Association of insulin resistance with salt sensitivity and nocturnal fallof blood pressure

Insulin resistance was demonstrated in hypertensive patients and in salt-se nsitive subjects. It was recently reported that the salt-sensitive state wa s related to a reduced fall in blood pressure during the night in essential hypertension. In the present study, the relationship among insulin sensiti vity, blood pressure response to salt intake, and nocturnal fall in blood p ressure was examined in 20 subjects with nondiabetic and nonobese essential hypertension during a low-salt and a high-salt diet. The subjects were mai ntained on a low-salt diet (50 mmol/d) and a high-salt diet (255 mmol/d) fo r 1 week each, in random order. On the sixth day of each diet, blood pressu re was measured every hour for 24 hours with an automatic device. Insulin s ensitivity was measured according to the steady-state plasma glucose (SSPGS ) method on the seventh day of each diet. Salt-induced increase in blood pr essure, which we defined as the change in 24-hour mean arterial pressure be tween the low and the high dietary salt intakes, was significantly correlat ed with SSPG (r = 0.60, P<0.01) during the high-salt period. There was a si gnificant negative correlation (r = -0.61, P<0.01) between SSPG and a noctu rnal Fall in mean arterial pressure during the high-salt period. Salt-induc ed increase in blood pressure was inversely correlated with a nocturnal Fal l in mean arterial pressure (r = -0.52, P<0.02) with the high-salt diet. Th ese results suggest that insulin resistance, salt sensitivity, and failed n octurnal fall in blood pressure are associated with each other in subjects with essential hypertension.