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

In this review, postulated passive and active fluxes of sodium, potassium, and calcium across the sarcolemma of the normal vascular smooth muscle cell are first summarized. Some practical problems encountered in their measurement are also mentioned. The review then considers how these fluxes appear to be altered in various forms of hypertension in animals and humans. Emphasis is given to abnormal fluxes of sodium and potassium due to altered sodium pump activity and permeability. Increasing evidence indicates that sodium retention due to increased sodium intake or decreased sodium excretion causes hypertension by releasing a humoral pressor substance from brain. This substance, which may be the putative natriuretic hormone, inhibits Na+, K+-ATPase and sodium pump activities in blood vessels and heart, thereby increasing contractile activity. In the genetic models of hypertension, the primary defect appears to be increased permeability of the vascular smooth muscle cell wall to sodium; pump activity increases to compensate for the increased inward leak of sodium. This may also be the case in patients with heritable essential hypertension. The possible consequences of super-imposing the sodium pump inhibitor on the primary defect are also considered. This may occur when animals with genetic hypertension or patients with heritable essential hypertension retain sodium subsequent to increased sodium intake and/or decreased ability to excrete sodium. Such superimposition should raise intracellular sodium concentration to high levels since now the pump would not fully compensate for the increased inward leak of sodium.
Hypertension
PMID:Abnormalities of membrane transport in hypertension. 636 Aug 83

It has been postulated that depressed membrane sodium transport is a necessary step in blood pressure elevation in essential hypertension. Accordingly, leucocyte sodium efflux-rate constants were estimated in 14 normotensive subjects who had one or more first-degree relatives with essential hypertension, and also in 14 matched control subjects with no such family history, before and after taking bendrofluazide for 7 days. Efflux rates in the controls did not change after the diuretic. However, in the relatives, mean total sodium efflux-rate constant was at first significantly depressed but later rose to normal with the diuretic. This was due almost entirely to an increase in glycoside-sensitive sodium pump activity. Blood pressure remained unchanged in both groups. Thus, assuming that perturbations in leucocytes reflect similar abnormalities in other cell lines, major changes in sodium transport in the normotensive individual without accompanying changes in blood pressure suggest that, while these changes may be a marker for later hypertension, they do not participate directly in blood pressure control.
Hypertension
PMID:Changes in leucocyte sodium transport in normotensive relatives of hypertensive subjects. Dissociation from blood pressure. 637 43

Leucocyte sodium efflux rate constants and intracellular electrolyte contents were estimated in 13 patients with untreated essential hypertension. There was no correlation between intracellular sodium or potassium content or efflux rate constant and blood pressure. The patients were then treated with oral nifedipine and blood pressure controlled. Sodium efflux rate constants and electrolyte contents were estimated one and three months after the start of treatment. There was a significant fall in blood pressure, but mean sodium efflux rate constant and intracellular sodium content were unchanged. There was no correlation between the fall in blood pressure, initial sodium efflux, or intracellular sodium content. These data do not support the hypothesis that the sodium pump and intracellular sodium content have a direct role in generating raised blood pressure, or that treatment of hypertension with calcium antagonists corrects a fundamental alteration of calcium-sodium exchange across the cell membrane.
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PMID:Calcium antagonists in hypertension: relation to abnormal sodium transport. 641 34

Leucocytes were isolated from venous blood of 11 normotensive volunteers with no family history of hypertension and the sodium efflux rate constants determined both alone and in the presence of increasing physiological concentrations of noradrenaline. There was a significant dose dependent reduction of total sodium efflux rate constant due to a reduction in ouabain sensitive sodium pump activity, glycoside insensitive efflux rate constants being unaffected. The magnitude of this effect was similar to the reduction in leucocyte sodium efflux rate constants observed in hypertensive patients (and their normotensive relatives). The noradrenaline induced depression of sodium pump activity was prevented by propranolol in a further seven experiments, suggesting that the effect was mediated by beta adrenoceptors. Catecholamines possibly functioning as circulating inhibitors of sodium transport may contribute to some of the disturbances in membrane electrolyte handling both in essential hypertension in man and in some experimental models of hypertension.
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PMID:Noradrenaline: a circulating inhibitor of sodium transport. 643 58

We studied changes in intracellular electrolytes and the rate constant of 22Na efflux from isolated leucocytes in Chinese patients with essential hypertension and their normotensive offsprings. The hypertensives had an increase of sodium content and a reduction of the total or ouabain-sensitive 22Na efflux from leucocytes. The normotensives born of hypertensive parents showed lower sodium content, higher potassium content and reduced rate constant of ouabain-insensitive 22Na efflux from leucocytes. The results suggest that the inhibition of cell sodium pump activity may be a marker of essential hypertension. Abnormal cell sodium transport observed in normotensives with family history of hypertension may have some etiological linking with the inheritance of hypertension.
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PMID:Abnormal leucocyte sodium transport in Chinese patients with essential hypertension and their normotensive offsprings. 653 3

The effect of local infusion of ouabain into the forearm vascular bed has been examined in 15 normotensive male volunteers in an attempt to define the nature of the functional abnormalities of the resistance vessels in primary hypertension. Ouabain and other drugs were infused into the brachial artery and forearm blood flow was measured by venous occlusion plethysmography. Infusion of ouabain at 2 micrograms/min for 1 h caused a 26% reduction in forearm blood flow with a small rise in systemic arterial pressure; the increase in vascular resistance was unaffected by prior treatment with phentolamine. After infusion of ouabain the dilator response to potassium was reduced by 33% but the responses to verapamil and sodium nitroprusside were unchanged. The results show that acute depression of sodium pump activity by ouabain reproduces the increased resting resistance and impaired response to potassium that are seen in hypertension. It does not reproduce the relative enhancement of responsiveness to verapamil that is also observed in the resistance vessels of patients with hypertension and this abnormality must have some other cause.
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PMID:Effect of local infusion of ouabain on human forearm vascular resistance and on response to potassium, verapamil and sodium nitroprusside. 668 Oct 36

