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Query: UMLS:C0020538 (hypertension)
 170,190 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

In an open, non-comparative study, the effect of Prazosin, a selective and competitive inhibitor of alpha-adrenergic receptors, on blood pressure and lipid metabolism was studied in out-patients with hypertension. The pronounced antihypertensive effect of this vasodilator was confirmed. In almost all patients, i.e. in 144 of 171 patients with monotherapy, Prazosin caused a significant decrease of diastolic blood pressure within 3 to 6 weeks (in sitting position reduction to values below 90 mm Hg). This confirms the established antihypertensive effect due to vasodilation. In addition, Prazosin therapy is associated with a significant reduction in total cholesterol (p less than 0.001), a significant increase of HDL-cholesterol (p less than 0.001), a significant reduction of triglycerides (p less than 0.01) during the study period of 26 weeks. Prazosin monotherapy had a more pronounced influence on serum lipids than the combination of Prazosin with a diuretic. Prazosin was tolerated well; only during the first treatment weeks, a higher frequency of side effects due to abrupt reduction of blood pressure was observed, closely correlating with a too rapid increase of daily dose. Due to its proven antihypertensive effect and its favorous influence on lipid metabolism, Prazosin is suited for long-term treatment of hypertension, thus reducing two major risk factors, associated with coronary heart disease.
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PMID:[Prazosin in the treatment of hypertension: effect on lipid metabolism]. 343 87

Increasing awareness of the hazards of diuretic therapy has cast doubt on the appropriateness of its uniform use as initial treatment for hypertension. To establish the relative efficacy and acceptability of alternative forms of initial therapy, prazosin and hydrochlorothiazide were prospectively compared. In a one-year study, 62 patients with a diastolic blood pressure greater than or equal to 100 mm Hg were randomly allocated to receive one of the two agents. Twenty of 32 (63 percent) patients receiving prazosin and 17 of 30 (57 percent) receiving hydrochlorothiazide satisfied the year-long study requirements. For the most part, the dropout rate was not drug related. The percentages of subjects completing the study with the initial drug, without addition of a second drug, were identical in both groups (prazosin: 10 of 32 [31 percent] and hydrochlorothiazide: nine of 30 [30 percent]). In both treatment groups, blood pressure declined similarly and significantly (p less than 0.001) by the end of the study. The blood pressure of subjects receiving prazosin decreased from 150.3/105.8 mm Hg to 135.3/90.3 mm Hg, whereas the blood pressure of subjects receiving hydrochlorothiazide declined from 147.3/103.8 to 130.0/89.1 mm Hg. A reduction in diastolic blood pressure to less than 95 mm Hg was achieved in 80.0 percent of patients started with prazosin and in 78.6 percent of those started with hydrochlorothiazide. A further reduction to less than 90 mm Hg was achieved in 45.0 and 64.3 percent, respectively (not significant). Patients who completed the study with single-drug therapy in both treatment groups showed nonsignificant decreases in mean potassium levels from initial to final readings when compared with baseline readings (prazosin: 0.21 meq; hydrochlorothiazide: 0.41 meq). However, patients receiving prazosin had 11.5 percent of their readings less than or equal to 4.0 meq, whereas those receiving hydrochlorothiazide had 38.1 percent of their readings similarly distributed (p less than 0.05). Furthermore, four patients receiving hydrochlorothiazide had potassium levels less than or equal to 3.5 meq; none of those receiving prazosin had levels in that range. At baseline, no patient in the study had potassium levels of less than 4.0 meq. Prazosin-treated patients whose initial fasting blood glucose was less than 110 mg/dl had 3.7 percent (one of 27) of subsequent measurements greater than or equal to 110 mg/dl. These abnormal levels were found 18.2 percent (six of 33) (not significant) of the time in similar hydrochlorothiazide-treated subjects. Symptomatic side effects were primarily mild and transient in those receiving either drug alone.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Initial antihypertensive therapy. Comparison of prazosin and hydrochlorothiazide. 351 91

