Hypertension due to pheochromocytoma is generally considered to be a straightforward, direct consequence of the elevated concentrations of circulating catecholamines. However, clonidine, a centrally acting antihypertensive drug, has been reported to lower blood pressure in patients with pheochromocytoma, suggesting the possibility that the sympathetic nervous system is involved in the ...

Intramuscular (im) pentamidine isethionate can cause substantial local pain and inflammation at the injection site. This drug is being used more frequently in recent years to treat Pneumocystis pneumonia, particularly in patients with acquired immunodeficiency syndrome. Clinicians began administering it iv despite warnings that iv administration might cause severe hypotension. ...

Intracerebroventricular (i.c.v.) administration of thyrotropin-releasing hormone (TRH) in a range from 0.1 to 100 micrograms induced a dose-related increase in blood pressure in conscious rats, whereas TRH-free acid (TRH-OH) and histidyl-proline diketopiperazine (His-Pro-DKP), metabolites of TRH, did not. The blood pressure responses to intravenous (i.v.) injection of 5 mg/Kg TRH ...

The cardiovascular effects of selective alpha 1 and alpha 2 agonists and antagonists injected into the nucleus tractus solitarii (NTS) were studied in urethane-anesthetized rats. Methoxamine (0.3-3 micrograms) injected bilaterally into the NTS caused a dose-dependent increase in blood pressure and heart rate. Phenylephrine (6 micrograms) and an imidazolidine derivative ...

Transdermal clonidine (TTSC) has been proposed as a means to improve compliance to treatment of hypertensive patients because of the reported 7-day duration of its antihypertensive effect. However, no detailed information is available on the onset, the time course, and the day and night distribution of this effect throughout the ...

The effect of the intravenous administration of dihydroergotoxine (6 micrograms/kg) on arterial blood pressure, heart rate, and plasma concentrations of norepinephrine and 3,4-dihydroxyphenylacetic acid (the deaminated dopamine metabolite) was studied in 20 subjects with essential hypertension (8 men and 12 women aged 32-68 years old, World Health Organization Class I-II). ...

To evaluate the role of the sympathetic nervous system in essential hypertension and the influence of clonidine, 28 male subjects with mild to moderate hypertension were either treated with low-dose clonidine (n = 14, mean age: 42.4 +/- 2.1 years) or were randomized to a nontreated control group (n = ...

The action of several dopamine agonists on blood pressure was investigated. In dogs, apomorphine induced a decrease in blood pressure and an increase in heart rate. These effects were suppressed by intravenous haloperidol or phentolamine. Intravenous but not intracisternal domperidone suppressed the hypotensive responses elicited by intravenous or intracisternal apomorphine. ...

In renal artery stenosis activation of the renin-angiotensin system elevates blood pressure by direct peripheral effects and probably through stimulation of sympathetic activity, which can be induced by angiotensin-II either centrally or peripherally. In animals specific brain lesions and afferent renal denervation can either attenuate or prevent renovascular hypertension. We ...

To evaluate the mechanisms of the hypertensive action of dopamine and its dependence on its metabolic patterns we infused a borderline hypertensive dose of free dopamine into healthy subjects. The moderate rise in systolic and diastolic blood pressure with an expected considerable increase of plasma free dopamine concentrations was associated ...

Plasma prostaglandins (PGs; PGE2, PGF2 alpha, 6-keto-PGF 1 alpha and TXB2) and plasma renin activity (PRA) were measured in 94 end-stage renal disease (ESRD) patients including 15 undialyzed, 74 maintenance-hemodialyzed and 5 anephric patients, and in 27 healthy controls. In the healthy controls, 6-keto-PGF 1 alpha inversely correlated with age, ...

Since left ventricular hypertrophy is considered to be a precursor of later hypertensive heart failure, a treatment that can prevent or even reverse myocardial hypertrophy is a highly desirable goal. In order to evaluate which type of antihypertensive treatment is able to induce regression of hypertensive hypertrophy, experimental and clinical ...