The dilator response to local infusion of K+ has been assessed in the forearm resistance vessels of 17 men with primary hypertension and 11 controls, by using a standard plethysmographic method. The response to infusion of K+ at 0.1 mmol/min was smaller in the patients with hypertension than in the normal controls (P less than 0.03). The results are consistent with the view that the activity of the sodium pump is depressed in the resistance vessels of patients with hypertension, but they yield no evidence as to whether or not this abnormality contributes to the elevation of the peripheral resistance.
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PMID:The dilator response to K+ is reduced in the forearm resistance vessels of men with primary hypertension. 669 57

Several laboratories have reported evidence suggesting abnormalities in the activity of the sarcolemmal sodium pump in vascular smooth muscle in hypertension. The present experiments were designed to investigate the relationship of such changes to the status of the renin-angiotensin-aldosterone system and body fluid volumes. We assessed sodium pump activity in vitro in sodium-loaded tail artery and thoracic aorta freshly excised from rats with chronic one-kidney, one clip, and two-kidney, one clip hypertension, and from appropriate normotensive control rats. 86Rb uptake in the absence (total uptake) and presence of 1.0 mM ouabain (ouabain-insensitive uptake) was measured, and ouabain-sensitive uptake (nmole/mg dry weight/18 min) was calculated. There were increases in plasma renin activity in the two-kidney, one clip rats only. In the hypertensive rats there were significant increases (up to +60%) in the ouabain-sensitive and total 86Rb uptakes in both tail artery and aorta. The magnitude of increases in arterial tissue uptakes in the two forms of Goldblatt hypertension, and in one-kidney, one clip hypertensive rats given 0.9% saline to drink for 2 to 3 days before sacrifice, were similar. Further sodium loading of aortas from normotensive control rats did not increase their uptake. The results of this study provide no evidence for decreases in sodium pump activity, instead indicating that there are increases in the activity of the pump in the sarcolemma or arterial smooth muscle studied in vitro. These increases in pump activity do not appear to be related to altered activity of the renin-angiotensin-aldosterone system, to changes in body fluid volumes, or to increases in intracellular concentrations of sodium. Increases in numbers or concentration of sarcolemmal pump molecules or in their turnover rate may be involved. However, in vitro 86Rb uptake by tail artery and aorta may not reflect the status of sodium pump activity in resistance vessels in vivo.
Hypertension
PMID:Sodium pump activity in arteries of rats with Goldblatt hypertension. 703 34

One may postulate a genetic defect in membrane permeability, in the transport of sodium, or in the sodium pump in vascular muscle which could account for increased intracellular sodium and enhanced vascular contractility. If the electrogenic sodium pump is overactive, as in SHR, its inhibition may lead to significant depolarization and greater contraction. Sympathetic innervation may be essential for the development of membrane abnormality as well as for the development of hypertrophic vascular changes, both of which augment contraction and vascular tone. A similar membrane defect at the sensory endings of arterial stretch receptors may account for impaired arterial baroreceptor reflexes seen in very early phases of hypertension or, in some genetic models, before hypertension develops. This defect may be related to the sodium pump or sodium transport in the receptor region and cause a decrease in baroreceptor discharge and in the strain-sensitivity of the baroreceptors, resulting in exaggerated sympathetic drive. Further information is needed on the baroreflex control of various efferents in hypertension. Another membrane defect at the adrenergic nerve terminals may facilitate release of endogenous NE. Excessive salt intake may unmask or exaggerate the membrane defects. In the central nervous system a defect in glutamine, NE, or GABA receptors may contribute to a high central sympathetic drive. Greater receptor affinity to various pressor neuropeptides such as angiotensin and leucine enkephalin or greater release of these peptides may also account for the excessive CNS sympathetic activation or impairment of baroreflexes at a central level. Cardiac receptors may have a variable influence on sympathetic drive in the various stages of hypertension, depending on the degree of cardiac hypertrophy or cardiac size. Finally, increased renal afferent nerve activity may provoke an increase in sympathetic activity and provide a link between natriuretic factors and the sympathetic nervous system in hypertension.
Hypertension
PMID:The sympathetic system in hypertension. State-of-the-art review. 704 Feb 39

Alterations in vascular ionic metabolism preceded the onset of elevated blood pressure in the aldosterone-treated rat. Increases in 42K+ and 36Cl- turnover in the aorta and femoral artery were detected as early as 1 wk after the start of aldosterone infusion. These vascular changes were completely reversed after a 3-wk recovery period. An increased sensitivity to the effect of norepinephrine (NE) on aortic 42K+ turnover was also observed prior to a significant rise in systolic blood pressure. Enhanced sodium transport was also found in vessels from hypertensive rats infused with aldosterone for 4 wk. The potassium-sensitive component of the 24Na+ efflux was significantly elevated in vessels from hypertensives. This increase in sodium pump activity appeared to compensate for an increase in passive membrane permeability to sodium in that cell sodium levels were not altered by aldosterone treatment. A more rapid increase in 42K+ turnover occurred in aorta from aldosterone-treated rats when extracellular calcium was removed. Therefore, an impaired ability of calcium-dependent processes to adequately stabilize the vascular smooth muscle membrane may contribute to altered vascular ion transport. It is concluded that altered vascular electrolyte metabolism is an important pathogenic mechanism in the development of aldosterone-induced hypertension in the rat.
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PMID:Altered arterial ion transport and its reversal in aldosterone hypertensive rat. 714 45


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