Genetic polymorphism of Na-K cotransport in essential hypertension

Erythrocyte Na-K cotransport is high and genetically correlated to hypertension in Milan hypertensive strain (MHS) rats. In man there is a substantial overlap of individual values between essential hypertensives and controls. However, the findings in rat strains with different types of genetic hypertension suggest that Na-K cotransport studies may throw light on the different pathogenetic mechanisms of the human disease. In 28 normotensive and 22 hypertensive families the midparent-offspring correlation of Na-K cotransport values was significant only in hypertensive families (r = 0.48) and not significant in normotensive ones (r = 0.06), indicating genetic polymorphism for its phenotypic expression only in the hypertensives. In 189 essential hypertensives and 109 normotensives carefully selected from a population-based screening in order to exclude uneven sampling bias, analysis for the bimodality of the distribution of Na-K cotransport clearly showed that normotensives are distributed unimodally and hypertensives bimodally, with nadir of the distributions at about 450 mumols (1 RBC/h). Dividing the hypertensives according to Na-K cotransport value, the high Na-K cotransport subgroup has lower fractional percent excretion of uric acid and plasma renin activity. These data suggest that the high Na-K cotransport subgroup has peculiar characteristics of greater proximal tubular reabsorption (lower fractional excretion of uric acid) that may cause body volume expansion (lower plasma renin activity).