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Biomedical subjects

R Pedrinelli

Publications and source records attributed to R Pedrinelli.

At least 19 recordsLinked to original sources

Nonadrenergic sympathetic vascular control of the human forearm in hypertension: possible involvement of neuropeptide Y.

Animal experimental evidence suggests that neuropeptide Y (NPY) is coreleased with norepinephrine (NE) from sympathetic nerve endings and is involved in nonadrenergic neurogenic vascular control of skeletal muscle. We wished to determine whether these findings may be extended to humans. Forearm blood flow (venous occlusion plethysmography) and the regional overflows of NE and NPY-like immunoreactivity (NPY-LI) were studied at rest and during sympathetic nerve activation by lower body negative pressure (LBNP; -10 mm Hg, 10 min) in 10 hypertensive men before and after local alpha-adrenergic blockade by a dose of phenoxybenzamine (60 micrograms x 100 ml-1 x min-1 for 60 min), which most markedly attenuated responses to exogenous NE; propranolol (10 micrograms x 100 ml-1 x min-1) was present throughout. Phenoxybenzamine increased forearm blood flow at rest (11.5 +/- 1.0 vs. 3.9 +/- 0.3 ml x 100 ml-1 x min-1; p less than 0.001). LBNP-evoked reduction of forearm blood flow (37 +/- 2%, p less than 0.001) was attenuated (p less than 0.001) but not abolished (18 +/- 2%, p less than 0.001) by phenoxybenzamine. LBNP increased the overflow of NE from 5.0 +/- 1.7 to 8.2 +/- 3.0 pmol x 100 ml-1 x min-1 (p less than 0.05) and that of NPY-LI from -9.0 +/- 4.4 to 8.0 +/- 4.9 fmol x 100 ml-1 x min-1 (p less than 0.05) after phenoxybenzamine; effects on the evoked overflows of NE and NPY-LI before phenoxybenzamine were slight. Prejunctional inhibitory alpha-adrenoceptors may thus modulate NPY release as well.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult

Calcium entry blockade and agonist-mediated forearm vasoconstriction in hypertensive patients. Difference between nicardipine and verapamil.

The interference by nicardipine and verapamil with the response to vasoactive stimuli, such as lower body negative pressure and angiotensin II, has been evaluated in the forearm of hypertensive patients. Forearm blood flow was monitored during the intraarterial infusion of either drug at rates equieffective on basal flow. Nicardipine blunted the peak forearm vasoconstrictor action of lower body negative pressure and a comparable result was obtained when angiotensin II was administered intraarterially. In spite of a comparable increase in forearm flow, nicardipine was more potent than verapamil in inhibiting vasoconstriction following both stimuli. Thus, nicardipine suppressed regional vascular reactivity, probably by blockade of the influx of extracellular calcium, in response to receptor activation, since both alpha-adrenergic and angiotensin II receptor-mediated vasoconstrictor responses were attenuated. However, the results of the comparison with an unrelated calcium entry blocker, such as verapamil, may suggest that nicardipine, and possibly other dihydropiridine derivatives, preferentially antagonize agonist-mediated vasoconstriction in the human forearm.

Angiotensin II

An atrial natriuretic factor analogue at low doses attenuates forearm reflex vasoconstriction to cardiopulmonary receptor deactivation in patients with hypertension.

Contrasting data exist about a possible modulation of the autonomic function by atrial natriuretic factor (ANF) in human beings, particularly at low, biologically, significant concentrations. We have evaluated that possibility by increasing plasma ANF levels through the infusion of a synthetic analogue (WY-47,663, anaritide) in five male patients with mild to moderate uncomplicated hypertension. Nonhypotensive lower body negative pressure (-10 mm Hg x 5 min) was used to selectively deactivate cardiopulmonary receptors and to stimulate sympathetic efferent tone reflexogenically. ANF was given at either a low rate (0.005 micrograms/kg/min x 60 min, which was previously shown to increase plasma ANF in a range compatible with physiologic stimuli) or at a high rate (0.05 micrograms/kg/min x 60 min, each). Administration of ANF was preceded and followed by vehicle infusion (Haemacell x 30 min). Forearm blood flow (venous plethysmography), intraarterial blood pressure, and heart rate were monitored continuously, and venous immunoreactive ANF, plasma renin activity, aldosterone level, and venous hematocrit were measured at the end of both control and infusion periods. Arterial norepinephrine values, an indirect index of sympathetic discharge, were measured at rest and during lower body negative pressure conditions. Graded systemic ANF infusion increased immunoreactive ANF and venous hematocrit, decreased aldosterone level and plasma renin activity, whereas resting norepinephrine levels, blood pressure, and heart rate did not change. Lower body negative pressure decreased forearm blood flow during vehicle infusion, but it lost its vasoconstrictor effect during infusion of ANF. To identify the site of that inhibitory action, ANF was also infused into the brachial artery at rates that raised local but not systemic levels of immunoreactive ANF.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult

