Erythrocyte water, Na+-K+ cotransport, and forearm vascular function in humans.

We examined the relationships between erythrocyte (RBC) composition (Na+, K+, and water content) and ouabain-insensitive transports (Na+-K+ cotransport, Li+-Na+ countertransport) and forearm vascular hemodynamics under standardized basal conditions and during vasoconstriction (intra-arterial infusion of graded doses of norepinephrine and angiotensin II) and vasodilation (intra-arterial phentolamine and postischemic exercise). RBC water content correlated positively and significantly (r = 0.53, p = 0.001) with minimum forearm vascular resistance, a measure of vascular structural change, and negatively with maximal forearm blood flow (r = -0.55, p less than 0.001). Similar correlations with forearm vascular resistance and blood flow were observed under all experimental conditions. RBC Na+-K+ cotransport correlated positively and significantly (r = 0.43, p = 0.01) with the change in forearm blood flow produced by phentolamine, a functional measure of alpha-adrenergic tone, and was as strong an independent predictor of phentolamine-induced blood flow change as was arterial norepinephrine concentration. RBC Na+-K+ cotransport was also significantly positively correlated with residual forearm blood flow and resistance after phentolamine administration, where nonadrenergic influences predominate. RBC water correlated negatively with Li+-Na+ countertransport (r = -0.33, p less than 0.05) and Na+-K+ cotransport (r = -0.44, p less than 0.01). We propose that RBC water is a marker for a vascular structural property that contributes to vascular reactivity. RBC Na+-K+ cotransport seems to relate most strongly to the sympathetically mediated control of forearm blood flow and may also be linked to the intrinsic myogenic tone of the forearm vasculature.(ABSTRACT TRUNCATED AT 250 WORDS)