ARGININE-VASOPRESSIN AND OSMOLALITY IN THE ELDERLY

Objectives: To evaluate the influence of age on plasma arginine vasopr essin (AVP) concentrations and the relationship between plasma AVP and serum osmolality in younger and older subjects, and in the elderly, t o assess the effect of gender on plasma AVP concentration and to deter mine the impact of prostaglandin blockade on renal responsiveness to A VP. Design: Cross-sectional study; randomized, double-blind, crossover , placebo-controlled study. Setting: The Renal Laboratory, Royal North Shore Hospital (younger adults) and Clinical Room, St Vincents Hospit al (elderly subjects). Participants: 45 younger adults (35 +/- 9 years ) and 41 elderly subjects (29 males, 12 females; 78 +/- 3 years). All subjects were healthy and non-institutionalized. The elderly subjects were screened to exclude significant pathology (clinical assessment, m ultiple investigations). Intervention: Blood samples were drawn from a ll younger and elderly subjects. The elderly subjects were randomly al located indomethacin or placebo for 1 month. Following a 1 to 2-week w ashout, the alternative was administered for a further 1 month. Main O utcome Measures: Plasma AVP and serum osmolality and plasma AVP, serum , and urine osmolality at baseline were measured on indomethacin and p lacebo. Results: In the elderly subjects, baseline plasma AVP concentr ation was significantly higher than in the younger subjects studied (4 .7 +/- 0.7 vs 2.1 +/- 0.2 pg/mL respectively; P = 0.0003). Plasma AVP was strongly correlated with serum osmolality in the younger subjects (r = 0.76, P = 0.0001) but not in the elderly cohort (r = -0.18, P = 0 .26). No difference was found between the sexes in plasma AVP (P = 0.8 9), and indomethacin treatment did not alter the plasma AVP/urine osmo lality ratio (P = 0.85) in the elderly subjects. In addition, changes in plasma AVP with indomethacin therapy did not correlate with changes in serum osmolality (r = 0.16, P 0.09). Conclusions: Aging is accompa nied by an increase in plasma AVP concentrations. In healthy, elderly subjects, plasma AVP is not dependent on serum osmolality and is not i nfluenced by gender. Indomethacin has no effect on the renal responsiv eness to plasma AVP.