Effect of treatment with hydrochlorothiazide on the red cell Na,K-adenosine triphosphatase in men with hypertension.

We studied the effect of hydrochlorothiazide, 50 mg daily, on Na,K-adenosine triphosphatase (ATPase) activity in the red cells of 10 black men with hypertension. We also examined net sodium and potassium movement in sodium-loaded, potassium-depleted, red cells. Treatment with hydrochlorothiazide resulted in a significant increase in mean ouabain-sensitive ATPase activity (+/- SEM) from 118.4 +/- 14.6 to 158.1 +/- 15.3 nmol phosphate released per milligram of protein (P = 0.0004). Ouabain-resistant ATPase did not change. Net sodium extrusion rose significantly, from 1.62 +/- 0.27 to 2.32 +/- 0.33 mmol/L/hr (P = 0.0275). We postulate that the enhanced activity of the Na,K pump results from the volume contraction induced by the diuretic. This interpretation is consistent with the concept that the Na,K pump is inhibited in volume expansion and volume-expanded hypertension. The finding of enhanced pump activity in subjects given treatment with hydrochlorothiazide suggests a possible mechanism of the antihypertensive action of diuretic therapy.