Previous studies have shown that heat acclimation raises the temperature threshold for heat-induced splanchnic vasoconstriction in the rat (W. Haddad and M. Horowitz. Thermal Balance in Health and Disease, Advances in Pharmacological Sciences. Basel: Birkhauser, 1994, p. 203-208; M. Shochina, W. Haddad, U. Meiri, and M. Horo-witz. J. Therm. Biol. 21: 289-295, 1996). We tested the hypothesis that heat acclimation alters splanchnic resistance artery sensitivity to norepinephrine (NE). Male Sprague-Dawley rats (n = 5) were acclimated to 35°C ambient temperature for 5-8 wk. Control rats (n = 5) were maintained at 22-23°C ambient temperature for 5-7 wk. Small mesenteric artery segments (2- to 3-mm length, 100- to 340-µm ID) were isolated, cannulated at both ends, and pressurized to 50 mmHg. Artery luminal diameter was measured in response to cumulative doses of NE (10⁹ to 10⁵ M) by using video microscopy. NE dose response was measured at 37 and 43°C bath temperatures. There were no differences in constriction responses to NE between acclimated and control rat arteries at either 37 or 43°C. We conclude that acclimation does not alter rat mesenteric artery sensitivity to NE.

isolated vessels; acclimation; rat