We have studied the efficacy of clonidine hydrochloride administered transdermally once a week for 9 to 15 weeks in 12 patients with mild to moderate hypertension. Clonidine reduced both supine and standing blood pressures on average, but only 8 subjects were responders, i.e. had a decrease in supine diastolic blood ...

Three (and possibly all four) elderly hypertensive patients who were followed sequentially after discontinuation of transdermal clonidine monotherapy manifested a rapid rise in blood pressure to levels above control (pre- and post-therapy) readings. No signs of an "overshoot" in plasma norepinephrine levels or symptoms of beta-adrenergic overactivity were seen. Such ...

Cats and rats anaesthetized with pentobarbital were used to study the central cardiovascular effects of the clonidine displacing substance (CDS). The potential influence of centrally applied CDS on the cardiovascular effects of clonidine was also investigated in both species. CDS is a brain substance which is not a catecholamine (CA) ...

The effects of various alpha adrenoceptor agonists and antagonists injected into the spinal subarachnoid space on blood pressure and heart rate were investigated in pentobarbital-anesthetized male rats. A dose-dependent decrease in blood pressure and heart rate was induced by intrathecal injections of clonidine (0.3-3 micrograms), at the T6-T7 level. Guanabenz ...

Animal studies have suggested that vasoconstrictor alpha-2 adrenoreceptors exist on vascular smooth muscle cells. We tested this hypothesis in a patient with severe autonomic failure who demonstrated a pressor response to oral clonidine (a selective alpha-2 adrenoreceptor partial agonist). After clonidine 0.8 mg orally, mean arterial pressure rose by 54 ...

The central nervous system may initiate or maintain hypertension in humans by a variety of mechanisms. Increased cerebral pressor activity can cause hypertension in some patients with the Guillain-Barré syndrome, where disinhibition of cerebral centres may result from an afferent baroreflex lesion. The brain itself initiates hypertension in patients with ...

Previous studies have shown that some antihypertensive drugs, beside controlling arterial pressure (AP), reverse left ventricular hypertrophy (LVH) by reducing adrenosympathetic activity. The aim of our study was to evaluate the relationship between AP levels, echocardiographic LVH and 24-h urinary excretion of epinephrine (UE) and norepinephrine (UNE) in 23 previously ...

We investigated the relationship between hypertension and increased sympathoadrenal activity in previously normotensive, stable maintenance hemodialysis patients (uremics) who developed hypertension subsequent to the onset of chronic renal failure. In age-matched groups, supine morning plasma norepinephrine (NE) concentrations (pg/ml) were elevated in uremics (401 +/- 26, p less than 0.00001, ...

In a six-week multicenter, double-blind comparison study, moxonidine and clonidine HCl were tested in 122 and 30 outpatients, respectively, with mild to moderate hypertension (World Health Organization stage I and II; highest measured diastolic blood pressure, 90 to 115 mm Hg). Each agent reduced systolic and diastolic blood pressure to ...

Opioid peptides are thought to be involved in blood pressure regulation, possibly via an interaction with the sympathetic nervous system (CNS). To further elucidate this hypothesis the plasma concentrations of beta-endorphin, leucine-enkephalin and noradrenaline were determined overnight (9 p.m. to 8 a.m.) in young patients with mild essential hypertension and ...

Ketanserin, when infused into the left thoracic vertebral artery of chloralose-anaesthetized cats, induced a significantly stronger hypotensive effect than when administered via the systemic circulation. The effect of ketanserin, which is initiated most likely in the pontomedullary region of the brain, proved to be dose dependent. The central hypotensive effect ...

To determine whether clonidine treatment affects cardiopulmonary baroreflex induced sympathetic activation, we assessed the hemodynamic and hormonal responses to lower body negative pressure (LBNP) before and after 3 weeks of treatment with low-dose (0.2 mg daily) clonidine in eight older (mean age, 62 years) patients with established mild-to-moderate hypertension. Arterial ...

1. The alpha 2-adrenergic agonist clonidine was given by aortic injection to three groups of unanaesthetized fetal lambs in utero near term. One group was intact, the second had the brain stem transected just above the pons, and the third had bilateral section of the carotid sinus nerves and cervical ...

