Cardiovascular and sympathoadrenal responses to heat stress
following water deprivation in rats.
Massett, Michael P., David G. Johnson, and Kevin C. Kregel.
Department of Exercise Science, University of Iowa, Iowa City, IA
52242; and Departments of Exercise and Sport Sciences, Physiology,
and Internal Medicine, University of Arizona, Tucson, Arizona,
87521
APStracts 2:0301R, 1995.
This study was designed to characterize the regional and systemic
hemodynamic and sympathoadrenal responses to heating following 24-
and 48-h of water deprivation in chloralose-anesthetized, male
Sprague-Dawley rats (n = 7 per group). Water deprivation produced
significant decreases in body weight of 8.1% and 13.7% in the 24-h
and 48-h groups (p < 0.05), respectively. Following water
deprivation, rats were exposed to an ambient temperature of 43
degrees C. After correcting for body weight differences, heating
rates were faster in the 48-h group compared to both euhydrated and
24-h groups. Mean arterial blood pressure (MAP), heart rate, colonic
(Tco) and tail (Ttail) temperatures increased above baseline in all
groups during heating. Renal and mesenteric artery blood flow
velocities decreased and vascular resistances increased in response
to heating. Compared to euhydrated controls, 48-h water-deprived rats
exhibited attenuated pressor (_ MAP = 36 +/- 3 mmHg vs. 18 +/- 3
mmHg) and visceral vasoconstrictor (%_ in mesenteric resistance =
122.6 +/- 27.3% vs. 54.9 +/- 6.9%) responses during heating. Tail
-skin blood flow estimated from Ttail was also lower at baseline and
the onset of heating in water-deprived rats. However, peak Ttail and
Tco values were similar across groups. Plasma catecholamines measured
in separate groups of rats (n = 6 per group) were significantly
higher at baseline and the end of heating in the 48-h group compared
to euhydrated and 24-h groups. Despite this exaggerated
sympathoadrenal response, the 48-h group exhibited attenuated
hemodynamic responses to nonexertional heating compared to euhydrated
and 24-h water-deprived rats. These data suggest that cardiovascular
and thermoregulatory adjustments can compensate for small changes in
hydration state (i.e., 24-h), but more severe levels of hypohydration
significantly alter blood pressure and body temperature regulation
during heat stress.
Received 14 November 1994; accepted in final form 17 November
1995.
APS Manuscript Number R655-4.
Article publication pending Am. J. Physiol. (Regulatory Integrative
Comp. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 30 November 95