Changes in carbonic anhydrase may be the initial step of altered metabolism in hypertension.

Carbonic anhydrase (CA) is a well characterized pH regulatory enzyme in most of the tissues in the body. Changes in activities of CA have been associated with altered metabolism, especially in diabetes mellitus. Insulin resistance and hyperinsulinemia are common in hypertension. To investigate the possible role of CA, we measured the CA activity spectrophotometrically using p-nitrophenyl acetate as a substrate and acetazolamide, the specific inhibitor, in erythrocytes from normotensive and essential hypertensive subjects. Further, to evaluate the insulin action on CA, we used two different hemolysates; (i) insulin applied into hemolysate and (ii) hemolysate from insulin treated erythrocytes in vitro before the determination of CA activity. Two different levels of CA activities were obtained in these patients. CA activities were much lower (mean +/- SD, 0.88 +/- 0.19 U/min/mL) and higher (mean +/- SD, 1.77 +/- 0.23 U/min/mL) in patients than the normotensive controls (mean +/- 1 SD, 1.41 +/- 0.1 U/min/mL). These differences in both the groups were statistically significant (p less than 0.001). Similarly, total esterase activities in patients were (1.41 +/- 0.27 U/min/mL) that was 30% less in low activity group and (2.47 +/- 0.25 U/min/mL) that was 22% more in higher activity group in comparison with those from normotensives (2.02 +/- 0.17 U/min/mL). The relative percent of CA activities of insulin treated erythrocytes from normotensives and hypertensives were 11% and 18% higher than without insulin (p less than 0.05). No difference was observed when insulin was applied in the hemolysate. We conclude that essential hypertensive patients are associated with altered CA activity.(ABSTRACT TRUNCATED AT 250 WORDS)