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

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

The effectiveness and safety of transdermally administered clonidine hydrochloride was assessed in 16 patients with type-II diabetes mellitus. This group of patients was chosen because of the frequent occurrence of hypertension in diabetic patients and potential problems with transdermal absorption of medication because of small vessel disease. A skin patch containing clonidine hydrochloride (Catapres TTS) was applied at weekly intervals after an appropriate placebo lead-in period. Satisfactory response to therapy was seen in 15 of the 16 patients. One patient developed a generalized skin rash and was withdrawn from the study. Correlation between change in diastolic blood pressure and plasma clonidine levels was noted. Of note was the absence of the usual side effects (drowsiness, dry mouth, etc.) seen with oral clonidine administration. This study thus highlights the success of transdermal clonidine therapy in controlling blood pressure in the mild hypertensive patient with diabetes mellitus.
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PMID:The use of transcutaneous clonidine hydrochloride in the patient with diabetes mellitus and mild hypertension. 383

Twenty patients aged 60-74 years entered a study on the effect of transdermal clonidine (Catapres-TTS) as monotherapy for mild hypertension [diastolic blood pressure (DBP) 90-104 mmHg]. Seventeen patients (85%) had a positive therapeutic response (DBP reduced to less than 90 mmHg or by greater than or equal to 5 mmHg). Patient acceptance was high and side effects mild; however, one-quarter of the patients experienced localized skin reactions. A slight increase in fasting plasma glucose level (mean delta = 20 mg/dl) was consistently observed. Transdermal clonidine led to a sustained decline in plasma catecholamine levels although this effect did not seem to be closely related to the observed decreases in blood pressure. Three out of four evaluable patients had a blood pressure 'overshoot' upon discontinuation of therapy to levels above pretreatment values. Transdermal clonidine appears to be effective and generally well tolerated in the treatment of mild hypertension in the elderly; however, more studies designed to investigate effects on glucose tolerance and the possible existence of a rebound syndrome are needed.
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PMID:Transdermal clonidine therapy in elderly mild hypertensives: effects on blood pressure, plasma norepinephrine and fasting plasma glucose. 386 15

Acetylcholine in the central nervous system appears to be involved in some aspects of hypertension. Clonidine and methyldopa may inhibit acetylcholine (Ach) release in several brain areas. The present study was therefore designed to determine whether a depletion of brain Ach could modify the antihypertensive effect of clonidine in freely moving spontaneously hypertensive (SHR), Grollman hypertensive (GHR) and DOCA-salt hypertensive (DHR) rats. Intravenous injection of clonidine (15, 30 and 75 micrograms/kg) reduced mean arterial pressure (MAP) and heart rate (HR) in all hypertensive animals. The hypotensive effect was more marked in SHR than in DHR and GHR. The effect was also reproducible when the drug dose was repeated 3 h later in rats pretreated with saline (5 microliters) in the lateral cerebral ventricle (i.c.v.). When clonidine administration was repeated in hypertensive animals 3 h after i.c.v. hemicholinium-3 (20 micrograms/5 microliters), the decrease in MAP and HR was significantly reduced compared with that observed in the same animals after the first injection. The data suggest that the antihypertensive effect of clonidine depends partially upon the integrity of central cholinergic neurons.
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PMID:Role of brain cholinergic system in the antihypertensive effect of clonidine in different models of rat hypertension. 386 18

The antihypertensive effects of urapidil and clonidine have been studied in a double-blind cross-over trial in 11 hypertensive outpatients with mild to moderate hypertension, at rest and during isometric exercise. Urapidil 30 mg b.i.d. significantly decreased the standing diastolic blood pressure (p less than 0.05) and the systolic blood pressure at the end of isometric exercise (p less than 0.05). Clonidine 0.075-0.15 mg b.i.d. was more effective in decreasing both systolic and diastolic blood pressure in the supine and standing positions as well as during isometric work (p less than 0.05-0.001). Urapidil caused fewer side-effects than clonidine. Overall, in the doses used urapidil had a weaker antihypertensive effect and caused fewer side-effects than clonidine.
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PMID:Antihypertensive effects of urapidil and clonidine: a double-blind cross-over study. 388

