Osmotic and Nonosmotic Control of Vasopressin Release in the Elderly: Effect of Metoclopramide

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Abstract
The study was undertaken to define the relationships between the arginine vasopressin (AVP) response to a pressure-volume stimulus (upright posture test), an osmolar challenge, and metclopramide injection (20 mg, iv) in normal young and elderly subjects. Besides confirming previous findings of increased AVP responsiveness to osmolar challenge and reduced AVP responsiveness to upright posture in the elderly, we found that metoclopramide stimulated AVP release in both young [from 1.09 .+-. 0.05 (mean .+-. SD) to 1.77 .+-. 0.05 pmol/L; P < 0.05] and elderly subjects from (1.54 .+-. 0.18 to 4.73 .+-. 1.82 pmol/L; P < 0.01). The response was much greater in the elderly (P < 0.01). The AVP responses to upright posture and metoclopramide were inversely correlated (r = -0.77; P < 0.01), suggesting that the elderly have increased sensitivity to stimuli, such as metoclopramide, to counteract their reduced sensitivity to baroreceptor stimulation of AVP release.