Heterogeneous interference of nicardipine, verapamil, and diltiazem with forearm arteriolar responsiveness to adrenergic stimulation in hypertensive patients.

The interference of intraarterial nicardipine, verapamil, and diltiazem with the forearm vascular response to graded exogenous norepinephrine was evaluated in hypertensive patients. Nicardipine antagonized the vasoconstrictor effect of norepinephrine in a dose-dependent manner, whereas verapamil was ineffective, suggesting that functional alpha-adrenergic antagonism may participate in the vasodilatory and possibly the antihypertensive effect. Nicardipine also blunted the vasoconstriction to lower-body negative pressure and the action of angiotensin II administered intraarterially. Despite a comparable increase in basal forearm flow, verapamil was less potent than nicardipine in inhibiting vasoconstriction after both stimuli. Therefore nicardipine suppressed preferentially regional vascular reactivity, probably by blockade of the influx of extracellular calcium in response to receptor activation, because both alpha-adrenergic and angiotensin II receptor-mediated vasoconstrictor responses were attenuated. At variance with both nicardipine and verapamil was potentiation of the responses to norepinephrine after the administration of diltiazem. Because intraarterial propranolol abolished that potentiating action and the local vasodilatation to isoproterenol was clearly reduced, diltiazem probably interfered also with beta-adrenergic receptor-mediated vasorelaxing mechanisms in human forearm arterioles. The data further stress the heterogeneity of calcium channel blockers in humans.

Arterioles

Calcium entry blockade and adrenergic vascular reactivity in hypertensives: differences between nicardipine and diltiazem.

The interference of nicardipine and diltiazem infused into the brachial artery at systemically ineffective rates, with the forearm vascular response to graded exogenous norepinephrine, was evaluated in hypertensive patients. Nicardipine (1 and 3 micrograms/dl forearm tissue/min in both absence and presence of propranolol) increased forearm blood flow (venous plethysmography) and antagonized dose dependently the vasoconstrictor effect of norepinephrine, suggesting that functional alpha-antagonism may participate in the vasodilating and possibly the antihypertensive effect of the drug. On the contrary, no antagonism but rather potentiation of the responses to norepinephrine occurred after diltiazem (0.5 and 1 microgram/dl forearm tissue/min). Because intra-arterial propranolol abolished that potentiating action of the drug, whereas the local vasodilation to isoproterenol was clearly reduced, diltiazem probably interfered with beta-adrenergic receptor-mediated vasorelaxing mechanisms in human forearm arterioles. The data further stress the heterogeneity of calcium entry blockers in humans.

Adrenergic alpha-Antagonists

Theophylline is an antagonist of adenosine in human forearm arterioles.

The pharmacodynamics of theophylline in humans is attributed to the inhibition of phosphodiesterase activity, a concept based on in vitro studies using drug concentrations much higher than those achieved by therapeutic doses. Recent in vitro studies suggest that theophylline might act as an antagonist of adenosine. This hypothesis was tested in hypertensives by assessing the effect of theophylline on adenosine mediated vasodilation. Drugs were infused into the brachial artery while forearm blood flow (venous plethysmography) was continuously monitored. Adenosine, infused cumulatively (5, 15, and 50 micrograms/min for 3 min each; n = 5), caused a dose-dependent vasodilation that was clearly blunted in the presence of theophylline in a dose not affecting basal arterial flow (1000 micrograms/min for 20 min). On the contrary, papaverine, a selective phosphodiesterase activity inhibitor, infused at two increasing doses (100 and 300 micrograms/min for 20 min, n = 5), did not affect adenosine mediated vasodilation. Our data show that theophylline acts as a specific antagonist of adenosine in humans, an effect which might be relevant for its pharmacological action.

