Biomedical subjects

V Coiro

Publications and source records attributed to V Coiro.

At least 127 records · Page 7Linked to original sources

PubMed1991

Naloxone increases the angiotensin II stimulated rise of arginine vasopressin and oxytocin secretion in man.

The effect of systemic angiotensin II (ANG II) administration on the posterior pituitary function was investigated in normal men. In addition, the role of endogenous opioids in the control of arginine vasopressin (AVP) and/or oxytocin (OT) responses to ANG II was evaluated with the administration of the opioid antagonist naloxone. ANG II (i.v. infusion for 60 min of successively increasing doses of 4, 8 and 16 ng/kg min; each dose for 20 min) was given to 7 normal men, alone or together with naloxone (10 or 20 mg injected i.v. just before ANG II infusion). In all subjects, control experiments with naloxone (10 or 20 mg) alone were also performed. ANG II induced a significant increase in plasma concentrations of AVP and OT. The AVP and OT responses to ANG II had a similar magnitude and followed a similar pattern. The mean peak levels of both hormones were reached at 60 min after the beginning of ANG II infusion. The administration of 10 or 20 mg naloxone alone did not modify the circulating concentrations of AVP and OT. The pretreatment with naloxone significantly increased both ANG II-induced AVP and OT increases twofold, without changing the time course and the secretory pattern of the hormonal responses. These data demonstrate that systemic administration of ANG II in man induces similar simultaneous increments in plasma levels of both AVP and OT. Furthermore, these data suggest the involvement of a naloxone-sensitive opioid mechanism in the regulation of both AVP and OT responses to ANG II in man.

Adult↗

PubMed1991

Relationship between plasma profiles of oxytocin and adrenocorticotropic hormone during suckling or breast stimulation in women.

Oxytocin (OT) administration has been shown to inhibit adrenocorticotropic hormone (ACTH)/cortisol secretion in several experimental conditions. In the present study, the plasma OT responses to suckling in 7 lactating women or to mechanical breast stimulation in 6 normally menstruating women (experimental tests) or to sham stimuli in the same subjects (control tests) were measured and correlated with the simultaneous changes in plasma ACTH/cortisol levels. All women showed similar basal levels of OT, ACTH and cortisol, which remained unmodified after sham stimulation. In contrast, both suckling and breast stimulation produced a significant increase in plasma OT levels and a significant decrease in plasma ACTH concentrations. When OT and ACTH data were considered together, a significant negative correlation was found between the OT increase and the simultaneous ACTH decline. Plasma cortisol levels were lower during suckling or breast stimulation than in control conditions. These data show an inverse relationship between plasma OT and ACTH levels during suckling and breast stimulation in humans, suggesting an inhibitory influence of OT on ACTH/cortisol secretion in a physiological condition.

Adrenocorticotropic Hormone↗

PubMed1991

Different effects of the GABAergic agent sodium valproate on the oxytocin responses to angiotensin II and insulin-induced hypoglycemia in normal men.

The present study was performed in order to establish whether angiotensin II (ANG II) and/or insulin-induced hypoglycemia exert their oxytocin (OT)-releasing effects by interacting with a GABAergic pathway. For this purpose, in 14 normal men the OT responses to ANG II (infusion for 60 min of successively increasing doses of 4, 8 and 16 ng/kg.min, each dose for 20 min; n = 7) or to insulin (0.15 IU/kg)-induced hypoglycemia (n = 7) were evaluated with or without previous treatment with the GABAergic agonist sodium valproate (600 mg in 3 divided doses, p.o.). In all subjects insulin produced a similar hypoglycemic response regardless of sodium valproate administration. Both ANG II and insulin-induced hypoglycemia produced significant increases in plasma OT levels (mean peaks were about 60% higher than baseline). The pretreatment with sodium valproate was unable to change the OT response to hypoglycemia, whereas it abolished the ANG-II-induced OT rise. These data suggest that in man a GABAergic mechanism is involved in the regulation of the OT response to ANG II, but not in the mediation of poglycemia-induced OT release.

Adult↗

PubMed1991

Restoration of normal gonadotropin responses to naloxone by chronic bromocriptine treatment in elderly men.

