Up-regulation of alpha 2 adrenoceptors and down-regulation of beta 2 adrenoceptors by high-salt diet in normotensive men: enhanced up-regulation of operative (alpha 2:beta 2) adrenoceptor ratio predicts salt sensitivity.

In 24 normotensive male volunteers (age 20-25 years) reduction of sodium intake from 200 to 50 mmol/day over 2 weeks resulted in a 14% fall of alpha 2-adrenoceptors of platelets from 209.5 to 179.4 fmol/mg (P less than 0.01) and in a 16% rise of beta 2-adrenoceptors of lymphocytes from 13.3 to 16.2 fmol/mg (P less than 0.05) which was reversible by 2 weeks of high sodium intake. In contrast to the comparatively minor changes of alpha 2- and beta 2-adrenoceptor density, the functionally probably more relevant 'operative (alpha 2:beta 2) adrenoceptor ratio' decreased by 53% from 22.9 to 14.9 (P less than 0.01) during the low-salt diet. Although neither the individual changes of alpha 2- and of beta 2-adrenoceptor densities correlated with individual blood pressure changes induced by variations in sodium intake, there was a highly significant positive correlation (r = 0.55, n = 33; P less than 0.01) between the rises of the 'operative adrenoceptor ratio' and the rises of blood pressure induced by high salt intake. We conclude that the 'operative adrenoceptor ratio', although only determined on alpha 2- and beta 2- and not on alpha 1- and beta 1-adrenoceptors, and only on circulating blood cells, may be representative for sympathetic resistance vessel tone, at least as a function of variations of salt intake. Enhanced up-regulation of the 'operative adrenoceptor ratio' in the salt-sensitive part of the population may be one important early step in the development of essential hypertension.