Adenosine

Does a digoxin-like substance participate in vascular and pressure control during dietary sodium changes in patients with primary aldosteronism?

To evaluate the importance of an endogenous sodium pump inhibitor in the pathogenesis of low renin human hypertension, the urinary excretion of a digoxin-like immunoreactive substance (DLIS) was measured in eight patients with primary aldosteronism (n = 5, with adenomas) during two sequential 1-week periods of low- (20 mmol/l NaCl) and high- (200 mmol/l NaCl) sodium intake. DLIS excretion increased consistently during high-sodium intake while urinary aldosterone, plasma renin activity, cortisol and adrenocorticotropic hormone did not change. Although blood pressure showed a time-course parallel to that of the urinary DLIS, the blood pressure increments were not accompanied by evidence of vasoconstriction since forearm blood flow (plethysmographic technique) increased and forearm vascular resistances were reduced. Moreover, the reactivity of forearm arterioles to local norepinephrine was unchanged during the period of low- and high-salt intake, despite the fact that an endogenous sodium pump inhibitor should, supposedly, sensitize the responses to an adrenergic agonist. Finally, forearm vasoconstrictor responses to ouabain, a pharmacological Na+,K(+)-ATPase antagonist, were potentiated during the high-salt diet, a result not expected if an increased number of sodium pumps were occupied by an endogenous inhibitor. These results provide unequivocal evidence for a modulation by salt intake of the urinary excretion of a DLIS in patients with primary aldosteronism. This substance might participate in the regulation of body fluid volume in this syndrome and possibly in other physiological conditions. However, no evidence could be found for a cause--effect relationship between blood pressure and DLIS increments during high-salt intake, at least during the short-term course of the study.

Aldosterone

Lack of correlation between cardiac mass and arteriolar structural changes in mild-to-moderate hypertension.

A morphological restructuring of cardiac and arteriolar tissue is common in hypertension. The parallel evolution of these two processes as a compensatory response to pressure overload is a frequently assumed but unsubstantiated hypothesis. To evaluate this possibility, we have concomitantly measured left ventricular mass (LVM; two-dimensional echo) and minimal forearm vascular resistance (FVR; derived from the ratio of intra-arterial blood pressure: forearm blood flow by venous plethysmography) at maximal postischemic (13 min ischemia + 1 min hand exercise) reactive hyperemia. The study was performed on 29 essential hypertensive patients (15 males, 14 females, aged 50 +/- 10 years) who had not been undergoing treatment for hypertension for at least 15 days at the time of study. Minimum FVR was taken as a hemodynamic index of the integrated arteriolar lumen at the forearm level. LVM index and minimum FVR ranged from normal to clearly altered values. In spite of a wide spread of values, no correlation existed between the individual values of the two variables. Systemic mean blood pressure correlated with minimum FVR and tended to correlate with LVMI. Thus, morphological restructing of cardiac and arteriolar tissue does not seem to evolve in parallel in human hypertension. Pressure overload may contribute to cardiovascular hypertrophy, but other unrelated mechanisms may also underlie the development of cardiac and arteriolar abnormalities of human hypertension.

Arterioles

Atrial natriuretic factor as a vasodilator agent in hypertensive patients.

To investigate the role of Atrial Natriuretic Factor (ANF) in modulating arteriolar tone in hypertension, a synthetic 25 AA human ANF-analogue (anaritide) was infused intraarterially in the forearm vascular bed of five patients with mild hypertension. A dose-dependent increase in blood flow (plethysmographic technique) was seen at rates covering a thousand-fold range (0.008, 0.08, 0.8, 8.0 micrograms/dl tissue/min x 15 minutes each). At the lowest infusion rate, the forearm blood flow increment was associated with changes in local venous ANF concentrations comparable with those reported during biological stimuli in hypertensive man and consistent with an ANF physiologic role in forearm arterioles of hypertensive patients. However, at local venous concentrations greater than 1000 pg/ml, ANF did not relax forearm vessels by more than about one-fourth of the total forearm vasodilator capacity (as assessed through a maximally active ischemic stimulus). These data confirm the low potency of ANF as an endogenous vasodilator, although vasodilator potency is not a necessary requirement for physiologic systems involved in the regulation of muscular vascular tone. Systemic arterial pressure, heart rate, and contralateral flow did not change during the study in spite of the markedly increased peripheral ANF levels recirculating from the local forearm administration. This behavior indicates that arteriolar vasodilation is apparently not the main mechanism of action of ANF on systemic hemodynamics in hypertensive patients.

