Atrial natriuretic peptide (ANP) response during acute saline loading and its relationship to changes in blood pressure (BP) and sodium excretion were studied in 21 patients with essential hypertension (EH) and nine normotensive volunteers. Following 2 liters of isotonic saline infusion at a rate of 500 mL/hour, plasma ANP concentrations in patients with EH increased significantly from 69.9 +/- 6.0 (mean +/- SEM) to 103.6 +/- 17.1 pg/mL (p < 0.05) in the first hour and peaked at the second hour. In normal subjects, the increase in plasma ANP was not significant until the third hour of infusion (64.6 +/- 6.2 to 82.0 +/- 7.5 pg/mL, p < 0.05). Mean BP (MBP) remained stable and the natriuretic responses were similar in the two groups. However, hypertensive patients with a prompt rise in ANP during the initial two hours of infusion (fast responders) maintained a BP balance more efficiently than those with a delayed rise in ANP (slow responders), as the latter displayed a significant increase in MBP two hours after saline loading (126 +/- 5 to 133 +/- 5 mmHg, p < 0.05). Fast responders also had a greater percent of suppression of plasma aldosterone (-49.7 +/- 9.2 vs 15.9 +/- 42.0%, p = 0.05) one hour after saline loading, and a higher increment of natriuresis (263.9 +/- 43.8 vs 97.5 +/- 27.4%, p < 0.025) in the second hour of infusion than slow responders. Our results indicate that during acute saline loading, patients with EH have a faster and greater rise in plasma ANP than normotensives.(ABSTRACT TRUNCATED AT 250 WORDS)