Dietary sodium regulation of alpha 2-adrenoceptors in Sabra hypertensive (SHB) and normotensive (SBN) rats.

Cerebral and renal alpha 2-adrenoceptors, modulated in vitro by sodium ions, are implicated in the control of sympathetic activity and of sodium reabsorption, respectively. The aim of the present study was to investigate the effect of high (8%) versus normal (0.2%) sodium diet on cerebral and renal alpha-adrenoceptors of Sabra hypertensive (SBH) and normotensive (SBN) rats. After two or five weeks of high sodium diet alpha 2-adrenoceptor density was increased in the renal cortex of SHB and SBN rats. In contrast, cerebral alpha 2-adrenoceptor densities were markedly decreased in SBN but unchanged in SBH rats. Blood pressure increased only after five weeks of high sodium diet, in SBH and to a lesser extent in SBN rats. The change in alpha 2-adrenoceptor densities thus preceded the blood pressure elevation. The dietary sodium-induced increase in renal alpha 2-adrenoceptor densities which precedes the blood pressure elevation does not appear to be a genetic marker of hypertension. Conversely, the marked decrease of cerebral alpha 2-adrenoceptors in SBN rats may represent an adaptative change in sympathetic activity responsible for the resistance to the development of salt-induced hypertension.