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 maintenance of hypertension in this disease. We have investigated this possibility in New England Deaconess Hospital rats harboring a transplantable pheochromocytoma that secretes norepinephrine and dopamine. Both clonidine and chlorisondamine, a ganglionic blocker, markedly decreased blood pressure in tumor-bearing rats. However, in other rats made acutely hypertensive with a norepinephrine infusion, neither clonidine nor chlorisondamine decreased blood pressure. This result indicates that in an acute model of hypertension, where baroreflex mechanisms have likely withdrawn sympathetic tone, neither clonidine nor chlorisondamine had nonspecific antihypertensive effects. A central nervous system site of action for the antihypertensive effect of clonidine in the rats harboring pheochromocytoma was suggested by the observation that the opiate antagonist naloxone both reversed and prevented clonidine's effect on blood pressure. Prazosin and yohimbine were utilized to determine the respective contributions of alpha-1 and alpha-2 adrenergic receptors in the maintenance of hypertension in rats harboring pheochromocytoma. Both drugs markedly lowered blood pressure in these rats. Our data suggest that both the sympathetic nervous system and circulating catecholamines are involved in the maintenance of hypertension due to pheochromocytoma.
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PMID:Role of the sympathetic nervous system in the maintenance of hypertension in rats harboring pheochromocytoma. 359 6

The centrally mediated cardiovascular changes induced by clonidine were studied in conscious rats. Clonidine administered intracerebroventricularly (i.c.v.), and intravenously (i.v.) caused hypotension following an initial pressor response. I.v. clonidine caused significant greater hypotension than i.c.v. clonidine (30 micrograms/kg; p less than 0.05). With the 30 micrograms/kg i.c.v. dose, a tachycardia was observed in all rats following initial transient bradycardia. No tachycardia was observed when clonidine was administered i.v. Propranolol (3 mg/kg i.v.) did not modify the cardiovascular actions of i.c.v. clonidine except initial pressure response. While combined treatment with propranolol (3 mg/kg i.v.) and atropine (1 mg/kg i.v.) abolished both the bradycardic and tachycardic actions of i.c.v. clonidine (30 micrograms/kg), but did not modulate the hypotensive action. Yohimbine (30 micrograms/kg i.c.v.) converted the hypotension induced by i.c.v. clonidine (30 micrograms/kg) to hypertension, attenuated the bradycardia but did not modulate the tachycardia. The same dose of i.c.v. yohimbine attenuated the hypotensive effect of i.v. clonidine (30 micrograms/kg) but did not affect the initial pressor response. Prazosin (30 micrograms/kg i.c.v.) did not modulate either phase of the heart rate response to i.c.v. clonidine. These results provide evidence of centrally mediated pressor and tachycardic actions of clonidine in conscious rats. The tachycardia appears to be mediated through the inhibition of parasympathetic tone and is not dependent on alpha-adrenoceptor mechanism. In conscious rats the opposing influence of centrally mediated pressor and depressor actions may result in the apparently low hypotensive potency of i.c.v. clonidine.
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PMID:Tachycardic and hypertensive effects of centrally administered clonidine in conscious rats. 372 2

Selective alpha 1 antagonists decrease blood pressure by reducing elevated peripheral resistance and preserving normal cardiac reflexes. They have also been reported to usually decrease total cholesterol and low-density lipoprotein cholesterol levels, and, in some studies, to increase high-density lipoprotein cholesterol levels. Prazosin, a quinazoline derivative, is well tolerated and is not associated with chronic toxicity. Prazosin has been successfully used in the treatment of hypertension for more than 10 years. Its short plasma half-life requires twice-daily dosing. Although the hypotensive response to an initial dose of prazosin is usually greater than to subsequent doses during long-term therapy, the initial response is an accurate predictor of the hypotensive response in patients during long-term therapy. The vasodilatory action of prazosin is largely due to its blockade of vascular postjunctional alpha 1 receptors. The mechanism involved in its effect on lipid levels is currently under investigation and is an important consideration since hypercholesterolemia, as well as hypertension, is an independent risk factor for stroke and coronary heart disease. Reduction of blood pressure with conventional agents, such as beta blockers or diuretics, has not had the expected impact on coronary heart disease. However, since alpha 1 blockers may influence both hemodynamics and lipids, they warrant evaluation as first-line treatment of hypertension to confirm that they also have an effect on coronary heart disease.
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PMID:Clinical pharmacology of selective alpha blockers. Hemodynamics and effects on lipid levels. 379 97

The antihypertensive effects of the alpha-adrenergic blocking agent prazosin have been studied extensively. Prazosin exerts a vasodilatory effect via selective competitive blockade of post-junctional alpha 1 adrenoceptors. Results of various other clinical trials suggest that the selective alpha 1-adrenoceptor antagonist prazosin has a significant impact on two of the three primary coronary heart disease risk factors. In the articles reviewed herein, prazosin is shown to be an effective agent when used alone or in combination with other agents. Stamler and co-workers showed that prazosin alone achieves successful control of blood pressure equal to that of hydrochlorothiazide. Inouye et al compared the effectiveness of prazosin with propranolol and hydrochlorothiazide and found all three drugs to be comparable. Okun reveals the efficacy of prazosin across the spectrum of hypertension--mild, moderate, and severe. Additionally, Okun's prazosin versus captopril study revealed equal efficacy between these two drugs. The long-term comparative data of Lowenstein and Neusy show prazosin and atenolol to be equally effective as monotherapy after one year.
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PMID:Alpha blockade. An overview of efficacy data. 379 99

