LONG-TERM EFFECT OF NIFEDIPINE AND HYDROCHLOROTHIAZIDE ON BLOOD-PRESSURE AND SODIUM HOMEOSTASIS AT VARYING LEVELS OF SALT INTAKE IN MILDLY HYPERTENSIVE PATIENTS

To elucidate and compare the effects of nifedipine (NIF) and hydrochlorothiazide (HCTZ) on blood pressure (BP) and sodium (Na) balance, we conducted a randomized, double-blind, crossover study with 50 mg/day HCTZ and 90 mg/day NIF (as the sustained-release gastrointestinal therapeutic system preparation) in 10 mildly hypertensive patients over approximately 8 weeks. Prior to treatment, the subjects were brought into balance at an intake of 150 mmol/day. During treatment, Na intake was lowered and raised to 50 and 300 mmol/day, respectively, in random order. Then, the subjects were brought into balance on treatment at a level of 150 mmol/day. Balance observations were made during and after the drugs were discontinued. Both HCTZ and NIF lowered BP similarly. When Na intake was lowered from 150 to 50 mmol/day, a significant decrease in diastolic BP was observed with HCTZ. Increasing Na intake to 300 mmol/day did not affect BP. At an intake of 150 mmol/day, HCTZ caused prompt natriuresis, with a negative balance of 150 mmol by 3 days. No initial natriuresis could be shown with NIF. Decreasing Na intake to 50 mmol/day caused prompt negative Na balance with both drugs; increasing it to 300 mmol/day was associated with + 150 mmol Na balance with HCTZ while no significant increase was seen with NIF. Discontinuing both drugs caused prompt increase in BP and Na retention over 6 days, which was not different for the drugs. Plasma renin activity (PRA) increased with HCTZ but not with NIF. Further, changing Na intake affected PRA with HCTZ. With NIF, PRA appeared to be uncoupled from the effects of dietary Na intake. In contrast to HCTZ, no adverse metabolic effects were observed with NIF. The data suggest that NIF results in chronic mild natriuresis similar in magnitude to HCTZ. The PRA appears inactivated, although not lowered. The effects of NIF on BP may be at least in part related to the natriuresis and blunting of PRA. The BP-lowering effects of NIF are less dependent upon NaCl intake than those of HCTZ.