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Biomedical subjects

G Lembo

Publications and source records attributed to G Lembo.

At least 19 recordsLinked to original sources
PubMed2004

Phosphoinositide 3-kinase gamma: kinase-dependent and -independent activities in cardiovascular function and disease.

Cardiac function is controlled by GPCRs (G-protein-coupled receptors) which exert their function by triggering numerous signalling pathways, including the activation of PI3K (phosphoinositide 3-kinase). The GPCR-activated PI3Kgamma is weakly expressed in the heart, but the deletion of its expression in mice causes remarkable phenotypes. Indeed, the lack of PI3Kgamma does not modify heart rate and blood pressure, but does increase contractility, particularly in response to stimuli that enhance cardiac contractile force, such as catecholamines. Consistently, treatment of mutant cardiomyocytes with beta-adrenergic agonists causes an abnormal increase in the elevation of cAMP production. On the other hand, PI3Kgamma appears to play a role in mediating the contractile depression exerted by other GPCR agonists, such as PAF (platelet-activating factor), that are released in pathological conditions, such as after an ischaemic insult. The receptor for PAF coupled to G(i) activates PI3Kgamma, which, in turn, is essential to promote Akt phosphorylation, NOSIII (nitric oxide synthase isoform III) activation and the production of nitric oxide, a well characterized cardiodepressing agent. As a whole, PI3Kgamma appears to negatively control cardiac contractility through different signalling mechanisms, thus becoming a possible drug target for the treatment of critical human cardiac pathologies, such as infarction or heart failure.

Animals↗
PubMed2001

Impaired insulin-like growth factor I vasorelaxant effects in hypertension.

Insulin-like growth factor I (IGF-I) can be considered a factor potentially involved in arterial hypertension not only for its growth-promoting features but also for its effects on vascular tone. Nevertheless, the actions of the hormone on vascular reactivity are still unexplored in hypertension. Therefore, the vasodilation induced by increasing doses of IGF-I and the modulation of norepinephrine vasoconstriction induced by low levels of the hormone were tested on aortic rings of spontaneously hypertensive and normotensive rats. The results indicate that the vasodilation evoked by IGF-I is impaired in hypertensive rats (Delta% of maximal vasorelaxation, 30+/-1 versus 41+/-1; P<0.01), and after the removal of endothelium or the inhibition of endothelial NO synthase, the vasodilation evoked by the hormone was blunted in both rat strains and became similar between hypertensive and normotensive rats (Delta% of maximal vasorelaxation, 21+/-1 versus 20+/-1; P=NS). Moreover, IGF-I does not show any effect on norepinephrine vasoconstriction in hypertensive rats, and this alteration may depend on the lack of sensitizing effect exerted by IGF-I on alpha(2)-adrenergic-evoked NO vasorelaxation. The defect in IGF-I vascular action is also present in young spontaneously hypertensive rats (age 5 weeks). In conclusion, our data demonstrate that IGF-I vasorelaxant properties are impaired in spontaneously hypertensive rats, suggesting that such defect may play a causative or permissive role in the development of hypertensive conditions.

Animals↗
PubMed2001

A common variant of endothelial nitric oxide synthase (Glu298Asp) is an independent risk factor for carotid atherosclerosis.

BACKGROUND AND PURPOSE: Endothelium-derived NO is formed from L-arginine by endothelial NO synthase (eNOS) encoded by the NOS 3 gene on chromosome 7. Because several studies have indicated that NO plays a key role in the development of the atherosclerotic process, we investigated whether common variants in the eNOS gene are associated with an increased risk of plaque on carotid arteries. METHODS: We studied 375 subjects attending the hypertension center of our institution to be screened for arterial hypertension. The examined subjects were classified according to the presence of carotid plaques (intima-media thickness >/=1.5 mm), and 2 intronic (CA and 27-bp repeats) polymorphisms and 1 exonic (Glu298Asp) polymorphism of the eNOS gene were explored. RESULTS: Only the Glu298Asp polymorphism of eNOS was associated with the presence of carotid plaques (P:<0.05). In particular, there was an excess of homozygotes for the Asp298 variant among subjects with carotid plaques, whereas the number of subjects who had the Glu298 allele in exon 7 of the eNOS gene was equally distributed in both study groups. Interestingly, the risk of having carotid plaques was increased approximately 3 times in subjects who were homozygotic for the Asp298 variant compared with subjects who were homozygotic for the Glu298 variant and was independent of the other common risk factors (age, blood pressure, and smoking). CONCLUSIONS: Homozygosity for Asp298, a common variant of the eNOS gene, is an independent risk factor for carotid atherosclerosis in this study population.

