AJP - Regulatory, Integrative and Comparative Physiology, Vol 244, Issue 6 850-R856, Copyright © 1983 by American Physiological Society
Inappropriate drinking and secretion of vasopressin after caval constriction in dogs
T. N. Thrasher, M. Moore-Gillon, C. E. Wade, L. C. Keil and D. J. Ramsay
The object of this study was to determine if chronic thoracic vena caval
constriction affected mechanisms regulating water balance, independent of
known changes in sodium metabolism in the dog. Fluid and electrolyte
balances were determined for 5 days before and 14 days after constriction
of the vena cava (n = 5) and in a separate population of time controls (n =
4). Cardiac output was reduced and heart rate was increased in response to
chronic caval constriction although blood pressure was maintained at
control levels. Water intake and plasma arginine vasopressin (AVP)
increased from 31 +/- 4 ml/kg and 1.3 +/- 0.2 pg/ml during the control
period to 81 +/- 6 ml/kg and 3.4 +/- 0.6 pg/ml during the period of caval
constriction. The caval dogs developed a positive water balance, which
preceded the development of a positive sodium balance. This led to a
significant fall in plasma osmolality from a control mean of 296 +/- 1 to
284 +/- 4 mosmol/kg during caval constriction and dilutional hyponatremia.
Plasma and blood volume increased significantly in response to constriction
and were accompanied by formation of 123 +/- 10 ml/kg of ascitic fluid.
These results show that water intake and plasma levels of AVP were
increased in spite of a fall in plasma osmolality and an increase in
vascular volume. These responses cannot be secondary to sodium retention
because water was retained in excess of sodium hence hyponatremia.
Therefore, chronic caval constriction causes a profound primary disturbance
in mechanisms regulating water balance, which may contribute to the
formation of edema fluid.
