Cardiovascular drugs and serum uric acid.

Uric acid (UA) is the final product of purine catabolism in man, and it is excreted mainly by the kidneys when renal function is not impaired. Consequently, serum (S) UA increases as a function of purine intake, and it varies inversely to uricosuria. The latter variable diminishes in response to low-sodium intakes and vice versa. Insofar as the diet is not usually controlled in studies in which the response of SUA to drugs is evaluated, most reports are to be considered cautiously. Common diuretics elevate SUA in healthy subjects, hypertensives and patients with heart failure, apparently by elevating net UA reabsorption in the nephronal proximal tubule. This drug action, which becomes noticeable shortly after the institution of treatment and remains throughout it, starts at low doses (e.g., 12.5 mg hydrochlorothiazide or 1.25 mg bendrofluazide once daily in subjects with uncomplicated hypertension) and increases in dose-dependent fashion. Beta-blockers tend to elevate SUA. The angiotensin-converting enzyme (ACE) inhibitors captopril, enalapril and ramipril have been found to increase uricosuria mildly, likely by lowering the net reabsorption of UA in the proximal tubule. These three drugs and lisinopril can blunt the rise in SUA provoked by diuretics in hypertensives if used at sufficiently high doses relative to the dose of the diuretic. The angiotensin II antagonist losartan augments uricosuria mildly and thereby decreases SUA. The cardiovascular implications of the response of SUA to drugs remain speculative. Uric acid can scavenge various reactive oxygen species and thus reduce oxidative stress, which seems to contribute to the development and/or progress of various cardiovascular conditions, including hypertension, atherosclerosis and heart failure. Consequently, it may be theorised that the elevations in SUA induced by diuretics might contribute to the established favourable action of these agents on cardiovascular prognosis. Conversely, diuretic-induced increases in SUA are to be considered detrimental according to an old hypothesis that maintains that SUA is a cardiovascular risk factor; this construct is largely based upon the results of selected epidemiological undertakings. The cardiovascular implications of the effects of drugs on SUA, if any, should be elucidated through purposive research.