Adult↗
PubMed2000

Noradrenergic vascular hyper-responsiveness in human hypertension is dependent on oxygen free radical impairment of nitric oxide activity.

BACKGROUND: Noradrenergic vascular hyper-responsiveness is a hallmark of essential hypertension. To evaluate whether nitric oxide plays a role in the enhanced vascular response to norepinephrine in hypertension, we examined 32 hypertensives and 28 normotensives who were distributed in 3 experimental series. METHODS AND RESULTS: In the first series, we measured the forearm blood flow (FBF) response to a norepinephrine infusion under control conditions and during the infusion of L-N-monomethylarginine (L-NMMA). Norepinephrine evoked dose-dependent vasoconstriction that was greater in hypertensives than in normotensives (maximum FBF, -61+/-1 versus -51+/-1%; P<0.01). During L-NMMA infusion, norepinephrine vasoconstriction was not modified in hypertensives; however, it was potentiated in normotensives (maximum FBF, -64+/-2%; P<0.01). In the second series, we tested whether norepinephrine vasoconstriction could be affected by an antioxidant such as ascorbic acid. Norepinephrine vasoconstriction was blunted by ascorbic acid administration only in hypertensives (maximum FBF, -49+/-3 versus -63+/-2%; P<0.01); the vasoconstriction became similar to that observed in normotensives. During ascorbic acid plus L-NMMA administration, the vascular response to norepinephrine increased to a similar extent in both study groups. To rule out the possibility that the effect of ascorbic acid on norepinephrine vasoconstriction could depend on adrenergic receptor-induced nitric oxide release, in the last series we inhibited endogenous nitric oxide and replaced it with an exogenous nitric oxide donor (sodium nitroprusside). Even in these conditions, ascorbic acid attenuated norepinephrine vasoconstriction only in hypertensives (maximum FBF, -50+/-2 versus -62+/-1%; P<0.01). CONCLUSIONS: Our data demonstrate that noradrenergic vascular hyper-responsiveness in hypertension is dependent on an impairment of nitric oxide activity that is realized through norepinephrine-induced oxygen free radical production.

Adult↗
PubMed2000

Lack of effect of insulin on glucose utilization of the hypothalamus in normotensive and hypertensive rats.

Hypertension is frequently associated with insulin resistance and enhanced sympathetic activity supposedly mediated by an effect of the hormone on the hypothalamus. In this study we sought to determine whether insulin modifies the functional activity of the hypothalamus and other brain areas of spontaneously hypertensive (SHR) and normotensive WKY rats. The study was carried out in control and hyperinsulinemic, normoglycemic rats. Insulin plasma levels were increased to 198 +/- 10 (WKY) or 220 +/- 10 microunits/ml (SHR). Brain functional activity was evaluated by the 2-[14C]deoxyglucose method for measuring local rates of glucose utilization. The results show that insulin has no effect on any of the brain areas examined including the hypothalamus, of both WKY and SHR rats. The two strains of rats have comparable cerebral metabolic rates also under basal conditions.

Animals↗
PubMed2000

Insulin-stimulated cardiac glucose uptake is impaired in spontaneously hypertensive rats: role of early steps of insulin signalling.

