Influence of age on cardiovascular effects of increased dietary sodium and angiotensin-converting enzyme inhibition in normotensive Wistar rats.

Abstract

Recent studies have shown that increased intake of dietary sodium chloride produces blood pressure-independent increase in cardiac and renal mass even in young normotensive rats. With advancing age the harmful cardiovascular effects of increased dietary sodium are not so well known. In the present study the influence of advancing age on the cardiovascular effects of increased intake of sodium (control diet, 0.3% and high-sodium diet, 2.6% sodium in the chow) were examined in young and aged (3 and 18 months old, respectively, at the beginning of the experiment) male normotensive Wistar rats in a six-week study. Moreover, the potential role of renin-angiotensin system in ageing during normal and a high-sodium intake was studied using a pharmacological tool, angiotensin converting enzyme (ACE) inhibitor ramipril. Ageing did not significantly modify basal systolic blood pressure measured by the tail cuff method. A high intake of sodium chloride increased blood pressure significantly only in aged rats, while in young rats it increased renal weight. Left ventricular weight was not affected by high-sodium diet in either age group. The ACE inhibition during control diet lowered blood pressure and decreased left ventricular weight in young rats only and these effects were completely blocked by a high-sodium diet. The maximal vascular contraction force of mesenteric arterial rings to noradrenaline was decreased with ageing while endothelium-dependent and -independent relaxation responses were unaltered with ageing. The sensitivity to sodium nitroprusside was impaired by the high-sodium diet in young rats. In both age groups the urinary excretion of calcium was increased during the high-sodium diet. In conclusion, the increased intake of sodium produced different changes in cardiovascular function in normotensive rats depending on age. With advancing age, the sensitivity to sodium-induced increase in blood pressure was increased. In aged rats a high intake of dietary sodium elevated blood pressure, while in young rats it increased renal mass without increase in blood pressure. In both age groups sodium did not affect left ventricular hypertrophy. Both high-sodium intake and ageing attenuated or even abolished the cardiovascular effects of ACF inhibition.