Adult

Reactive hyperemia during short-term blood flow and pressure changes in the hypertensive forearm.

The aim of the present study was to further validate our method for the determination of minimal forearm vascular resistance after ischemia (13 min arterial occlusion and 1 min hand exercise) in patients with hypertension. This parameter, calculated as the ratio of mean blood pressure (intra-arterial recordings on the experimental side) to forearm blood flow (strain-gauge venous plethysmography), was measured basally and after either increasing (through unrelated vasodilators such as sodium nitroprusside or the calcium antagonist nicardipine in six mild-to-moderate uncomplicated hypertensives) or decreasing (norepinephrine, n = 4) flow without changes in systemic pressure. In spite of the divergent starting flow values, minimal postischemic forearm vascular resistance was unchanged, indicating a lack of relationship with functional arteriolar tone and the achievement of maximal dilatation. In two additional groups of patients, systemic arterial pressure was decreased by approximately equipotent oral doses of either nifedipine, a calcium antagonist (n = 6), or captopril, an angiotension converting enzyme inhibitor (n = 5). Under these conditions, minimal forearm vascular resistance was unchanged from pretreatment values, suggesting that local autoregulatory mechanisms were overridden during the reactive hyperemia, and that the vessel lumen was dependent on the distending pressure. Overall, the data show that our experimental conditions are suitable for measuring minimal forearm vascular resistance as a functional correlate of the morphological status of systemic arterioles in arterial hypertension.

Adult

Sympathetic nervous system-dependent vasoconstriction in humans. Evidence for mechanistic role of endogenous purine compounds.

Purine compounds modulate sympathetic neurotransmission; this modulation decreases nervous discharge by stimulating presynaptic inhibitory adenosine receptors, an effect antagonized by theophylline, and causes vasoconstriction through the stimulation of postsynaptic ATP receptors. In humans we evaluated the effect of local theophylline, which was infused into the brachial artery at the rate of 100 micrograms/100 cc/min, on the arteriolar sympathetic vasoconstriction induced by applying a lower-body negative pressure. Forearm blood flow changes were measured by strain-gauge venous plethysmography. Theophylline, which at this dosage blunted the vasodilator effect of adenosine (the physiological agonist for the P1 purinoceptor), significantly increased lower-body negative pressure-mediated vasoconstriction. To evaluate whether neurotransmitters different from norepinephrine participate in the vasoconstrictor effect of theophylline, we repeated the previous experiment in the presence of phenoxybenzamine, which was infused at a dose (60 micrograms/100 cc/min) that abolished the vasoconstrictor effect of norepinephrine. Also, after alpha-adrenoceptor blockade, theophylline continued to increase sympathetic vasoconstriction. Our data confirm that purinergic receptors and neurotransmitters also participate in endogenous sympathetic vasoconstriction in humans.

Adenosine

Effects of insulin on hemodynamics and metabolism in human forearm.

