Renin, Angiotensin, Sodium and Organ Damage

Abstract

Angiotensin II and sodium balance affect the status of each other and both--either separately or together--can lead to an increase in blood pressure. They also can cause vascular and cardiac damage due to direct effects and effects mediated by the blood pressure increase. This paper reviews the important interactions among these three variables. Acute blood pressure elevation during sleeping but not during waking hours causes cardiac hypertrophy in rats. Similarly, lowering of blood pressure with an angiotension converting enzyme (ACE) inhibitor during sleep but not when awake causes regression of cardiac hypertrophy in rats with 2kidney (K)-1clip (C) Goldblatt hypertension. If angiotensin is given to rats on a low (0.4%) NaCl diet, blood pressure rises but there is less cardiac hypertrophy. Cardiac hypertrophy is greatest after angiotensin administration in rats on a high (4%) NaCl diet. In both the 2K-1C and 1K-1C Goldblatt models, a high salt intake reduces the blood pressure lowering effect of captopril and losartan and prevents regression of cardiac hypertrophy. Combined administration of an ACE inhibitor and an angiotensin type 1 (AT1) receptor blocker to rats on a low (0.2%) NaCl diet produces a syndrome that leads to death with cardiac involution. All features of the syndrome are reversed or prevented by 4% NaCl intake. It is hypothesised that the interaction between angiotensin II and sodium intake can be explained by differences in the way protons produced by contracting cells are neutralized. The sodium hydrogen exchanger and the sodium 2 bicarbonate cotransporter are stimulated by the AT1 and angiotensin type 2 (AT2) receptor, respectively. If the ratio of receptors is altered in favour of the AT2 receptor, then less cardiac hypertrophy will result from the same workload. Review of the clinical literature reveals that many of these results in rats have correlations in clinical medicine. Thus high night time blood pressure is associated with a greater morbidity and high salt intake causes cardiac hypertrophy and vascular stiffness independent of blood pressure levels. When deciding on treatment in human hypertension these results have important clinical implications.