Insulin resistance and hypertension in Japanese

In this article, some of our findings of epidemiologic and clinical studies on the actual state of insulin resistance in hypertension occurring in Japanese were described. In epidemiologic studies, a high prevalence of concomitant hypertension and impaired glucose tolerance was observed, and a significant positive correlation was found between blood pressure and blood glucose levels, even at a low degree, in two towns, the agricultural districts of Hokkaido. In clinical studies, insulin sensitivity, which was measured as M-values by the euglycemic hyperinsulinemic glucose clamp method, was significantly lower in essential hypertensives than in normotensive subjects. Moreover, this suppression of insulin sensitivity was also observed in young normotensive subjects with an apparent family history of hypertension, preceding the manifestation of hypertension. At the same time, obesity and aging were definitely correlated to the decrease in insulin sensitivity. On the assumed criterion that the normal range of M-values is mean +/- 1 SD of non-obese, non-diabetic young normotensive subjects, the prevalence of individuals with lowered M-value, which means existence of insulin resistance, was calculated as 45.4% in essential hypertensives and as 16.3% in normotensive subjects in this study. Increases in plasma norepinephrine levels and plasma renin activity, and decreases in urinary excretion of sodium and fractional excretion of sodium were observed during hyperinsulinemia produced by glucose clamp test. These responses to hyperinsulinemia were not different from those in normotensive subjects and, therefore, not specific to essential hypertensives. From these results, it was concluded that insulin resistance definitely exists among Japanese essential hypertensives, and that it plays an important role in the pathophysiology of essential hypertension.