NA+ LI+ AND NA+/H+ COUNTERTRANSPORT ACTIVITY IN HYPERTENSIVE NON-INSULIN-DEPENDENT DIABETIC-PATIENTS - ROLE OF INSULIN-RESISTANCE AND ANTIHYPERTENSIVE TREATMENT/

We measured erythrocyte Na+/Li+ and Na+/H+ countertransport: (CT) acti vity (millimoles per liter per cell per hour) in 10 healthy control su bjects (age, 38 +/- 4 years; body mass index, 25 +/- 1 kg/m(2)) and in 26 hypertensive patients with non-insulin-dependent diabetes mellitus ([NIDDM] age, 49 +/- 3 years; body mass index, 29 +/- 1 kg/m(2); fast ing plasma glucose, 157 +/- 12 mg/dL) 4 weeks after discontinuation of previous antihypertensive treatment. Na+/Li+ CT was significantly inc reased in hypertensive NIDDM patients compared with controls (0.56 +/- 0.04 v 0.30 +/- 0.03, P < .01), whereas Na+/H+ CT was similar to cont rol levels (21 +/- 1 v 20 +/- 2). A positive correlation was found bet ween Na+/H+ CT and the severity of insulin resistance (r = .69, P < .0 1), mean arterial pressure ([MAP] r = .64, P < .01), plasma triglyceri de concentration (r = .46, P < .05), and plasma total cholesterol (r = .41, P < .05). An inverse correlation was found between Na+/Li+ CT ac tivity and plasma insulin concentration (r = -.47, P < .05). No relati onship was observed between Na+/Li+ CT activity and either creatinine clearance or proteinuria. Stepwise multiple regression analysis for al l metabolic variables and blood pressure showed that only the severity of insulin resistance was positively correlated with increased Na+/Li + CT activity. Na+/H+ and Na+/Li+ CT activity were not altered by 3 ho urs of euglycemic physiologic hyperinsulinemia (84 +/- 3 mu U/mL). Hyp ertensive NIDDM subjects were treated for 3 months with captopril, nif edipine, or doxazosin. After captopril, a reduction of Na+/H+ CT was o bserved (22 +/- 4 v 13 +/- 2, P < .05): Na+/Li+ CT decreased after dox azosin (0.56 +/- 0.06 v 0.45 +/- 0.05, P < .05) and nifedipine (0.52 /- 0.06 v 0.42 +/- 0.05, P < .05). In conclusion, in hypertensive NIDD M subjects, (1) Na+/Li+ CT is increased and is correlated with the lev el of insulin resistance and the MAP; (21 acute physiologic hyperinsul inemia does not affect Na+/Li+ or Na+/H+ CT activity; and (3) Na+/H+ C T activity is reduced by captopril, and Na+/Li+ CT is decreased by dox azosin and nifedipine. Copyright (C) 1997 by W.B. Saunders Company.