AJP - Regulatory, Integrative and Comparative Physiology, Vol 258, Issue 4 827-R835, Copyright © 1990 by American Physiological Society
Altered sensitivity of osmotically stimulated vasopressin release in quadriplegic subjects
B. M. Wall, H. H. Williams, D. N. Presley, J. T. Crofton, E. G. Schneider, L. Share and C. R. Cooke
Nephrology Section, Veterans Administration Medical Center, Memphis, Tennessee 38104.
Osmoregulation of vasopressin release was studied in 15 quadriplegic
subjects (Quad) and 7 healthy control subjects (Con). Hypertonic NaCl (0.85
M) was infused intravenously (0.05 ml.kg-1.min-1) over 90 min in studies on
supine subjects and in comparable studies on the same subjects erect
(sitting). Erect posture in Quad, but not in Con, was accompanied by
orthostatic reductions in arterial blood pressure and by significantly
increased plasma aldosterone (P less than 0.001) and cortisol (P less than
0.001) concentrations and increased plasma renin activity (P less than
0.025). Changes in plasma arginine vasopressin concentration (PAVP) during
hypertonic NaCl infusions were also greater in erect than in supine Quad (P
less than 0.005), despite identical changes in plasma osmolality (Posm).
Linear regression analysis of the PAVP/Posm relationship during hypertonic
NaCl infusions showed highly significant correlations (P less than 0.0002)
in both Quad and Con. Mean slope values for regression lines, however, were
significantly higher in erect than in supine Quad (P less than 0.005) but
did not differ in relation to posture in Con. Differences in posture were
not associated with differences in abscissal intercepts in either Quad or
Con. These studies show significant alterations in the sensitivity of
osmotically stimulated vasopressin release related to differences in
posture in Quad, characterized by enhanced sensitivity in erect posture due
to nonosmotic stimuli not evident in Con.