OBJECTIVE: Although the heart is one of the target organs of insulin, it is still unknown whether the effect of insulin on cardiac muscle is preserved in essential hypertension, where insulin resistance has been observed in skeletal muscle. METHODS: We evaluated cardiac glucose uptake and the early steps of insulin signalling in spontaneously hypertensive (SHR, 10-12 weeks old) and in age-matched normotensive Wistar-Kyoto (WKY) rats. Cardiac glucose uptake (micromol/100 g per min) was assessed by 2-[14C]deoxyglucose method. After an overnight fast, 16 WKY rats and 17 SHR underwent a hyperinsulinemic euglycemic clamp. In particular, 2-h intravenous (i.v.) infusion of insulin (10 mU/kg per min) or saline (NaCl 0.9%) was administered, followed by an i.v. bolus injection of 2-[14C]deoxyglucose (100 microCi/kg) to measure cardiac glucose uptake. RESULTS: During saline infusion, cardiac glucose uptake was significantly higher in SHR compared to WKY rats (85 +/- 18 versus 8 +/- 3 mg/kg per min, P < 0.01). Furthermore, insulin was able to markedly increase cardiac glucose uptake in WKY rats whereas this insulin action was entirely abolished in SHR; thus, the cardiac glucose uptake became similar in the two rat strains (76 +/- 16 versus 82 +/- 16 mg/kg per min, not significant). More importantly, during saline infusion SHR showed a significantly higher phosphorylation of insulin receptor substance-1 (IRS-1) coupled to enhanced association of the p85 subunit of phosphatidylinositol 3-kinase (PI 3-kinase) to IRS-1 and to an increased PI 3-kinase activity compared to WKY rats. As expected, insulin exposure evoked an activation of its signalling cascade in WKY rats. In contrast, in SHR, the hormone failed to activate post-receptor molecular events. CONCLUSIONS: Our data indicate that the heart of SHR shows an overactivity of the proximal steps of insulin signalling which cannot be further increased by the exposure to the hormone. This abnormality may account for the marked increase of basal cardiac glucose uptake and the loss of insulin-stimulated glucose uptake observed in SHR.

Animals↗
PubMed2000

Muscle sympathetic nerve activity in patients with acromegaly.

Muscle sympathetic nerve activity was measured in nine acromegalic patients (age, 35 +/- 4 yr; body mass index, 28 +/- 2 kg/m2) and eight healthy subjects (age, 32 +/- 3 yr; body mass index, 25 +/- 2 kg/m2) by combining the forearm arterial-venous difference technique with the tracer method [infusion of tritiated norepinephrine (NE)]. Muscle NE release was quantified both at rest and during physiological hyperinsulinemia while maintaining euglycemia (approximately 90 mg/dL) by means of the euglycemic clamp. Arterial plasma NE was similar in the two groups at rest (197 +/- 28 and 200 +/- 27 pg/mL (-1) and slightly increased during insulin infusion. Forearm NE release was 2.33 +/- 0.55 ng x liter(-1) x min(-1) in healthy subjects and 2.67 +/- 0.61 ng x liter(-1) x min(-1) in acromegalic subjects in the basal state and increased to a similar extent during insulin infusion in both groups (3.13 +/- 0.71 and 3.32 +/- 0.75 ng x L(-1) x min(-1), P < 0.05 vs. basal), indicating a normal stimulatory effect of insulin on muscle sympathetic activity. In contrast, insulin-stimulated forearm glucose uptake was markedly lower in acromegalic patients (2.3 +/- 0.4 mg x L(-1) x min(-1)) than in control subjects (7.9 +/- 1.3 mg x L(-1) x min(-1), P < 0.001), indicating the presence of severe insulin resistance involving glucose metabolism. Our data demonstrate that patients with long-term acromegaly have normal sympathetic activity in the skeletal muscle in the basal, postabsorptive state and normal increments in NE spillover in response to the sympatho-excitatory effect of insulin. Thus, the presence of severe insulin resistance in acromegaly is not accounted for by adrenergic mechanisms.

Acromegaly↗
PubMed2000

Leptin induces direct vasodilation through distinct endothelial mechanisms.

In this study, we reveal that leptin evokes an acute hypotensive effect in 6-hydroxydopamine sympathectomized rats (response to maximal leptin dose, mean blood pressure: from 92 +/- 4 to 78 +/- 2 mmHg, P < 0.01). This hemodynamic effect is related to a direct action of the hormone on vascular tone, since in aortic and mesenteric rings increasing doses of leptin evoke a dose-dependent vasorelaxation (aorta: from 3 +/- 1 to 36 +/- 3, n = 15; mesenteric: from 6 +/- 1 to 30 +/- 5, n = 10), which is impaired by endothelial denudation. In particular, leptin-evoked vasorelaxation is impaired by nitric oxide synthase inhibition in aorta (delta% of maximal response: from 36 +/- 3 to 3 +/- 1, P < 0.01) and by endothelium-derived hyperpolarizing factor (EDHF) inhibition in mesenteric arteries (delta% of maximal response: from 30 +/- 5 to 7 +/- 2, P < 0.01), suggesting that vasorelaxation evoked by leptin is heterogeneous and related to the vascular bed. Finally, the inhibition of nitric oxide synthase by NG-nitro-L-arginine-methyl ester does not modify blood pressure response to leptin, suggesting a predominant role of the EDHF mechanism in the hypotensive effect of leptin.

