Journal of Applied Physiology, Vol 58, Issue 6 1923-1928, Copyright © 1985 by American Physiological Society
Heat acclimation: role of norepinephrine in the anterior hypothalamus
J. V. Christman and C. V. Gisolfi
The hypothesis that anterior hypothalamic (AH) sensitivity to
norepinephrine (NE) is altered by chronic exercise in the heat was tested
in male Sprague-Dawley rats. Treadmill exercise 6 days/wk for 3 wk at 21
m/min was performed at 23 degrees C (control; C) or at 35 degrees C (heat
acclimated; HA), progressing from 20 to 50 min/day in 2 wk. Time for core
temperature (Tco) to rise from 39.5 to 40.5 degrees C during a
heat-tolerance test after conditioning increased (P less than 0.05) in the
HA group. To test for a change in AH sensitivity, the change in Tco to 2-,
5-, 10-, 20-, and 40-micrograms doses of NE injected bilaterally into the
AH was determined after conditioning. Dose-response regression lines showed
that exercise in the heat increased the slope and shifted the Tco-NE dose
relation to the left. In a separate series of experiments on 6
sedentary(s), 10 C, and 10 HA animals, the amounts of NE, dopamine, and
3,4-dihydroxyphenylglycol (DOPEG) were determined by high-pressure liquid
chromatography in the AH, median preoptic area (PO), cortex, and cerebellum
after 9 wk of conditioning. Results showed that in the PO there was a
significant increase in NE and DOPEG in the HA vs. C group and a trend of
increasing NE from the S to C to HA groups. The data indicate that exercise
in the heat increases NE-induced peripheral heat-dissipating capacity and
increases catecholamine storage in the PO.