We investigated the vascular response (blood flow and resting vascular resistance) and the metabolic response (exchange of metabolites and respiratory gases) to local insulin administration in the forearms of healthy young volunteers with the use of the perfused-forearm technique. In the postabsorptive state, the deep tissues of the forearm (mostly skeletal muscle) took up glucose (mean +/- SE 1.09 +/- 0.17 mumol.min-1.dl-1 forearm vol), beta-hydroxybutyrate (0.267 +/- 0.130 mumol.min-1.dl-1), and O2 (9.96 +/- 1.02 mumol.min-1.dl-1) and released lactate (0.284 +/- 0.098 mumol.min-1.dl-1), glycerol (0.029 +/- 0.012 mumol.min-1.dl-1), citrate (0.091 +/- 0.030 mumol.min-1.dl-1), alanine (0.184 +/- 0.044 mumol.min-1.dl-1), CO2 (7.36 +/- 0.97 mumol.min-1.dl-1), and protons (12.1 +/- 1.4 pmol.min-1.dl-1). Forearm blood flow (by venous occlusion plethysmography) was 2.95 +/- 0.18 ml.min-1.dl-1, and intra-arterial systolic/diastolic blood pressure was 116 +/- 3/76 +/- 2 mmHg. Local indirect calorimetry indicated dominance of fat as the oxidative substrate (RQ 0.76 +/- 0.09) and an energy expenditure rate of 1.03 +/- 0.11 cal.min-1.dl-1 forearm vol. One hundred minutes of intra-arterial insulin infusion (deep venous plasma insulin concn of 125 +/- 11 microU/ml) had no detectable effect on forearm blood flow, resting forearm vascular resistance, heart rate, or blood pressure. Local hyperinsulinemia significantly stimulated glucose uptake (to 4.79 +/- 0.61 mumol.min-1.dl-1 forearm vol, P less than 0.001), lactate and pyruvate release (to 0.710 +/- 0.093 and 0.032 +/- 0.016 mumol.min-1.dl-1 forearm vol, respectively; P less than 0.01 for both), potassium uptake (0.76 +/- 0.22 mueq.min-1.dl-1, P less than 0.001), and free fatty acid uptake (0.123 +/- 0.041 mumol.min-1.dl-1 forearm vol, P less than 0.05); glycerol balance switched to a net uptake (P less than 0.001), alanine release was restrained by 33% (P less than 0.05), and beta-hydroxybutyrate and citrate release were unchanged. Despite these metabolic changes, local rates of substrate oxidation and energy expenditure were not altered by insulin. In contrast, forearm proton release was significantly stimulated by insulin (to 14.8 +/- 1.4 pmol.min-1.dl-1, P less than 0.02). Proton release was also found to be directly related to resting forearm vascular resistance independent of the effect of insulin (multiple r = 0.64, P less than 0.001).(ABSTRACT TRUNCATED AT 400 WORDS)

3-Hydroxybutyric Acid

Calcium entry blockade and agonist-mediated vasoconstriction in hypertensive patients.

The effects of two chemically unrelated calcium channel blockers--nicardipine and verapamil--on vascular responses to exogenous norepinephrine were evaluated in uncomplicated hypertensive patients. Each drug was infused into the brachial artery at rates that did not affect systemic blood pressure or heart rate, and forearm blood flow was measured using strain gauge venous plethysmography. Nicardipine 1 microgram/100 ml forearm tissue/min dilated the forearm arterioles and antagonized the vasoconstrictor effect of norepinephrine, whereas verapamil 1 microgram/100 ml tissue/min was ineffective, even though both drugs relaxed basal tone to the same extent. The difference between nicardipine and verapamil was also evident when reflex forearm vasoconstriction was elicited by the application of a lower body negative pressure and the drugs were infused intra-arterially at 1 and 3 micrograms/100 ml tissue/min, respectively. To evaluate whether a comparable behavior might also hold for nonsympathomimetic agents, increasing doses of angiotensin II were administered to the forearm vascular bed after pretreatment with either nicardipine or verapamil. Both drugs increased forearm blood flow, but only nicardipine antagonized the effect of angiotensin II in the forearm, showing that the impairment of vasoconstrictor mechanisms was not dependent on a specific receptor. Important differences seem to exist between nicardipine and verapamil with regard to agonist-mediated vasoconstriction in hypertensive patients, which is consistent with the heterogeneity of calcium channel blockers as a pharmacological class. Preferential antagonism of a series of vasoconstrictor stimuli may characterize the vasodilatory and, possibly, the antihypertensive effect of nicardipine.

Adrenergic alpha-Agonists

Indenolol, a beta-blocker with partial agonism at vascular beta-adrenoceptors.

