AJP - Regulatory, Integrative and Comparative Physiology, Vol 251, Issue 3 621-R626, Copyright © 1986 by American Physiological Society
Volume influences on thirst and vasopressin secretion in dehydrated sheep
R. G. Park, M. Congiu, D. A. Denton and M. J. McKinley
The contribution of extracellular fluid volume (ECFV) to water consumption
and plasma vasopressin concentration (PAVP) after water deprivation for 52
h was examined in sheep. Intravenous infusion of isotonic NaCl, equivalent
to either estimated ECFV loss or total body water loss, significantly
reduced water intake by 37% when water was offered 3 h after infusion but
not when water was offered 1 h after infusion. Plasma osmolality (POsm) was
reduced after 3 h. Infusion of 200 mM NaCl, which maintained POsm,
decreased water consumption by the same degree as isotonic NaCl infusion.
Thus large decreases in POsm had no effect on water intake in this
experimental protocol. Lack of inhibition of drinking 1 h after infusion
suggests that the decrease observed after 3 h may have been mediated by
receptors in the interstitial fluid (ISF) compartment and not the
intravascular compartment. PAVP was reduced 3 h after infusion of NaCl but
not at 1 or 2 h after infusion. POsm was also decreased at 3 h. Thus
reduction of PAVP by NaCl infusion may have been caused by either ISF or
intracellular fluid volume expansion.