Following an open trial of clonidine hydrochloride (3 to 8 micrograms/kg/day for 12 weeks), we studied the behavioral, cardiovascular, and neurochemical effects of abrupt clonidine withdrawal in seven patients with Tourette's syndrome aged 9 to 13 years. Five patients showed marked worsening of tics. After reinitiation of clonidine therapy, the ...

Clonidine hydrochloride, an alpha 2-adrenergic receptor agonist that decreases noradrenergic function, was administered to 21 healthy subjects and 26 drug-free patients with agoraphobia and panic attacks. Clonidine produced significantly greater decreases in plasma MHPG levels and sitting and standing diastolic blood pressure and significantly smaller increases in growth hormone levels ...

Alpha-adrenoceptor (alpha-AR) mechanisms may contribute to systolic and diastolic dysfunction of the left ventricle. Centrally acting alpha 2-AR agonist drugs, including methyldopa, clonidine, and guanabenz, activate brainstem alpha 2-AR and this activation results in a decrease in overall sympathetic tone and an increase in parasympathetic tone. Peripherally acting alpha 1-AR ...

In 30 patients with mild essential hypertension, clonidine hydrochloride was delivered from a skin patch reservoir designed to release medication at a constant rate for seven days. After a four-week washout period, patients were randomized (double-blind) into a clonidine- or a placebo-treated group. Clonidine or placebo was then given for ...

Clonidine is a centrally acting antihypertensive agent used in the management of essential hypertension. Oral clonidine loading is now used frequently in the management of hypertensive urgencies (ie, increases in arterial pressure not associated with acute, life-threatening end-organ injury). We report the case of a patient with an acute inferior ...

Worldwide clinical trial data concerning the pharmacokinetic and pharmacodynamic characteristics of the clonidine transdermal therapeutic system (TTS) are reviewed with reference to its antihypertensive efficacy. The amount of clonidine delivered to the systemic circulation is a direct function of TTS size. After initial patch application, there is a delay of ...

The effectiveness of transdermally administered clonidine using Catapres-TTS patches applied once a week was assessed in the control of mild to moderate hypertension by 16 general practitioners in 135 subjects. Following two weeks on placebo patches, subjects with mean seated diastolic pressures 90 to 104 mmHg were titrated to one, ...

Intravenous clonidine was used to treat systolic hypertension (systolic blood pressure greater than 160 mm Hg) in 15 patients with acute myocardial infarction and documented sympathetic overactivity (high plasma norepinephrine). Its effects on haemodynamics and blood gases were studied. After one hour, clonidine significantly reduced the systolic (195 +/- 7 ...

We studied the effects of clonidine, an alpha 2-adrenoreceptor agonist, and yohimbine, an alpha 2-adrenoreceptor antagonist, on blood pressure, heart rate, and plasma catecholamines in 12 patients with autonomic dysfunction. Clonidine (0.1 mg, orally) lowered blood pressure 18 +/- 3 torr in six subjects and raised it 5 +/- 1 ...

The subtypes of postjunctional alpha adrenoceptors in the feline pulmonary vascular bed were studied by using selective alpha-adrenoceptor agonists and antagonists. Under conditions of controlled pulmonary blood flow and constant left atrial pressure, intralobar injections of the alpha 1 agonists phenylephrine and methoxamine, and the alpha 2 agonists UK 14,304 ...

The location of two distinct subtypes of alpha adrenoceptors on blood vessels is now well established. The present study was designed to assess the relative contribution of alpha-1 and alpha-2 adrenoceptors to the maintenance of sympathetic vasoconstrictor tone to the canine hindlimb. Bilateral hindlimb perfusion was carried out at controlled ...

To study the effect of inhaled clonidine on broncho-obstruction in asthmatics, 10 patients with extrinsic asthma were broncho-provoked twice with an allergen that had been shown to give positive skin prick test results. Before the provocations, saline or clonidine (75 micrograms) was inhaled via a DeVilbiss no. 40 nebulizer. Clonidine ...

To determine if mature coronary collateral vascular smooth muscle contains functioning alpha-adrenergic receptors, we studied 13 dogs, 6-10 months after circumflex ameroid occlusion. Regional myocardial blood flow was measured with radioactive microspheres in a blood-perfused heart preparation at constant aortic pressure (80 mm Hg). Normal zone resistance was calculated as ...