Naloxone is unable to stimulate FSH and LH secretion in elderly men, suggesting a reduced endogenous opioid control of gonadotropin secretion in senescence. In the present study, we examined whether in elderly men a chronic dopaminergic stimulation with bromocriptine (5 mg/day for 7 days) modifies the gonadotropin response to naloxone (4 mg as an i.v. bolus plus 10 mg infused in 2 h). Eleven younger men (group 1, 22-40 years old) participated as controls. Twenty-two elderly men were selected from a larger population and were divided into two groups: subjects with compensated gonadal failure (normal blood testosterone and elevated gonadotropin concentrations; group 2, n = 11; 62-80 years old) and men with normal gonadal function (normal blood testosterone and gonadotropin levels; group 3, n = 11; 61-82 years old). Naloxone induced a striking LH and a slight but significant FSH increase in group 1, but was unable to change serum gonadotropin concentrations in elderly subjects of both groups 2 and 3. When experiments were repeated after bromocriptine treatment, no significant differences in LH and FSH responses to naloxone were observed in the younger subjects. On the other hand, bromocriptine restored significant gonadotropin responses to naloxone in elderly men. In fact, after bromocriptine, naloxone-induced FSH and LH increments in groups 2 and 3 were indistinguishable from those observed in group 1. These data suggest that in men age-related dopaminergic alterations may underlie the defective endogenous opioid control of gonadotropin secretion.

Adult↗

PubMed1991

Failure of the gamma-aminobutyric acid (GABA) derivative, baclofen, to stimulate growth hormone secretion in Parkinson's disease.

In order to evaluate whether the stimulating effect of GABA on growth hormone (GH) secretion changes in patients affected by Parkinson's disease, ten male parkinsonian patients and ten age matched normal controls were tested with the GABA derivative and GABAergic agent Baclofen (10 mg in a single oral administration at 09.00 h) (experimental test). In a different occasion, normal men and parkinsonian patients were tested with a placebo (control test). Basal GH levels were similar in normal controls and parkinsonian patients and remained unmodified during the control test. Plasma GH levels rose three times within 120 min after the administration of baclofen in the normal subjects. In contrast, plasma GH concentrations remained unmodified after baclofen treatment in the parkinsonian patients. In agreement with previous reports in the literature showing alterations of GABAergic neurotransmission in the parkinsonian brain, these data show a reduced GABAergic control of GH secretion in patients with Parkinson's disease.

Aged↗

PubMed1990

Increase by naloxone of arginine vasopressin and oxytocin responses to insulin-induced hypoglycemia in obese men.

The present study was carried out to establish whether the low arginine vasopressin (AVP) and oxytocin (OT) responses to insulin-induced hypoglycemia observed in obese men was due to alteration of the opioid control of posterior pituitary function. For this purpose, the AVP and OT releasing effect of insulin (0.15 IU/kg bw)--induced hypoglycemia was tested in eight normal weight men and in 10 age-matched obese subjects, without and with the previous treatment with the specific opioid receptor antagonist naloxone (3 mg in an iv bolus). In a control study, naloxone was given alone to the same subjects. Obese men showed similar basal glucose, AVP and OT levels, which remained unmodified after treatment with naloxone alone. Insulin induced a similar decrement of blood glucose levels in all subjects, with a nadir at 30 min. Plasma levels of AVP and OT rose strikingly in normal and obese subjects with mean peak responses at 30 min for AVP and at 45 min for OT. However, both AVP and OT responses were significantly lower in obese than in control subjects. Pretreatment with naloxone did not modify the AVP and OT responses to hypoglycemia in normal weight subjects, whereas it significantly enhanced both hormonal responses in obese subjects. In the presence of naloxone normal controls and obese subjects showed similar responses of both AVP and OT to hypoglycemia. These data indicate that an abnormal activity of endogenous opioids might account for the hypothalamic posterior pituitary dysfunction, which is responsible for the low AVP and OT responses to insulin-induced hypoglycemia in obesity.

Adult↗

PubMed1990

Reduced sensitivity to pirenzepine-induced blockade of growth hormone responses to arginine, exercise, and growth hormone-releasing hormone in type I diabetic subjects.