Intrinsic sympathomimetic activity may attenuate some effects caused by treatment with beta-adrenoceptor blockers. Indenolol is a nonselective beta-adrenoceptor antagonist whose sympathomimetic properties have been shown in vitro but not in human beings. We infused indenolol cumulatively (5, 15, and 50 micrograms/100 ml tissue per minute for 15 minutes each, preceded by an infusion of saline solution) into the brachial arteries of nine hypertensive patients. Forearm blood flow (venous plethysmography), mean arterial pressure, and heart rate were monitored. During infusion at 5 micrograms/100 ml tissue per minute, forearm blood flow did not change, but it did increase dose-dependently at the greater infusion rates. This action was determined to be mediated by beta-adrenoceptor stimulation because propranolol (10 micrograms/100 ml tissue per minute for 15 minutes), given before treatment and then concomitantly with indenolol, abolished it (n = 5). Indenolol vasodilated forearm arterioles and this effect was antagonized by beta-blockade, thus demonstrating vascular intrinsic sympathomimetic activity. This property may contribute to its therapeutic action in human beings.

Adrenergic beta-Antagonists

Calcium entry blockade and alpha-adrenergic vascular reactivity in human beings: differences between nicardipine and verapamil.

The interference by two unrelated calcium entry blockers, nicardipine and verapamil, with the forearm vascular response to graded exogenous norepinephrine was evaluated in two groups (n = 6 each) of patients with uncomplicated hypertension. Drugs were infused into the brachial artery at systemically ineffective rates and forearm blood flow was measured by venous plethysmography. Nicardipine (1 microgram/dl forearm tissue/min) relaxed forearm arterioles and antagonized the vasoconstrictor effect of norepinephrine, whereas verapamil (1 microgram/dl forearm tissue/min) was ineffective, although vasodilating to a comparable extent. Therefore, functional alpha-antagonism may contribute to the vasodilating and, possibly, the antihypertensive effect of nicardipine but, apparently, not verapamil. The data further stress the heterogeneity of calcium channel entry blockers even in human beings.

Adult

Sympathetic vasoconstriction as a mechanism of action of ouabain in forearm arterioles of hypertensive patients.

1. The interaction of ouabain, a Na+/K+ adenosine 5'-triphosphatase inhibitor, with sympathetic mechanisms of vasoconstriction, as well as its possible site(s) of action, were investigated in forearm arterioles of patients with uncomplicated hypertension. 2. Intra-arterial infusion of ouabain per se decreased forearm blood flow without changes in systemic arterial pressure or contralateral flow. However, the vasoconstrictor effect of the glycoside was abolished after local pretreatment with either phentolamine, a competitive alpha-adrenoceptor antagonist, or bretylium tosylate, a neurotransmitter blocker. 3. To exclude a non-specific effect due to the vasodilatation, a similar protocol was performed using histamine, which acts independently of sympathetic mechanisms. The vascular effect of ouabain was maintained in spite of histamine-induced increases in forearm blood flow even greater than those obtained from either blocker. 4. To discriminate between pre- and post-synaptic site(s) of action of ouabain, exogenous noradrenaline was infused intra-arterially after inactivation of local neurotransmitter release by bretylium, thus causing direct postsynaptic vascular alpha-adrenoceptor stimulation. Under these conditions, noradrenaline decreased forearm blood flow irrespective of the presence or absence of ouabain. 5. Thus, local sympatholysis by drugs acting on different levels of the sympathetic neuroeffector junction abolished the effect of ouabain, whereas histamine did not influence it. The data provide positive evidence for an effect of ouabain on sympathetically mediated vasoconstriction. This action is apparently not exerted at a postsynaptic site but possibly by enhancing neurotransmitter release. 6. If a circulating endogenous ouabain-like Na+/K+ adenosine 5'-triphosphatase inhibitor is relevant to the development of hypertension in man, it might act through a similar mechanism.

Arterioles

Forearm vasodilatory capacity in patients with syndrome X: a comparison with normal and hypertensive subjects.

Minimal forearm vascular resistances during maximal postischaemic vasodilation were measured in normotensive subjects with syndrome X, a condition characterized by angina and normal coronary arteries, in which a reduced coronary and systemic vasodilatory capacity has been reported. Age- and sex-matched normals and essential hypertensives constituted the control groups. The syndrome X patients had a significantly higher minimal forearm vascular resistance than the normals, indicating that arteriolar alterations may occur in the normotensive state and therefore cannot be considered solely as a consequence of hypertension.

Angina Pectoris