Endogenous digitalis-like factors in hypertension and chronic renal insufficiency

Endogenous digitalis-like factors have been implicated in the adaptations that accompany renal insufficiency and in the pathogenesis of hypertension. We recently described several fractions of normal human plasma that inhibit NaK-ATPase and exhibit apparent digoxin-like immunoreactivity. To determine if hypertension and/or renal insufficiency affect plasma levels of these factors, we examined four patient groups: normotensive controls; hypertensive subjects with normal renal function; hypertensives with moderate renal insufficiency; and chronic dialysis patients. Plasma levels of digoxin-like immunoreactivity and NaK-ATPase inhibitory activity were significantly increased in hypertensive patients with mild renal failure (7.6 +/- 1.1 ouabain equivalents, mean +/- SEM, N = 21 vs 4.1 +/- 1.1 in normotensive controls, N = 20, P less than 0.05). NaK-ATPase inhibitory activity tended to be higher in patients with primary hypertension and normal renal function (5.5 +/- 0.7 ouabain equivalents, P less than 0.07); in dialysis patients, it was not different from controls. There was no correlation between NaK-ATPase inhibitory activity and blood pressure in any group. There was a significant rise in plasma NaK-ATPase inhibitory activity during dialysis (+ 1.8 +/- 0.7 ouabain equivalents, N = 22, P less than 0.03). As we have found that NaK-ATPase inhibitory activity in the plasma of normal humans can be separated into three distinct fractions, EI1, EI2, and EI3, we analyzed the plasma of 10 dialysis patients further. The increase in NaK-ATPase inhibitory activity could be attributed to fractions EI1 and EI3. These results suggest that plasma NaK-ATPase inhibitors increase with chronic renal insufficiency, but not hypertension alone. Although hemodialysis may acutely raise plasma levels, long-term dialysis returns them to the normal range.