Animals↗
PubMed1999

Increased cardiomyocyte apoptosis and changes in proapoptotic and antiapoptotic genes bax and bcl-2 during left ventricular adaptations to chronic pressure overload in the rat.

BACKGROUND: Left ventricular hypertrophy (LVH) represents both an adaptive response to increased cardiac work load and a precursor state of heart failure. Recent evidence linked cardiac myocyte death by apoptosis with LVH and heart failure. It remained unclear, however, whether apoptosis participated in the transition from LVH to left ventricular dysfunction (LVD). METHODS AND RESULTS: Cardiac myocyte apoptotic events and changes in apoptosis-specific genes were studied in a rat model of chronic pressure overload induced by transverse aortic constriction. The changes in left ventricular geometry and function were assessed by echocardiography. Transverse aortic constriction rats progressively developed "concentric" LVH and subsequently, LVD. A similar distribution of LVH and LVD was found 18 weeks after surgery. At this time point, we determined the occurrence of myocyte apoptosis by DNA laddering, in situ DNA TUNEL labeling, and light and electron microscopy. The monitoring of proapoptotic and antiapoptotic genes was determined by Western blot and immunohistochemistry. Our data demonstrated that cardiomyocyte apoptotic events increased from virtually undetectable (in sham-operated controls, SH) to 0.8/10(3) and 1.5/10(3) positive nuclei in LVH and LVD, respectively. Fibrosis also increased in the subendocardial and midwall regions of LVH and LVD rats compared with SH. Expression of the proapoptotic gene bax increased, whereas that of antiapoptotic gene bcl-2 decreased in LVH and LVD compared with SH. CONCLUSIONS: These data suggest that in response to chronic pressure overload, cardiomyocyte-specific apoptosis contributed to the transition from LVH to LVD. LVH and LVD were accompanied by a dramatic cardiomyocyte upregulation of the proapoptotic gene bax and reduced bcl-2/bax ratio, predisposing cardiomyocytes to apoptosis.

Animals↗
PubMed1999

Assignment of human teratocarcinoma derived growth factor (TDGF) sequences to chromosomes 2q37, 3q22, 6p25 and 19q13.1.

The human teratocarcinoma derived growth factor 1 (TDGF1) gene maps on chromosome (Chr) 3p21.3. One pseudogene (TDGF3) maps on Chr Xq21-->q22. We now report the nucleotide sequence and chromosome location of three additional TDGF pseudogenes. The three new sequences (TDGF2, TDGF4 and TDGF5) are truncated at the 5' end and have accumulated several point mutations, deletions and insertions. TDGF2, TDGF4 and TDGF6 map on Chrs 2q37, 6p25 and 3q22, respectively. Finally, Southern blot analysis of DNA from normal individuals shows a highly variable restriction pattern of the TDGF sequences.

Alu Elements↗
PubMed1998

Systemic hypertension and coronary artery disease: the link.

A direct, continuous, and independent association between blood pressure values and incidence of coronary artery disease has been well documented. However, the evidence that the reduction of blood pressure alone is not able to completely reverse the increase in the risk of coronary artery disease associated with essential hypertension suggests that the link between hypertension and coronary artery disease is a complex process including other factors beside the increase in blood pressure values. In this regard, the main determinant of coronary artery disease in hypertensive patients seems to be the development of left ventricular hypertrophy (LVH). In fact, hypertensive patients who died from sudden cardiac death showed a lesser degree of coronary atherosclerosis compared with normotensives, but a higher incidence of LVH. Several mechanisms can account for the increased coronary risk with LVH, including (1) an increase in left ventricular (LV) mass, which by itself requires more oxygen for tissue perfusion; (2) impairment of coronary flow reserve; (3) perivascular fibrosis, which then impairs oxygen supply to the myocardium; and (4) deterioration of LV diastolic function, which hampers myocardial perfusion. Recently, a study reported an impairment of endothelial function and abnormal control of the sympathetic tone in hypertensive patients, which may contribute to the risk of coronary artery disease. In particular, the impaired endothelial function resulting in a prevalence of vasoconstrictive, thrombogenic, and proliferative factors may account for the enhanced ischemic susceptibility of these patients. Furthermore, the cardiac adrenergic system plays an important role in regulating myocardial blood flow. On one hand, hypertensive patients show an exaggerated sympathetic response to physiologic stimuli, whereas on the other hand, the beta-adrenergic receptor-mediated vasodilating component of the sympathetic response is blunted in hypertension. Finally, excess body weight, dyslipidemia, glucose intolerance, and hyperinsulinemia, which are frequently interrelated, represent independent predictors of both coronary artery disease and hypertension.

