecholamines during IIH in 8-day-old rats is mediated through a modulation of hypothalamic AVP secretion.

Adrenergic beta-Antagonists↗
PubMed1992

Effects of metyrapone infusion on corticotropin-releasing factor and arginine vasopressin secretion into the hypophysial portal blood of conscious, unrestrained rams.

The effects of rapid changes of circulating cortisol levels on ACTH secretion and on corticotropin-releasing factor (CRF) and arginine vasopressin (AVP) concentrations into hypophysial portal blood were studied in six adult rams. Pharmacological adrenalectomy was obtained by 3 h metyrapone infusion (100 mg.kg-1.h-1). Blockade of cortisol synthesis induced a tenfold increase of plasma ACTH levels accompanied by a moderate increase of CRF secretion (150% vs preinjection levels) and a large increment of AVP secretion (535% vs preinjection levels). ACTH levels remained high during the 3 h following the end of metyrapone infusion. During the same period, CRF secretion was still elevated (231% vs preinjection levels), while AVP secretion was further stimulated (2,151% vs preinjection levels). Subsequent hydrocortisone infusion (66 micrograms.kg-1.h-1) for 2 h induced a rapid decrease of both ACTH and AVP secretion, while CRF levels in hypophysial portal blood still remained elevated. These data suggest that changes in ACTH secretion induced by acute modifications of the negative glucocorticoid feedback are, in addition to the well documented direct effect of cortisol on the corticotropes, mainly mediated by variations of hypothalamic AVP secretion.

Animals↗
PubMed1991

Striatal proenkephalin turnover and gene transcription are regulated by cyclic AMP and protein kinase C-related pathways.

Preproenkephalin metabolism, in the rat, was studied in primary striatal neurons maintained in a chemically defined medium. Acute treatment (30 min) with forskolin (10(-5) M) or phorbol 12 myristate 13 acetate (10(-7) M) resulted, respectively, in a two- and seven-fold increase in methionine-enkephalin secretion. Chronic treatment with forskolin or phorbol 12 myristate 13 acetate (24 h) induced a 100% increase in methionine-enkephalin content (forskolin) and on the other hand a 50% decrease in methionine-enkephalin (phorbol 12 myristate 13 acetate). Both treatments increased preproenkephalin mRNA levels in a time-dependent manner, this augmentation being observable after 180 min by Northern blot analysis and in situ hybridization. These data indicate that under chronic stimulation, with either forskolin or phorbol 12 myristate 13 acetate, proenkephalin turnover is accelerated. However, after stimulation with phorbol 12 myristate 13 acetate, the more potent methionine-enkephalin secretagogue, increased peptide synthesis is not sufficient to replenish methionine-enkephalin intracellular stores. Preproenkephalin gene transcription was analysed by introducing the preproenkephalin gene promoter fused to the bacterial acetyl chloramphenicol transferase reporter gene into primary neurons. Chronic stimulation (48 h) by forskolin (10(-5) M) or phorbol 12 myristate 13 acetate (10(-7) M) of striatal neurons transfected with this fusion gene increased chloramphenicol acetyltransferase activity six-fold and the two effects were additive. These data suggest that the cyclic AMP and the protein kinase C pathways directly activate preproenkephalin gene transcription.

Animals↗
PubMed1990

Interleukins, signal transduction, and the immune system-mediated stress response.