Antihypertensive therapy significantly reduces cardiovascular morbidity and mortality in the rapidly growing population of elderly patients. However, the desire to treat more of these patients is dampened by the concern that a reduction in blood pressure may compromise cerebral blood flow, causing untoward consequences. This study evaluated the therapeutic effect of titrated doses of prazosin, an alpha-adrenergic blocking agent, on systemic blood pressure and cerebral blood flow in elderly patients with chronic stable hypertension. Prazosin alone or co-administered with hydrochlorothiazide significantly lowered mean systolic and diastolic blood pressures in 31 elderly hypertensive patients. At the same time, however, there was no significant change in cerebral blood flow, which was measured in eight patients. Neither harmful biochemical changes nor treatment-related adverse effects were observed in any patients. Prazosin therapy alone or in combination with low-dose diuretic therapy was effective in the treatment of hypertension in this elderly population. Furthermore, blood pressure reduction with prazosin therapy was accomplished without compromising cerebral blood flow and without unfavorably altering lipid profiles.
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PMID:Antihypertensive therapy in the elderly. Effects on blood pressure and cerebral blood flow. 379 2

Prazosin is a selective alpha 1-adrenoceptor antagonist which is useful alone or in combination for the treatment of hypertension and heart failure. Unlike many other antihypertensive drugs, the action of prazosin appears to be closely related to its concentration in plasma or whole blood. Prazosin is variably absorbed, is subject to first-pass metabolism, and is eliminated almost entirely as metabolites of much lower hypotensive activity than the parent drug. Prazosin is highly bound to plasma and tissue proteins. The influences of renal, hepatic and cardiac disease on the disposition of prazosin are reviewed, as are the effects of pregnancy and ageing. The optimum use of prazosin in clinical practice depends on an understanding of the pharmacokinetic properties of the drug.
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PMID:Clinical pharmacokinetics of prazosin--1985. 388 89

The treatments of mild hypertension with atenolol and prazosin in occupationally active men and women were compared in a double blind cross-over with placebo. The hypotensive effect of the beta-adreno-receptor blocking drug, atenolol, were striking and in accordance with current knowledge, using one daily dose of 100 mg. In contrast, the hypotensive effect of taking 2 mg prazosin twice a day was modest, averaging about 3% when compared with placebo, somewhat less but still detectable during the performance of muscular exercises. Atenolol medication significantly reduced heart rate and blood pressure responses to muscular exercises, covering a range of work loads experienced during ordinary working days. No increased feeling of muscular fatigue or other discomfort during muscular work compared to that on prazosin and placebo medication could be detected. It was therefore concluded that atenolol medication was a useful treatment of mild hypertension and did not reduce the normal working ability and exercise tolerance. Prazosin medication did not significantly change working ability and exercise tolerance.
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PMID:Working ability and exercise tolerance during treatment of mild hypertension. II. A comparison between atenolol and prazosin medication. 389 71

The effects of prazosin and alphamethyldopa on blood lipids and lipoproteins were assessed in 20 patients with mild or moderate arterial hypertension. Parameters measured included serum cholesterol (CHO), triglycerides (TG), high density lipoprotein-cholesterol (HDL-CHO), insulin (I), glucose (G), and non-esterified fatty acids (NEFA). Prazosin -4 mg/day for 6 weeks in hydrochlorothiazide-treated patients lowered blood pressure by 18.6/17.2 (systolic/diastolic pressure) mmHg. There was a significant decrease in CHO (-5.8%), in I (-16.5%), and in NEFA (-3.0%), and a significant increase in HDL-CHO (+15.5%). Alphamethyldopa 250-750 mg/day for 6 weeks in hydrochlorothiazide-treated patients lowered blood pressure by 18.8/14.6 (systolic/diastolic pressure) mmHg, accompanied by a non-significant decrease in CHO and TG, and significant increases in HDL-CHO (+10.3%), G (+8.5%) and NEFA (+6.4%). Thus, prazosin appears to have a more beneficial effect on blood lipids and lipoproteins than alphamethyldopa.
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PMID:Effects of prazosin and alphamethyldopa on blood lipids and lipoproteins in hypertensive patients. 389 72


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