Animals↗
PubMed1998

Sympathetic deactivation by growth hormone treatment in patients with dilated cardiomyopathy.

AIMS: We examined the effects of growth hormone administration on the sympathetic nervous system in patients with idiopathic dilated cardiomyopathy. BACKGROUND: Growth factor therapy is emerging as a new potential option in the treatment of heart failure. Although growth hormone provides functional benefit in the short term, it is unknown whether it affects the sympathetic nervous system, which plays a role in the progression of heart failure. METHODS: Seven patients with idiopathic cardiomyopathy received 3 months treatment with recombinant human growth hormone (0.15-0.20 IU.kg-1.week-1). Standard medical therapy was unchanged. Myocardial norepinephrine release, both at rest and during submaximal physical exercise, plasma aldosterone, and plasma volume were measured before and after growth hormone treatment. Myocardial norepinephrine release was assessed from arterial and coronary venous plasma concentrations of unlabelled and tritiated norepinephrine and coronary plasma flow (thermodilution). RESULTS: Growth hormone induced a significant fall in myocardial norepinephrine release in response to physical exercise (from 180 +/- 64 to 99 +/- 34 ng.min-1; P < 0.05). Basally, plasma aldosterone was 189 +/- 28 and 311 +/- 48 pg.ml-1 in the supine and upright position, respectively, and fell to 106 +/- 16 (P < 0.01) and 182 +/- 29 pg.ml-1 (P < 0.05) after growth hormone therapy. Growth hormone increased plasma volume from 3115 +/- 493 ml to 3876 +/- 336 ml (P < 0.05), whereas serum sodium and potassium concentrations were unaffected. CONCLUSIONS: The data demonstrate that growth hormone administration to patients with idiopathic cardiomyopathy reduces myocardial sympathetic drive and circulating aldosterone levels. This neurohormonal deactivation may be relevant to the potential, long-term use of growth hormone in the treatment of patients with heart failure.

Adult↗
PubMed1998

Benefits of combination therapy in hypertensive patients with associated coronary artery disease: a subgroup with specific demands.

Although prevention of coronary artery disease (CAD) is one of the main goals of antihypertensive therapy, when first seen hypertensive patients often have associated CAD. These patients need a therapy that can exert an acute anti-ischemic action, such as ad hoc relief of angina pectoris, and can also reduce the incidence of myocardial infarction (MI) or reinfarction. Reduction in blood pressure (BP) alone does not appear to be adequate because in hypertensive patients CAD is a complex and multifactorial process involving not only hemodynamic, neurohormonal, and metabolic factors but also hypertension-induced myocardial and vascular structural changes, which appear independently to contribute to risk for CAD. In theory, antihypertensive combination therapy, by summing the different effects of various drugs, appears to have a greater capacity for comprehensive management of hypertensive patients with CAD. Simultaneous administration of angiotensin-converting enzyme (ACE) inhibitors and calcium-channel blockers appears to be particularly effective. In several clinical trials with long-term follow-up, ACE inhibitor therapy has been associated with a substantial reduction in the risk for major ischemic events. The antiproliferative action of ACE inhibitors on myocardium and the vascular wall, their hemodynamic effects, antiatherogenic actions, neurohormonal attenuation, and certain genetic issues may account for the ability of this class of drugs to reduce the risk for CAD-related events. Although ACE inhibitors can be expected to increase coronary blood flow when the renin-angiotensin system is activated and to reduce BP, ventricular filling pressure, and sympathetic drive, thus far an acute anti-ischemic action of these drugs has not been demonstrated. Unlike ACE inhibitors, which usually have class-specific effects, there are important differences in the clinical effects of various calcium antagonists. The first generation of dihydropyridine calcium-entry blockers has failed to demonstrate efficacy in secondary prevention of coronary artery events. However, verapamil reduces mortality in patients with normal left ventricular function. The antihypertensive efficacy of verapamil, its antiatherogenic action, and its ability to reverse left ventricular hypertrophy, to improve diastolic function, and to interfere with endothelium-derived contracting factors may also account for the improved survival of patients with CAD treated with this drug. Moreover, verapamil is also effective in the treatment of all types of angina because it reduces myocardial oxygen consumption as a result of its hypotensive effect and its ability to reduce heart rate, and it may also improve oxygen delivery to the myocardium because of its action on coronary vasodilatation. It is also important to consider that ACE inhibitors and calcium antagonists often induce the same beneficial effects through different mechanisms, thus allowing a synergistic action when the two classes of drugs are administered together.