The influence of circulating noradrenaline (in this context primarily a non-selective alpha agonist) and the alpha 1 selective agonist phenylephrine on bronchial tone, blood pressure, and heart rate was studied in eight patients with exercise induced asthma and eight age and sex matched controls. All subjects refrained from taking treatment ...

The pharmacokinetics and pharmacodynamics of trimazosin are described following both intravenous and oral administration to 6 normotensive, male volunteers. The IV and oral drug and metabolite (1-hydroxytrimazosin) concentration data are fitted simultaneously to the same pharmacokinetic model. The pharmacodynamic response, change in systolic blood pressure following 5 min in the ...

The stainless steel cannula inserting method was used to observe vascular effects of 7 vasoactive substances on the isolated and cold-stored digital artery of the monkey. The arterial preparation was suspended in a bath at 37 degrees C and perfused with Ringer's solution under constant flow rate. Drugs were administered ...

In order to determine whether pharmacologically-induced alterations in the spontaneous activity of neurons in the locus coeruleus are associated with changes in blood pressure, the activity of the locus coeruleus and blood pressure were recorded simultaneously in anesthetized rats after the administration of agents known to affect both of these ...

Xylazine and clonidine, given intravenously, cause an increase in airway pressure in the anaesthetized, ventilated sheep. This increase was dose dependent and was not mediated by histamine, nor was it blocked by the alpha 1-adrenoceptor antagonist prazosin. However, the increase was abolished by the alpha 2-adrenoceptor antagonist, idazoxan. When the ...

CBF, as measured by the clearance of 133Xe or 85Kr in the pentobarbital-anesthetized cat, displays a monotonic increase as the PaCO2 is elevated over a range of 20-60 mm Hg (slope Xe, 1.65 +/- 0.14 ml/100g/min/mm Hg; slope Kr, 1.40 +/- 0.11 ml/100 g/min/mm Hg). Clonidine (20 micrograms/kg i.v.), a ...

We report here that topical application of clonidine displacing substance (CDS), an endogenous brain extract, directly in the nucleus reticularis lateralis (NRL) region of anaesthetized cats regularly produced hypertension. CDS (5 units) increased the mean blood pressure by 40 +/- 8%. Pretreatment of anaesthetized rabbits with intracisternal CDS (500 units) ...

The present studies examined the role of alpha 1- versus alpha 2-adrenoceptors in the cardiovascular effects of clonidine administered into the anterior hypothalamic/pre-optic (AH/PO) region of the forebrain by the push-pull perfusion technique. Push-pull cannulas were placed bilaterally into the AH/PO region of anesthetized, paralyzed and ventilated rats. Perfusion of ...

The adrenoceptor blocking properties and hypotensive effects of the alpha-1 blocking agents urapidil and prazosin were compared in conscious instrumented rats. Both urapidil and prazosin in i.v. doses of 3 and 6 mg/kg and 0.125 and 0.25 mg/kg, respectively, blocked the pressor response to the alpha-1 adrenoceptor agonist phenylephrine. The ...

Morphine is generally regarded as having a centrally mediated depressant effect upon the cardiovascular system. We report here that in chronically instrumented conscious dogs, morphine produces a biphasic response; heart rate and mean arterial pressure initially increase followed by a reduction to below baseline levels. Differential inhibition by naloxone (NAL) ...

To test the hypothesis that the hypotensive action of urapidil is in part related to a direct action on the brain, the central (intracerebroventricular) and peripheral (intravenous) effects of urapidil were studied and compared with those obtained with clonidine and prazosin. All studies were conducted in conscious, chronically instrumented stroke-prone ...

In anesthetized and conscious domestic hens i.v. injections of LTC4 (1 and 3 micrograms/hen) and LTD4 (0.1-10 micrograms/hen) induced a pronounced hypotension, initially interrupted by a small, upward pressure deflection. No significant changes in HR, ECG-characteristics, or hematocrit were observed. It is concluded that neither plasma leakage nor myocardial ischemia ...