The pharmacology of central alpha-adrenoceptor-stimulating agents is discussed, with particular reference to clonidine (Catapres; Boehringer Ingelheim) and guanfacine (Estulic; Sandoz), and their haemodynamic effects are compared and contrasted. The main differences between the effects of clonidine and guanfacine on hypertension are: guanfacine activates presynaptic alpha-adrenoceptors 10 times more selectively than clonidine; guanfacine has an alpha 2/alpha 1-selectivity ration 25 times higher than clonidine; clonidine decreases cardiac output and guanfacine decreases peripheral resistance, clonidine has no effect on stroke volume but guanfacine increases it; and when the clonidine withdrawal syndrome in the spontaneously hypertensive rat is compared with cessation of guanfacine treatment at an equipotent antihypertensive dose, the withdrawal syndrome after guanfacine appears later and is much less severe. Guanfacine may be preferable to clonidine as a central alpha-adrenoceptor stimulant in the treatment of hypertension.
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PMID:Clonidine and guanfacine--comparison of their effects on haemodynamics in hypertension. 388 93

The putative role of the central nervous system in the maintenance of elevated blood pressure in patients with essential hypertension (EH) and renal hypertension [unilateral renal parenchymal disease (RPD) and unilateral renal artery stenosis (RAS)] was studied by investigating the cardiovascular and hormonal effects of the predominantly centrally acting sympatholytic agent, clonidine. Oral clonidine lowered blood pressure substantially in all three groups. Levels of plasma renin activity were unchanged in EH and RAS but progressively fell in RPD. Plasma noradrenaline levels fell in all three groups. Clonidine therefore reduced blood pressure to the same extent in three distinct groups of hypertensives, in two of which the initiating cause was undoubtedly renal. This indicates that, although the primary cause differed, a prominent factor sustaining hypertension may have been an increase or an inappropriate maintenance of central pressor mechanisms.
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PMID:Cardiovascular and hormonal effects of clonidine in patients with essential hypertension and renal hypertension. 391 57

Clonidine withdrawal syndrome is described in a patient with heart failure and suspected cardiogenic shock. Hemodynamic monitoring disclosed hypertension and a very high systemic vascular resistance. Treatment consisted of nitroprusside followed by captopril.
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PMID:Clonidine withdrawal syndrome in a patient with heart failure. 398 25

By isolating young rats (90-100 g) a state of hypertension and tachycardia was induced after 7 days or a longer period of social deprivation. Clonidine, a drug used to treat hypertension in man, readily reversed the high blood pressure and heart rate in this experimental model of hypertension. In two different tests, an elevated nociceptive threshold was shown to be present in isolated animals as compared to group-housed rats. Naloxone was found to reverse this hypoalgesic state. The opiate antagonist also diminished the high blood pressure in the socially-deprived animals. Moreover, after 7 days of isolation, 24 hr of housing the rats in groups of five made the level of blood pressure and the sensitivity to pain return to control values. In this experimental model, in which hypertension was linked to stressful housing conditions, the data suggest that high blood pressure and hypoalgesia are closely associated.
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PMID:Association between hypoalgesia and hypertension in rats after short-term isolation. 399 Sep 18

Clonidine, in a daily dosage of 0.15-4.8 mg., effectively lowered systolic and diastolic pressures in 26 out of 28 impatients with moderate to severe hypertension, including five with primary renal disease. The action of the drug did not depend on posture and was not associated with reduction in renal function. Side-effects were not severe, but mental changes occurred in four patients.Clonidine is a useful alternative to currently available antihypertensive drugs, but further evaluation of its longterm efficacy is required.
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PMID:Treatment of hypertension with clonidine. 545 24


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