RESPONSES OF NATRIURETIC PEPTIDES TO ACUTE AND CHRONIC SALT LOADING IN NORMOTENSIVE AND HYPERTENSIVE SUBJECTS

Responses of endocrine systems to acute and chronic salt loading were examined in normotensive and hypertensive subjects. In the acute salt load study, isotonic saline (20 ml/kg for 1 h) was intravenously infus ed in 10 normotensive subjects and 12 patients with essential hyperten sion. Plasma noradrenaline was suppressed by saline infusion in the no rmotensive subjects (-19%, p < 0.05), but was not suppressed in the hy pertensive patients (-5%, NS). Plasma brain natriuretic peptide concen tration was significantly increased in the hypertensive patients (+15% , p < 0.05), while it was unchanged in the normotensive subjects, In t he chronic salt load study, 9 normotensive subjects and 30 patients wi th essential hypertension underwent two 7-d periods of 30 and 260 mmol /d sodium intake. On the basis of the blood pressure change, 17 hypert ensive patients were classified as salt-resistant and 13 as salt-sensi tive. The salt-sensitive hypertensive patients had suppressed plasma r enin activity even during low-salt intake. During high salt intake, th e plasma noradrenaline concentration failed to decrease in the salt-se nsitive hypertensive patients (-6%, NS), whereas it fell significantly in the normotensive subjects (-27%, p < 0.05) and the salt-resistant hypertensive patients (-33%, p < 0.01). The high-salt intake also incr eased plasma concentrations of brain natriuretic peptide as well as at rial natriuretic peptide in all groups. In the salt-sensitive hyperten sive patients, there was a positive correlation between the increase i n blood pressure and that in atrial natriuretic peptide (r = 0.84, p < 0.01), These data indicate that brain natriuretic peptide is involved in chronic changes in body fluid volume. In patients with essential h ypertension, acute volume expansion also evokes the response of brain natriuretic peptide. Salt-sensitive hypertension seems to be character ized by blunted response of the sympathetic nervous system, In additio n, an increase in atrial natriuretic peptide is likely to play an impo rtant role in mechanisms counteracting salt-induced elevation of blood pressure.