The present study was performed to establish whether the mechanism by which the cholinergic system influences growth hormone (GH) release was altered in type I diabetic patients. Therefore, we investigated in a dose-response fashion the inhibitory effect of the muscarinic cholinergic receptor antagonist pirenzepine on the GH responses to arginine infusion (30 g infused intravenously (IV) in 30 minutes), exercise (bicycle ergometer test at an intensity of 75 W for 30 minutes), or 1-44 GH-releasing hormone (GHRH) (1 microgram/kg in an IV bolus). In a preliminary study, IV injection of 17.5 mg pirenzepine failed to produce modification in the GH response to arginine infusion in both diabetic (N = 4) and normal subjects (N = 4), and to exercise (diabetics, N = 4; normals, N = 4). Therefore, other subjects were tested without and with 20, 25, and 30 mg pirenzepine during arginine (diabetics, N = 7; normals, N = 7) or exercise (diabetics, N = 7; normals, N = 7) tests. Each subject was tested four times. Diabetic patients presented higher GH responses to stimulation with arginine or exercise than normal controls. In both groups, pirenzepine administered at doses ranging from 20 to 30 mg produced a dose-related inhibition of the GH response to arginine and exercise, which was almost complete when 30 mg pirenzepine was administered. However, the percent inhibition produced by 20 or 25 mg pirenzepine in the arginine test and by 20 mg in the exercise test was significantly lower in the diabetic patients than in the normal controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗

PubMed1990

Effect of obesity and weight loss on arginine vasopressin response to metoclopramide and nicotine from cigarette smoking.

We have previously reported an impaired arginine vasopressin (AVP) response to insulin-induced hypoglycemia in obese men, suggesting a hypothalamic-posterior pituitary disorder in obesity. In the present study, we examined the AVP response to other releasing stimuli with a central site of action. The AVP response of 10 obese men to metoclopramide (MCP) or nicotine inhaled with cigarette smoking was compared with that obtained in eight sex- and age-matched controls. The AVP increase during nicotine and MCP tests were significantly lower in the obese patients than in the normal controls. Obese men were restudied after substantial weight loss. The AVP response to nicotine and MCP administration was significantly higher than before slimming and did not differ from that observed in the normal weight subjects. These results demonstrate obesity-related alterations in the AVP responsiveness to nicotine inhaled with cigarette smoking and MCP, supporting the hypothesis for a hypothalamic-posterior pituitary disorder in obesity.

Adult↗

PubMed1990

Luteinizing hormone and cortisol responses to naloxone in normal weight women with bulimia.

The present study was undertaken in order to establish whether alterations in the endogenous opioid control of luteinizing hormone (LH) and ACTH/cortisol secretion occur in bulimic women with normal body weight and normal menstrual cycles. For this purpose, the capability of the opioid antagonist naloxone (4 mg injected as an intravenous bolus at time 0, plus 10 mg infused over 2 hr) to increase the circulating levels of LH and cortisol was tested in nine bulimic women and in nine age- and weight-matched normal controls. All women were tested on the 22nd day of a normal menstrual cycle. Two days later, a control test with normal saline (NaCl 0.9%) instead of naloxone was performed. The basal levels of LH and cortisol were similar in the bulimic and normal subjects and were not modified by the administration of normal saline. In contrast, the administration of naloxone significantly increased plasma LH and cortisol levels in all subjects, with peak LH responses at 30 min and peak cortisol responses at 60 min. The naloxone-induced LH and cortisol increases were significantly higher in the bulimic women than in the normal controls. These data indicate the presence of an increased opioid inhibitory tone in the control of LH and ACTH/cortisol secretion in normal weight bulimic women with normal menstrual cycles.

Adult↗

PubMed1990

Serotonergic control of TSH and PRL secretion in obese men.