Clinical Trials as Topic↗
PubMed1998

Dietary sodium restriction impairs endothelial effect of insulin.

Hyperinsulinemia and high salt intake represent two independent cardiovascular risk factors. However, it is still unknown whether the change in dietary salt intake may affect the ability of insulin to stimulate whole-body glucose uptake and to modulate endothelial function. Regarding this latter issue, we have recently demonstrated that insulin enhances endothelial-mediated alpha2-adrenergic vasorelaxation. In overnight-fasted, freely moving Wistar-Kyoto rats (10 to 12 weeks old), we assessed whole-body glucose uptake (in milligrams per kilogram per minute) during a euglycemic-hyperinsulinemic clamp (insulin infusion rate, 3 mU x kg(-1) x min(-1)) after 3 weeks of normal (NSD, 2% NaCl), high (HSD, 6% NaCl), and low (LSD, 0.6% NaCl) sodium diet. Three days after the clamp study, rats were killed to assess alpha2-adrenergic vasorelaxation evoked by UK 14,304 (10(-9) to 10(-6) mol/L) in aortic rings in control conditions and after insulin exposure (100 microU/mL). Different sodium intakes did not modify the mean blood pressure or the insulin-stimulated whole-body glucose uptake (NSD: 14+/-1.2, n=16; HSD: 15.4+/-1.7, n=14; LSD: 14.8+/-0.8, n=14; NS). In contrast, we confirmed the ability of insulin to enhance alpha2-adrenergic vasorelaxation during NSD and HSD (delta% of maximal relaxation, NSD: from 32+/-3% to 58+/-3.4%, n=9, P<0.01; HSD: from 33+/-3.8% to 59+/-3.5%, n=8, P<0.01), but this effect was impaired during LSD (delta% maximal relaxation, from 36+/-1.5% to 36+/-3.4%, n=8, NS). In conclusion, our data demonstrate that in Wistar-Kyoto rats, changes in dietary salt intake do not modify the insulin-stimulated whole-body glucose uptake. In contrast, LSD impairs the insulin potentiation of alpha2-adrenergic vasorelaxation, thus suggesting that dietary salt restriction provokes an impairment of insulin effect on endothelial function.

Adrenergic alpha-Agonists↗
PubMed1997

Insulin modulation of an endothelial nitric oxide component present in the alpha2- and beta-adrenergic responses in human forearm.

We explored in 51 normal subjects, distributed in various series of experiments, whether endothelium nitric oxide may play a role in insulin modulation of alpha2- and beta-adrenergic- evoked vascular responses. In particular, we examined the forearm blood flow response (FBF, ml.min-1.dl-1) to intrabrachial infusion of BHT-933 (0.5, 1, and 2 microg.min-1.dl-1) or isoproterenol (1, 3, and 6 ng. min-1.dl-1) in control conditions, during intrabrachial infusion of insulin alone (0.05 mU.kg-1.min-1) and associated with l-N-monomethylarginine (L-NMMA) (0.05 microg.min-1.dl-1), a nitric oxide synthase inhibitor. In control conditions both BHT-933 and isoproterenol induced a dose-dependent vascular response. Local hyperinsulinemia (deep venous plasma insulin 68.5+/-4 microU/ml) did not change basal FBF whereas attenuated BHT-933 vasoconstriction and enhanced isoproterenol vasodilation. L-NMMA reduced basal FBF and abolished the insulin effect on BHT-933 and isoproterenol response. To clarify whether a nitric oxide component is included in alpha2- and beta-adrenergic response and may be responsible for insulin vascular effect, we further examined BHT-933 and isoproterenol responses during nitric oxide inhibition. Interestingly, L-NMMA potentiated the BHT-933 vasoconstriction and attenuated the isoproterenol vasodilation and, in these conditions, insulin was no more able to exhibit its vascular effects. Finally, to rule out the possibility that the conteracting effect of L-NMMA may not be specifically related to insulin action, dose-response curves to phenylephrine (0.5, 1, and 2 microg.min-1.dl-1) or sodium nitroprusside (1, 2, and 4 microg.min-1.dl-1) were also performed. Both insulin and L-NMMA were unable to alter the phenylephrine-induced vasoconstriction and the sodium nitroprusside vasodilation. In conclusion, our data demonstrate an endothelial nitric oxide component in the alpha2- and beta-adrenergic vascular responses which is the target of the insulin vascular action.

