Journal of Applied Physiology, Vol 58, Issue 1 114-120, Copyright © 1985 by American Physiological Society
Effects of dehydration on the vasopressin response to immersion
H. von Ameln, M. Laniado, L. Rocker and K. A. Kirsch
Nine healthy volunteers underwent three experimental procedures in random
order. The protocols were 4 h of thermal dehydration followed by 2 h of
head-out water immersion, 4 h of thermal dehydration followed by 2 h of
chair rest, and 6 h of rest in the supine position. Four hours of heat
exposure (50 degrees C) resulted in a body weight loss of approximately
3.5%. Plasma osmolality rose by approximately 5 mosmol/kg, mean arterial
pressure (MAP) decreased from 85 to 78 mmHg, and body temperature increased
from 36.8 to 38.6 degrees C. As a consequence of the combined action of
hypertonicity, hypovolemia, hypotension, and hyperthermia, plasma arginine
vasopressin (AVP) increased from 2.1 to 8.1 pg/ml after 4 h thermal
dehydration. Changes in body weight, plasma osmolality, body temperature,
and MAP were similar after either a subsequent 2 h of water immersion or 2
h of chair rest. However, during chair rest plasma AVP remained elevated
(8.4 pg/ml), whereas during immersion plasma AVP decreased from 8.1 to 4.7
pg/ml. This was probably due to the central hypervolemia induced by
immersion. Our results support the hypothesis that central hypervolemia
rather than hypotonicity is the primary stimulus for AVP suppression during
water immersion in dehydrated subjects. During the early immersion period
hypoosmolality might contribute to the AVP suppression.