To evaluate whether the inhibitory control of TSH and the stimulatory control of prolactin (PRL) secretion exerted by endogenous serotonin was altered in obesity, 22 obese men and 10 normal controls were tested with TRH (200 micrograms IV bolus) in the presence (experimental test) and absence (control test) of the serotonergic agonist fenfluramine (60 mg PO 90 min before TRH). Control and experimental tests were also performed in seven male patients with subclinical hypothyroidism and were repeated in the same obese subjects after substantial weight loss. Basal TSH levels were similar in control and obese men. Normal TSH responses to TRH (peak less than or equal to 14 mU/L) were observed in all normal controls (mean peak +/- SE 9.8 +/- 0.6 mU/L). In contrast, obese men were divided into two groups: nine in whom the TRH-induced TSH rise was higher than normal (group I: mean peak = 16.5 +/- 0.5 mU/L) and 13 in whom it was normal (group II: mean peak = 10.6 +/- 0.7 mU/L). The hypothyroid men all had elevated basal and TRH-stimulated TSH levels. Basal PRL concentrations were similar in the normal controls and both groups of obese subjects. The PRL response to TRH was lower in both group I and group II obese men than in normal controls and was similar between group I and group II.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1990

Growth hormone responses to growth hormone-releasing hormone, clonidine and insulin-induced hypoglycemia in normal weight bulimic women.

The growth hormone (GH) responses to GH-releasing hormone (GHRH; 1 microgram/kg BW in an i.v. bolus), clonidine (150 micrograms in a single oral dose) and insulin (0.15 IU/kg BW in an i.v. bolus) induced hypoglycemia were evaluated in 7 normal weight bulimic women with regular menstrual cycles and in 7 age- and weight-matched normal women. In addition, the effect of thyrotropin-releasing hormone (TRH; 200 micrograms in an i.v. bolus) on serum thyroid-stimulating hormone (TSH) and GH levels was measured in the same subjects. Tests were carried out in random order on the 22nd days of the following menstrual cycles. A control test with the i.v. administration of normal saline instead of drugs was carried out 2 days after the TRH test. Basal GH levels were significantly higher in bulimic women than in normal controls; despite higher GH levels, bulimic women showed normal circulating concentrations of somatomedin-C (Sm-C). Serum GH levels remained unmodified during the control test. In contrast, the administration of GHRH, clonidine or insulin induced significant GH responses in all subjects. Bulimic and normal women showed comparable responses after GHRH, clonidine or hypoglycemia. The hypoglycemic response to insulin was similar in bulimic and control subjects. The administration of TRH was unable to increase the circulating levels of GH in the normal controls, whereas it significantly increased GH concentrations in 5 of 7 bulimic women.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1990

Inhibitory effect of ethanol on the arginine vasopressin response to insulin-induced hypoglycemia and the role of endogenous opioids.

The present study was undertaken in order to establish whether ethanol is able to modify the arginine vasopressin (AVP) response to insulin-induced hypoglycemia in man. In addition, the possible involvement of opioid peptides in the mediation of hypoglycemia and/or ethanol action was investigated. For these purposes, the AVP response to an intravenous (0.15 U/kg) insulin tolerance test (ITT) was measured in 6 normal men treated with saline, naloxone (2 or 4 mg as intravenous bolus plus 5 or 10 mg infused over 105 min), ethanol (50/110 ml of whiskey p.o.), or the combination of ethanol and naloxone. Plasma AVP levels rose by about three-fold during insulin-induced hypoglycemia; administration of naloxone did not modify, whereas ethanol completely abolished the AVP response during ITT. When ethanol was given together with naloxone, AVP rose by only two-fold in response to hypoglycemia. Neither ethanol nor naloxone modified the basal secretion of AVP as tested during 45 min before the ITT. These data demonstrate that ethanol inhibits the AVP response to hypoglycemia. Naloxone-sensitive endogenous opioids do not seem to be involved in the control of basal and hypoglycemia-induced AVP secretion. In contrast, since naloxone partially reversed the inhibiting effects of ethanol, a partial involvement of opioid peptides in ethanol action may be supposed.

Adult↗

PubMed1990

Abnormal arginine-vasopressin responses to metoclopramide and insulin-induced hypoglycemia in type I diabetes mellitus.

