Heat acclimation: role of norepinephrine in the anterior hypothalamus.
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.
D000064:Acclimatization; D000818:Animals; D001833:Body Temperature Regulation; D002851:Chromatography, High Pressure Liquid; D004298:Dopamine / Q000032:analysis; D006358:Hot Temperature; D007032:Hypothalamus, Anterior / Q000032:analysis / Q000502:physiology*; D008297:Male; D008734:Methoxyhydroxyphenylglycol / Q000031:analogs & derivatives / Q000032:analysis; D009638:Norepinephrine / Q000032:analysis / Q000502:physiology*; D005082:Physical Exertion; D011301:Preoptic Area / Q000032:analysis; D051381:Rats; D011919:Rats, Inbred Strains
D008734:Methoxyhydroxyphenylglycol; C010117:3,4-dihydroxyphenylglycol; D004298:Dopamine; D009638:Norepinephrine