Overwhelming evidence indicates that the administration of cytokines such as IL-1 alpha and beta, IL-6, and TNF-1 alpha stimulates one or more components of the HPA axis. The hypothesis driving this research is that host infection and tissue injury trigger the synthesis and release of several cytokines that act locally at sites of trauma and distally upon entering the circulation. Available evidence suggests that the primary source of HPA axis-acting or circulating cytokines is activated monocytes or macrophages; therefore, a direct relationship should exist between the appearance of monokines in plasma and the subsequent appearance of pituitary-adrenocortical hormones in plasma as well. Clarification of the physiological role of monokines as mediators of the host stress response will come from in vivo studies in which the type, sequence of appearance, duration of elevation, and quantification of each monokine is monitored along with ACTH and glucocorticoids, following an appropriate immune challenge. In several recent reports, investigators have administered bacterial-derived endotoxin or LPS to stimulate the physiological events associated with infection or injury and chronicled plasma levels of IL-1, IL-6, and TNF-alpha (37,56,57). In human subjects, endotoxin challenge enhanced plasma TNF-alpha levels by 1 hour, which returned to basal levels by 4 hours (37), whereas, IL-6 plasma activity increased at 2 hours post-challenge and returned to baseline by 6 hours (56). Thus, both of these monokines are implicated as possible acute activators of the HPA axis. In perhaps the most revealing study to date, LPS challenge of mice indicated both a differential appearance and disappearance rate in serum for TNF-alpha and IL-1 and a differential regulation of these monokines by glucocorticoid feedback (57). Serum TNF was detected 45 minutes post-LPS, peaked by 1 hour, and returned to control levels by 3 hours. Serum corticosterone concentrations rose rapidly over a time course similar to that of TNF. Even after serum TNF concentration had returned to basal conditions, corticosterone levels remained maximally elevated, and serum corticosterone was still significantly above basal levels 24-hour post-LPS. The rapid return of circulating TNF to pre-LPS challenge levels appeared to be regulated by negative glucocorticoid feedback, because TNF remained maximally elevated for at least 6 hours in adrenalectomized or hypophysectomized mice. LPS-induced levels of IL-1 were delayed as compared to serum TNF, peaked at 4 hours, and remained elevated even at 24 hours.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1990

Epinephrine in rat hypophysial portal blood is derived mainly from the adrenal medulla.

This study was performed to determine if epinephrine (EPI) present in hypophysial portal blood has a peripheral or a central origin. Pituitary stalk and femoral arterial EPI plasma levels were simultaneously measured in rats anesthetized with thiopental or urethane. EPI was measured by two different methods: radioenzymatic assay or HPLC followed by electrochemical detection. In thiopental-anesthetized rats, levels were higher in hypophysial portal than in femoral arterial plasma with both methods. In urethane-anesthetized rats, no difference in EPI concentrations was found between peripheral and portal plasma. A rapid blood volume depletion (15 ml/kg in 3 min) evoked a marked elevation of pituitary stalk and arterial EPI plasma concentration while norepinephrine (NE) and dopamine (DA) levels were unaffected. Under both types of anesthesia, the increase of EPI levels was higher in peripheral than in portal plasma. After removal of the adrenal glands, EPI was undetectable or barely detectable in pituitary stalk and arterial plasma. The hemorrhage-induced stimulation of EPI secretion was blunted in portal and peripheral plasma of adrenalectomized rats. These findings indicate that: (1) hypophysial portal EPI plasma concentration is highly dependent on an adrenal source; (2) hypothalamic EPI is not released into portal circulation in response to acute hemorrhage, and (3) anesthesia markedly influences catecholamines plasma levels.

Adrenal Medulla↗
PubMed1990

Insulin-induced hypoglycemia stimulates corticotropin-releasing factor and arginine vasopressin secretion into hypophysial portal blood of conscious, unrestrained rams.

Insulin-induced hypoglycemia (IIH) is a strong stimulator of pituitary ACTH secretion. The mechanisms by which IIH activates the corticotrophs are still controversial. Indeed, in rats the variations of corticotropin-releasing factor (CRF) and arginine vasopressin (AVP) secretion in hypophysial portal blood (HPB) during IIH have been diversely appreciated. This may be due to the stressful conditions required for portal blood collection in rats. We studied the effects of IIH on the secretion of CRF and AVP in HPB and on the release of ACTH and cortisol in peripheral plasma in conscious, unrestrained, castrated rams. After the injection of a low (0.2 IU/kg) or high dose (2 IU/kg) of insulin, ACTH and cortisol levels in peripheral plasma increased in a dose-related manner. After injection of the low dose of insulin, CRF and AVP secretion in HPB were equally stimulated. After injection of the high dose of insulin, CRF secretion was further stimulated, while AVP release was dramatically increased. These results suggest that when the hypoglycemia is moderate, CRF is the main factor triggering ACTH release, and that the increased AVP secretion potentiates the stimulatory effect of CRF. When hypoglycemia is deeper, AVP secretion becomes predominant and may by itself stimulate ACTH release.

