COMPARISON OF CYCLIC GUANOSINE-MONOPHOSPHATE RESPONSE TO INFUSION OF ATRIAL-NATRIURETIC-PEPTIDE IN YOUNG AND ELDERLY SUBJECTS

Objective: To compare the sensitivity to atrial natriuretic peptide (A NP) in young and elderly subjects. Design: Double-blind, random-order, placebo-controlled study using two different rates of ANP infusion. S ubjects: Eight healthy young (23 +/- 3 years, mean +/- SD) and eight h ealthy elderly (76 +/- 4 years) subjects recruited from the general po pulation. Measurement: Plasma cyclic guanosine monophosphate (cGMP, th e second messenger of ANP) levels reflecting the sensitivity of biolog ically active ANP receptors. Results: Baseline ANP levels were higher and rose to a greater extent in the elderly both during low- (0.25 mug /min) and high-dose (2.0 mug/min) infusion of ANP. Plasma levels of cG MP rose in proportion to the increase in ANP. When the rise in cGMP le vels was related to the increase in ANP levels (expressed as nmol/L pe r 100 pg/mL ANP increase), no difference was found between young and e lderly subjects. Conclusion: The ability of elderly subjects to increa se cGMP in response to exogenous ANP is similar to that of young subje cts. This may reflect a similar sensitivity of the target organs towar ds ANP. However, because of lower clearance in the elderly, a similar dose of ANP results in a greater elevation of ANP and cGMP levels and hence induces a greater effect.