Long term reduction in sodium balance: possible additional mechanism whereby nifedipine lowers blood pressure.
OBJECTIVE
To assess the changes in sodium excretion and sodium balance after withdrawal of long term nifedipine.


METHODS
Single blind, placebo controlled study in patients receiving fixed sodium and potassium intakes.


METHODS
Blood pressure unit of a teaching hospital in south London.


METHODS
Eight patients with mild to moderate uncomplicated essential hypertension who had been taking nifedipine 20 mg twice daily for at least six weeks.


METHODS
Withdrawal of nifedipine and replacement with matching placebo for one week.


METHODS
Urinary sodium excretion and cumulative sodium balance, body weight, plasma atrial natriuretic peptide concentrations, plasma renin activity and aldosterone concentrations, and blood pressure.


RESULTS
During nifedipine withdrawal there was a significant reduction in urinary sodium excretion (day 1: -62.7 mmol/24 h; 95% confidence interval -90.3 to -35.0) and each patient retained a mean of 146 (SEM 26) mmol sodium over the week of replacement with placebo. Body weight and plasma atrial natriuretic peptide concentrations increased during the placebo period and seemed to be associated with the amount of sodium retained. Systolic blood pressure rose from 157 (9) to 165 (9) mmHg (95% confidence interval of difference -7.1 to 22.1) when nifedipine was replaced with matching placebo, and the rise seemed to be related to the amount of sodium that was retained.


CONCLUSIONS
Nifedipine causes a long term reduction in sodium balance in patients with essential hypertension. This long term effect may contribute to the mechanism whereby nifedipine lowers blood pressure.
Pevahouse
J B
JB
Department of Medicine, St George's Hospital Medical School, London.
Markandu
N D
ND
Cappuccio
F P
FP
Buckley
M G
MG
Sagnella
G A
GA
MacGregor
G A
GA
D000328:Adult; D000368:Aged; D000450:Aldosterone / Q000097:blood; D009320:Atrial Natriuretic Factor / Q000097:blood; D001794:Blood Pressure; D001835:Body Weight; D005260:Female; D006801:Humans; D006973:Hypertension / Q000097:blood / Q000188:drug therapy / Q000378:metabolism* / Q000652:urine; D008297:Male; D008875:Middle Aged; D009543:Nifedipine / Q000627:therapeutic use*; D012083:Renin / Q000097:blood; D016037:Single-Blind Method; D012964:Sodium / Q000378:metabolism* / Q000652:urine
D000450:Aldosterone; D009320:Atrial Natriuretic Factor; D012964:Sodium; D012083:Renin; D009543:Nifedipine