Adrenocorticotropic Hormone↗
PubMed1990

Expression and localization of growth hormone-releasing hormone messenger ribonucleic acid in rat placenta: in vitro secretion and regulation of its peptide product.

The placenta is the source of many hypothalamic peptides. We now report that GH-releasing hormone (GHRH) mRNA was detectable in rat placenta. On Northern blot hybridization analysis, the size of the placental GHRH transcript was the same with the putative GHRH precursor mRNA. On in situ hybridization, the cells expressing the GHRH mRNA had the morphological characteristics of cytotrophoblasts. In addition, immunoreactive (IR) postranslational products of GHRH were present in rat placental extracts and in the effluent of in vitro perifused placentae. On gel filtration chromatography, the bulk of IR-GHRH present in placental extracts and perifusion effluent had the same size as the authentic hypothalamic GHRH (5.2K). A higher mol wt form of IR-GHRH of about 10K was also present and may represent the pro-GHRH predicted from the sequence of the GHRH cDNA. The mean basal release of IR-GHRH in the perifusion effluent from full thickness rat placental fragments was 337.3 +/- 38.5 (+/- SE; n = 48) pg/10 min fraction.g tissue. Depolarization by 56 mM KCl increased the concentration of the secreted immunoreactive peptide to 632.2 +/- 50.5. A 10-min exposure to 8-bromo-cAMP caused an immediate, monophasic, and dose-dependent increase in IR-GHRH secretion, which lasted between 20-30 min. The ensuing response to a KCl pulse was similar in size and pattern to that in the control channels. In contrast, a 10-min pulse of phorbol 12-myristate 13-acetate (a protein kinase-C-irreversible activator) induced a gradual, prolonged, and dose-dependent increase in basal GHRH secretion which lasted for at least 4 h. Additionally, phorbol 12-myristate 13-acetate enhanced KCl-induced GHRH secretion. In conclusion, our data suggest that the GHRH gene is expressed in the rat placenta. The placental GHRH transcript and its peptide products appear to have the same size as their hypothalamic counterparts, while the site of its placental GHRH synthesis is the cytotrophoblast. Finally, the secretion of placental GHRH seems to be regulated by both the adenyl cyclase and the protein kinase-C pathways.

Animals↗
PubMed1990

Glucocorticoids regulate peptidyl-glycine alpha-amidating monooxygenase gene expression in the rat hypothalamic paraventricular nucleus.

Peptidyl-glycine alpha-amidating monooxygenase (PAM) is a posttranslational processing enzyme which catalyzes the formation of biologically active alpha-amidated peptides. The two major neuropeptides involved in the regulation of ACTH secretion [CRF and arginine vasopressin (AVP)], synthesized in the parvocellular part of the hypothalamic paraventricular nucleus (PVN), are amidated, and their synthesis and/or release is negatively regulated by glucocorticoids. In this study, using in situ hybridization, we have shown that PAM mRNA is abundantly expressed in the hypothalamic paraventricular and supraoptic nucleus. Surgical adrenalectomy (ADX) induced increases in PAM, CRF, and AVP mRNA in the parvocellular part of the PVN, while corticosterone treatment normalized these values. PAM and AVP gene expression were not changed in the magnocellular part of the PVN or in the supraoptic nucleus. These observations suggest that in addition to stimulation of CRF and AVP synthesis, ADX induces an increase in PAM synthesis in the PVN and, thus, support the hypothesis of increased secretion of both CRF and AVP after ADX.