Alterations in the control of arginine-vasopressin (AVP) secretion have been described in type I diabetes mellitus. In order to gain a better insight into this problem, we examined whether insulin-dependent diabetics in good metabolic conditions and without diabetic complications had an abnormal AVP responsiveness to metoclopramide (MCP), an AVP-stimulating agent with a central site of action. In addition, we tested the AVP response to insulin-induced hypoglycemia in the same subjects. Twenty insulin-dependent diabetic men without neuropathy or other diabetic complications were divided into two groups according to the duration of their illness (10 patients who had been diabetic for less than 10 years, group 1, and 10 patients who had been diabetic for more than 10 years, group 2). Eleven age- and weight-matched normal men participated as controls. All groups were tested with MCP (20 mg in an intravenous bolus) and, on a different occasion, with insulin-induced (0.15 IU/kg) hypoglycemia. Experiments started after optimization of the metabolic status of the diabetic men by 3 days of treatment with continuous subcutaneous insulin infusion. Basal concentrations of AVP were similar in all groups (diabetics of group 1: 2.2 +/- 0.2 pmol/l, mean +/- SE; group 2: 2.3 +/- 0.2 pmol/l; normal controls: 2.2 +/- 0.2 pmol/l). Administration of MCP induced a striking elevation of plasma AVP levels in the normal controls and in the diabetic subjects of groups 1 and 2. All subjects showed a mean peak response at 15 min.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1990

5-HT1-, but not 5-HT2-serotonergic, M1-, M2-muscarinic cholinergic or dopaminergic receptors mediate the ACTH/cortisol response to metoclopramide in man.

The possible mediation of dopaminergic, muscarinic cholinergic and/or serotonergic receptors in the response of ACTH/cortisol to metoclopramide (MCP) was evaluated in 27 normal men. All subjects were tested with MCP (10 mg in an intravenous bolus plus placebo or saline, NaCl 0.9%, control test). For the other tests (experimental tests), the men were divided into three groups of 9 subjects each. One group was tested with MCP in the presence of the dopaminergic agonist bromocriptine (5 mg p.o. 3 h before MCP), another group was tested with MCP plus the M1- and M2-muscarinic-cholinergic antagonist atropine (1.2 mg in an intravenous bolus, just before MCP) or the M1-muscarinic receptor blocker pirenzepine (40 mg in an intravenous bolus 10 min before MCP). The third group was tested with MCP after treatment with the selective 5-HT1-serotonergic receptor blocker metergoline (10 mg/day p.o. in 5 divided doses for 4 days before MCP) or the 5-HT2-serotonergic receptor antagonist ketanserin (10 mg as a slow 3-min intravenous injection, 5 min before MCP). ACTH and cortisol rose by 45 and 55%, respectively, in response to MCP. The basal levels of ACTH and cortisol were not modified by bromocriptine, atropine, pirenzepine, metergoline or ketanserin treatment. Both ACTH and cortisol responses to MCP did not change significantly after bromocriptine, atropine, pirenzepine or ketanserin administration, whereas they were completely abolished by pretreatment with metergoline. Additional experiments were performed in order to evaluate whether the effect of metergoline on the ACTH/cortisol response to MCP depends on the amount of the serotonergic antagonist (dose-response study).(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenocorticotropic Hormone↗

PubMed1990

Inhibition by dexamethasone of arginine vasopressin and ACTH responses to insulin-induced hypoglycemia and cigarette smoking in normal men.

Glucocorticoids are known to inhibit the AVP response to osmotic and hemodynamic stimuli in humans. In the present study, we examined whether the AVP response to other primary stimuli, such as insulin-induced hypoglycemia and cigarette smoking was sensitive to inhibition by dexamethasone. The plasma ACTH responses were also measured. Twenty-four normal men were randomly divided into 3 groups of 8 subjects. One group was tested with insulin (0.15 IU/kg in an iv bolus) and another group with cigarette smoking (2 non-filter cigarettes smoked in succession within 10 min) with and without pretreatment with dexamethasone (2 or 4 mg in an iv bolus 10 min before insulin or smoking). The third group was tested with dexamethasone alone (2 or 4 mg in an iv bolus). The administration of dexamethasone (2 or 4 mg) alone did not modify the circulating levels of AVP and ACTH at any time during the next hour. The hypoglycemic response to insulin was similar regardless of dexamethasone treatment. AVP rose sharply in response to both hypoglycemia and smoking, reaching mean peak levels at 45 and 30 min, respectively. After both stimuli, the mean peak levels of AVP were 2.25 times higher than baseline. Pretreatment with dexamethasone (2 or 4 mg) significantly decreased the AVP responses to both hypoglycemia and cigarette smoking. Following pretreatment with dexamethasone (2 or 4 mg) the AVP increments in response to hypoglycemia or cigarette smoking were only 1.7 times higher than baseline. The plasma concentrations of ACTH were strikingly increased by hypoglycemia. The mean peak level was 3.5 times higher than baseline and was reached at 45 min.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenocorticotropic Hormone↗

