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PubMedDate not supplied

[Effects of adrenergic stimulation on transmembrane transport of Na+ in patients with essential hypertension].

BACKGROUND: It has been studied whether an adrenergic stimulation induced by the cold pressor test (CPT) could influence the behaviour of the transmembrane transport systems of sodium in hypertensive subjects compared to a normotensive control population. MATERIALS AND METHODS: Twenty-two hypertensive subjects (average age 43.2 +/- 5.7 years), with normal weight, without signs of cardiovascular and metabolic diseases, underwent the cold pressor test. The dynamic behaviour of sodium erythrocytic transport systems and plasmatic norepinephrine was evaluated basally, at the third minute during the cold pressor test and 20 minutes after the end of the test. The same test was carried out in a control population made up of 20 normotensive subjects (average age 41.9 +/- 4.8 years), selected on the basis of the absence of any cardiovascular or metabolic pathology and without family history of arterial hypertension. RESULTS: The cold pressor test did not cause significant changes in the sodium transmembrane transport systems in normotensive subjects, while in the hypertensive subjects a significant reduction was observed, during the test, in the total efflux of sodium and in the sodium/potassium pump, respectively from 2636 +/- 296 mumol/l/red blood cells/hr to 2032 +/- 178 mumol/l/red blood cells/hr (p < 0.0001) and from 2156 +/- 149 mumol/l/red blood cells/hr to 1610 +/- 101 mumol/l/red blood cells/hr (p < 0.0001); the intraerythrocytic sodium increased from 6.5 +/- 1.0 mmol/l/cells to 7.2 +/- 1.1 mmol/l/cells (p < 0.04) and the passive permeability decreased from 0.039 +/- 0.004 hr-1 to 0.018 +/- 0.006 hr-1 (p < 0.0001). During cold pressor test the increase in the plasma norepinephrine levels was correlated to the reduction in the total efflux of sodium (r = -0.60; p < 0.003) and in the sodium/potassium pump (r = -0.59; p < 0.003) only in hypertensive subjects. CONCLUSIONS: Our data show that an adrenergic stimulation, induced by the cold pressor test, is able to significantly influence the behaviour of transmembrane fluxes of sodium in hypertensive subjects, and it causes an inhibitory effect on the sodium/potassium pump and an increase in the intraerythrocytic sodium. Such data show the existence in hypertensive subjects of an interrelationship between adrenergic activity and sodium transport systems that could cooperate in causing and/or in maintaining the hypertensive syndrome.

Adult↗

PubMedDate not supplied

[Effect of beta blockade on the erythrocyte transport of Na+: evaluation during stimulation by cold pressure test in patients with essential hypertension].

Several studies have shown in essential hypertension alterations of the transmembrane red blood cells sodium fluxes, as an involvement, especially in the early phases, also of the adrenergic system. In this study we evaluated the behaviour of red blood cells fluxes of sodium before, during and after the cold pressor test, a method used also to evoke an adrenergic stimulation, in twenty hypertensive subjects, 14 males and 6 females, with an average age of 43.2 +/- 5.7 years, with normal weight and without cardiovascular complications and metabolic diseases. The behaviour of the Na+ total efflux (Na+ TE), of the Na+/K+ pump, of the Na+K+ cotransport (Na+/K+ CT), of the Na+/Li+ counter transport (Na+/Li+ Cnt), of the Na+ passive permeability (Na+ PP), of the intracellular Na+ (I Na+) and of the plasmatic noradrenaline (NE) was evaluated basally, at the third minute during cold pressor test (CPT) and 20 minutes after the end of the test. The test, which the same method, was repeated after a 30 day treatment with propranolol at the dose of 240 mg/day in three daily administrations. The beta-blockade caused, besides the reduction of both the systolic and diastolic pressure values, a significant increase in the Na+/K+ CT (from 248 +/- 41 to 314 +/- 71 mmol/l/cells/h, p < 0.001) and a decrease in the Na+ PP (from 0.039 +/- 0.004 to 0.023 +/- 0.007 hr-1, p < 0.00001), probably directed towards the reduction of the accumulation of intracellular Na+, that could compete, among the other mechanisms, with the anti-hypertensive action of the beta-blockers. The CPT caused, before the beta-blockade, a significant depression of the Na+/K+ pump (from 2057 +/- 149 to 1610 +/- 101 mmol/l/cells/h, p < 0.00001) and of the Na+ TE (from 2640 +/- 397 to 2032 +/- 179 mmol/l/cells/h, p < 0.00001) inversely correlated to the levels of NE (r = -0.60, p < 0.003), with a consequent increase in I Na+ (from 6.2 +/- 0.6 to 7.5 +/- 1.5 mmol/l/cells, p < 0.001), showing how the adrenergic activation in hypertensive subjects is able to interfere with the systems of transmembrane transport with an inhibitory attitude, that is expressed by an increase in the levels of I Na+. The beta-blockade was able to outweigh the depression of the Na+/K+ pump (from 1843 +/- 584 to 1728 +/- 640 mmol/l/cells/h, p: ns) and the reduction of the Na+ TE, preventing the accumulation of I Na+ (from 6.3 +/- 1.6 to 6.6 +/- 1.3 mmol/l/cells, p: ns). Such data show an increased susceptibility of the Na+ transport systems to the adrenergic stimuli in hypertensive subjects with a tendency to favor the accumulation of I Na+ and that the beta-blockade is able to antagonize the effects, with a maintenance of the intracellular levels of Na+.

Adrenergic beta-Antagonists↗