AJP - Regulatory, Integrative and Comparative Physiology, Vol 245, Issue 6 860-R872, Copyright © 1983 by American Physiological Society
Influence of daily sodium intake on vasopressin secretion and drinking in dogs
A. W. Cowley Jr, M. M. Skelton, D. C. Merrill, E. W. Quillen Jr and S. J. Switzer
Studies were carried out to determine the relationship between daily sodium
intake, drinking, and vasopressin (AVP) secretion in normal conscious dogs.
Chronic responses to 5-day elevations of daily sodium intake (200 meq/day)
and 2-wk decreases in daily sodium intake (5 meq/day) were determined. Dogs
were studied with ad libitum drinking and with water intake restricted to
the amount drunk during the normal-sodium (30 meq/day) control period.
Although acute elevations of plasma AVP occurred after a normal (40 meq Na)
gastric load, chronic high-sodium intake resulted in no change of
steady-state plasma AVP levels or daily AVP excretion (UAVP) with ad
libitum drinking. Total water intake and frequency of drinking, however,
increased nearly fourfold. In the absence of excess drinking, plasma AVP
and UAVP both exhibited a nearly sixfold increase during the period of
high-sodium intake. Despite elevations of plasma AVP, daily urine volume
increased and urine osmolality rose only gradually during the 5 days of
high-sodium intake. Chronic low-sodium intake also did not alter plasma
AVP, but total water intake was reduced 20%. The data indicate that with
water available, extracellular osmolality is controlled predominantly by
drinking rather than by AVP secretion, that either osmolality or sodium
concentration is the predominant controller of drinking and AVP secretion,
and that daily water excretion need not be related directly to plasma AVP.