PubMed1989

Inhibition by sodium valproate of the arginine vasopressin and adrenocorticotropin responses to angiotensin II in normal men.

The present study was carried out in order to determine whether angiotensin II (ANG II) exerts its stimulatory effect on plasma concentration of arginine vasopressin (AVP) and adrenocorticotrophic hormone (ACTH) by interacting with a (gamma-aminobutyric acid) GABAergic pathway. For this purpose, the effect of the GABAergic agonist sodium valproate (600 mg in 3 divided doses p.o.) on the ACTH and AVP responses to ANG II (infusion for 60 min of successively increasing doses of 4, 8 and 16 ng/kg min; each dose for 20 min) administration was evaluated in 7 normal men. In all subjects control ANG II tests were performed with a placebo instead of sodium valproate. ANG II induced a significant increase of AVP at 60 min and ACTH at 90 min after the beginning of infusion. The pretreatment with sodium valproate reduced significantly both ANG II-induced AVP and ACTH rises, without changing the time course of the hormonal responses. These data suggest the involvement of a GABAergic mechanism in regulation of both AVP and ACTH responses to ANG II in man.

4-Aminobutyrate Transaminase↗

PubMed1989

The infusion of somatostatin reduces the arginine-vasopressin response to insulin-induced hypoglycemia in man.

The effect of an iv infusion of somatostatin (SRIH) (4.1 micrograms/min x 90 min) on the basal secretion of arginine-vasopressin (AVP) and on the AVP response to insulin (0.15 IU/Kg) - induced hypoglycemia was studied in 6 normal men. Basal AVP secretion was not modified by SRIH administration. The blood glucose decrements induced by insulin were similar in the control insulin-tolerance test (ITT) and in the ITT + SRIH test, whereas the AVP response to hypoglycemia was significantly lower in the presence of SRIH. The mean peak AVP increase was three times higher than the basal value in the control ITT, but only two times during SRIH administration. Infusion of higher doses of SRIH (7 micrograms/min x 90 min) produced similar results. These data suggest the involvement of a somatostatinergic mechanism in regulation of AVP response to hypoglycemia.

Adrenocorticotropic Hormone↗

PubMed1989

Naloxone abolishes the inhibiting effect of somatostatin on the release of oxytocin evoked by insulin-induced hypoglycemia in humans.

The effect of somatostatin (SRIH) on the release of oxytocin (OT) in response to hypoglycemia during insulin tolerance test (ITT) was studied in seven normal men. Subjects were injected intravenously with 0.15 U/kg insulin alone (control test) or together with SRIH (4.1 micrograms/min x 90 min), naloxone (10 mg in an IV bolus), or the combination of the two substances. Plasma OT concentrations rose significantly during ITT; the OT response was significantly reduced by the treatment with SRIH and increased in the presence of naloxone. When both SRIH and naloxone were given, the OT response to hypoglycemia did not differ from that observed in the control test. These findings provide evidence that the effect of hypoglycemia on plasma OT levels is sensitive to the inhibition by SRIH and by naloxone-sensitive endogenous opioids. Because naloxone reversed the inhibiting effects of SRIH, an involvement of opioid peptides in SRIH action might be supposed. Alternatively, SRIH and naloxone-sensitive opioids might produce their inhibiting effects on OT rise in response to hypoglycemia through independent pathways.

Adult↗