Adrenergic alpha-Agonists↗
PubMed1997

Decreased blood pressure response in mice deficient of the alpha1b-adrenergic receptor.

To investigate the functional role of different alpha1-adrenergic receptor (alpha1-AR) subtypes in vivo, we have applied a gene targeting approach to create a mouse model lacking the alpha1b-AR (alpha1b-/-). Reverse transcription-PCR and ligand binding studies were combined to elucidate the expression of the alpha1-AR subtypes in various tissues of alpha1b +/+ and -/- mice. Total alpha1-AR sites were decreased by 98% in liver, 74% in heart, and 42% in cerebral cortex of the alpha1b -/- as compared with +/+ mice. Because of the large decrease of alpha1-AR in the heart and the loss of the alpha1b-AR mRNA in the aorta of the alpha1b-/- mice, the in vivo blood pressure and in vitro aorta contractile responses to alpha1-agonists were investigated in alpha1b +/+ and -/- mice. Our findings provide strong evidence that the alpha1b-AR is a mediator of the blood pressure and the aorta contractile responses induced by alpha1 agonists. This was demonstrated by the finding that the mean arterial blood pressure response to phenylephrine was decreased by 45% in alpha1b -/- as compared with +/+ mice. In addition, phenylephrine-induced contractions of aortic rings also were decreased by 25% in alpha1b-/- mice. The alpha1b-AR knockout mouse model provides a potentially useful tool to elucidate the functional specificity of different alpha1-AR subtypes, to better understand the effects of adrenergic drugs, and to investigate the multiple mechanisms involved in the control of blood pressure.

Animals↗
PubMed1997

Insulin enhances endothelial alpha2-adrenergic vasorelaxation by a pertussis toxin mechanism.

To investigate whether insulin effect on endothelium is related to a specific signal transduction pathway or reflects a more generalized action of the hormone, we studied in aortic rings of Wistar-Kyoto (WKY) rats the effects of the hormone on endothelium-dependent relaxations generated by acetylcholine, adenosine diphosphate, the selective alpha2-adrenergic agonist UK 14,304, and the calcium ionophore ionomycin. The responses were evaluated both in control conditions and after 30 minutes of exposure to three different levels of insulin (30, 100, and 500 microU/mL). Insulin failed to modify the phenylephrine aortic contractions and the relaxations induced by acetylcholine, adenosine diphosphate, and ionomycin. In contrast, both 100 and 500 microU/mL insulin were able to potentiate the UK 14,304-induced vasorelaxation (+96+/-19% and +91+/-12%, respectively). Pertussis toxin, which causes alpha2-adrenergic receptor Gi uncoupling, reduced the alpha2-adrenergic vasorelaxation and prevented the insulin potentiation of the response to UK 14,304. Furthermore, in primary cultured aortic endothelial cells from WKY, we evaluated the conversion of [3H]arginine to [3H]citrulline in response to acetylcholine, ionomycin, and UK 14,304, both in control conditions and during insulin exposure. Again, insulin did not affect basal citrulline production or the increase induced by acetylcholine and ionomycin, whereas it potentiated the response to UK 14,304. Finally, in aortic rings of spontaneously hypertensive rats, insulin treatment (100 and 500 microU/mL) was unable to enhance the alpha2-adrenergic vasodilator response; in vascular endothelial cells from spontaneously hypertensive rats, insulin did not potentiate the increase in citrulline production evoked by UK 14,304. In conclusion, insulin selectively enhances alpha2-adrenergic endothelial vasorelaxation through a pertussis toxin-sensitive mechanism, by potentiating endothelial nitric oxide production. This vasorelaxant mechanism is altered in spontaneously hypertensive rats.

Adrenergic alpha-Agonists↗