HYPOTENSIVE RESPONSE TO ATRIAL-NATRIURETIC-PEPTIDE ADMINISTRATION IS ENHANCED WITH AGE

Background. Plasma levels of atrial natriuretic peptide (ANP) increase with age. To test the hypothesis that the cardiovascular response to ANP is age dependent and to examine the role of the increased levels o f ANP in the hypotensive response to orthostatic challenge, we compare d the hemodynamic response of young and elderly subjects to ANP infusi on and orthostatic challenge. Methods. Blood pressure, heart rate, for earm cutaneous resistance, plasma ANP, and plasma norepinephrine were measured in the supine position and following upright tilt before and after a 60-minute infusion of atrial natriuretic peptide (0.05 mu g/kg /min) in 7 young (27 +/- 4 years) and 5 elderly (74 +/- 4 years) normo tensive, healthy subjects. Results. Prior to ANP infusion, the respons e to upright tilt was similar in both groups. Infusion of ANP produced similar steady state plasma levels of ANP in both groups (young: 435 +/- 49 pg/ml; elderly: 429 +/- 32 pg/ml). Supine systolic blood pressu re decreased by 4 +/- 2 mmHg in the young subjects and by 18 +/- 8 mmH g in the elderly subjects after infusion P < .08). In contrast, change s in supine heart rate, forearm cutaneous resistance, and plasma norep inephrine were similar in both groups (Delta heart rate: young + 5 +/- 3 beats/min, elderly + 4 +/- 2 beats/min; Delta forearm cutaneous res istance: young-38 +/- 9%, elderly - 40 +/- 6%; Delta norepinephrine: y oung + 55 +/- 11%, elderly: + 43 +/- 13%). ANP infusion abolished the vasoconstrictor response normally associated with orthostatic challeng e in both groups, despite a significant release of catecholemines and an enhanced heart rate response. This resulted in significant systolic blood pressure reduction in both young (- 7 +/- 2 mmHg, p < .05) and elderly subjects (- 16 +/- 4 mmHg, p < .05). The drop in systolic bloo d pressure in response to upright tilt and ANP infusion was four times larger in the elderly subjects (change from pre-ANP level: young - 8 +/- 3 mmHg, elderly - 32 +/- 5 mmHg, p < .005).