THE EFFECTS OF ENALAPRIL ON THE NATRIURETIC RESPONSE EVOKED BY AN ORAL SODIUM LOAD IN SODIUM DEPRIVED NORMOTENSIVE AND HYPERTENSIVE RATS

Previous studies have shown that an oral sodium load during sodium dep rivation is excreted faster than an intravenous load. We wanted to stu dy whether the renin-angiotensin-aldosterone system might be associate d with this phenomenon and therefore the influence of the angiotensin converting enzyme (ACE) inhibitor enalapril was investigated. The expe riments were performed on four strains of rat: spontaneously hypertens ive rats (SHR), Wistar-Kyoto (WKY) rats, inbred hypertension-prone (SS /Jr) and hypertension-resistant (SR/Jr) Dahl rats. In SHR and WKY rats pretreated with enalapril it was observed that an intravenous sodium load induced a renal sodium excretion which was between two and five t imes larger than that seen after an oral load. In SR/Jr and SS/Jr rats the sodium excretion was the same regardless of the route of administ ration. in SS/Jr rats sodium excretion increased three- to fourfold up on sodium repletion, whereas no significant increase was observed in S R/Jr rats. Thus, the present results indicate that an intact renin-ang iotensin system is necessary for the interplay between the gastrointes tinal tract and kidney.