1. Responses of adrenomedullin to acute and chronic salt loading were examined in normotensive and hypertensive subjects.
2. In the acute salt load study, isotonic saline (50 ml/kg for 1 h) was intravenously infused into nine normotensive subjects and 11 patients with essential hypertension. Plasma adrenomedullin was higher in hypertensive than in normotensive subjects but was unchanged by saline infusion in either the normotensive (before infusion, 2.4 ± 0.2 fmol/ml; after infusion, 2.4±0.1 fmol/ml) or hypertensive (before infusion, 3.0±0.1 fmol/ml; after infusion, 2.9 ± 0.2 fmol/ml) group, while renin was suppressed and atrial natriuretic peptide was markedly increased. Plasma endothelin was not affected either.
3. In the chronic salt load study, seven normotensive subjects and 23 patients with essential hypertension underwent two 7-day periods of 30 and 260 mmol/day sodium intake. Depending on the blood pressure change, 13 hypertensive subjects were classified as salt-resistant and 10 as salt-sensitive. Salt-sensitive hypertensive subjects had suppressed plasma renin activity even during low salt intake. Plasma adrenomedullin or endothelin were not affected by the salt intake changes in any group; however, the high salt intake increased atrial natriuretic peptide in all groups.
4. These data indicate that the circulating level of adrenomedullin is not changed by either acute or chronic salt loading in normotensive subjects and patients with essential hypertension.