Adrenalectomy↗
PubMed1989

In vitro-perifused rat testes secrete beta-endorphin and dynorphin: their effect on testosterone secretion.

Leydig cells of many species synthesize and secrete opioid peptides, but the Sertoli and possibly the peritubular cells are the only intratesticular cells having opiate receptors. It is known that Sertoli and peritubular cells can modify the secretion of testosterone from Leydig cells. To test the hypothesis that testicular opioid peptides participate in a Leydig-Sertoli-peritubular-Leydig cell feedback loop that can regulate the intratesticular concentration of testosterone, we have developed a method for the in vitro perifusion of rat testicular fragments in which the intratesticular structure and thus the paracrine feedback loop remains intact. Our data show that both immunoreactive (IR)-beta-endorphin and IR-dynorphin were present in the testicular perifusion effluent; gel chromatography of pooled perifusion effluent show that the bulk of the secreted IR-beta-endorphin had the apparent mol. wt. of synthetic rat beta-endorphin whereas most of the secreted IR-dynorphin was composed of smaller than 4000 mol. wt. forms. On the other hand, the bulk of IR-dynorphin present in rat testicular tissue homogenates eluted in two higher mol. wt. peaks. The effect of mu and kappa opioid agonists and naloxone (a universal opioid antagonist) on both basal and gonadotropin-stimulated testosterone secretion from perifused testicular fragments was then examined; no stimulatory or inhibitory effect of the opioid receptor agonists or naloxone was found on basal and gonadotropin-stimulated testosterone secretion. Parallel experiments with Leydig cells in culture gave similar results.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Chromogranin A messenger RNA expression in the rat anterior pituitary is permissively regulated by the adrenal gland.

The influence of the adrenal gland on the expression of chromogranin A in the anterior pituitary was studied in the rat. Adrenalectomy caused a progressive and pronounced (20% of control levels at day 10 after adrenalectomy) decrease of Chromogranin A mRNA levels in anterior pituitary. Daily injection of dexamethasone (15 micrograms/animal, s.c.) fully reversed the postadrenalectomy decrement in chromogranin A mRNA levels. Chromogranin A protein content, however, was unchanged 10 days after adrenalectomy. In contrast, pro-opiomelanocortin mRNA levels were significantly elevated after adrenalectomy and restored to normal by dexamethasone, with a time course similar to the changes in chromogranin A mRNA levels. These data demonstrate that the adrenal gland permissively regulates chromogranin A expression in the anterior pituitary, at a pretranslational locus, and that this regulation is probably mediated by glucocorticoids.

Adrenal Glands↗
PubMed1989

Corticotropin-releasing factor secretion increases in rat hypophysial portal blood during insulin-induced hypoglycemia.

To study the possible involvement of hypothalamic corticotropin-releasing factor (CRF) in the stimulation of adrenocorticotropic hormone (ACTH) release caused by insulin-induced hypoglycemia (IIH), we measured CRF secretion in hypophysial portal blood (HPB) in rats anesthetized with sodium thiopental after injection of insulin. Before treatment, systemic ACTH levels (952 +/- SE 143 pg/ml; n = 12) were well above normal values, probably reflecting the anesthetic and surgical stress consecutive to the preparation for portal blood collection. Insulin injection induced a significant increase of ACTH release within 15 min (1,588 +/- 168 vs. 741 +/- 144 pg/ml; n = 6, in vehicle-injected rats) which lasted for at least 1 h. CRF levels in HPB were 857 +/- SE 168 pg/ml (n = 13) during the first-hour pretreatment collection. Vehicle injection did not modify CRF secretion (759 +/- 142 pg/ml; n = 6). Insulin injection provoked a significant increase in CRF release (1,449 +/- 257 pg/ml; n = 7). These data suggest that an increased hypothalamic CRF secretion is responsible for the stimulation of pituitary ACTH release following IIH. The possible involvement of central neuromediators in the IIH-induced CRF production is discussed.

Adrenocorticotropic Hormone↗