Effects of alpha 1-adrenoceptor and Ca2+ channel inhibition on norepinephrine-induced thermoregulatory behavior in the cold.

This experiment examined whether paradoxical temperature-dependent effects of norepinephrine (NE) can be blocked by the alpha 1-adrenoceptor antagonist WB 4101 (WB) and the Ca(2+)-channel blocker nifedipine. An operant lever-pressing task was used to measure the demand for heat in a cold environment. As noted previously, NE alone (250 micrograms/kg) produced a substantial and significant increase in the demand for heat, and yet post-test colonic temperature (Tc) fell. When tested alone, WB and nifedipine also increased the demand for heat, but this was sufficient to maintain Tc. When combined with NE, WB and nifedipine reduced the demand for heat and the fall in Tc such that there were no differences between the effects of the blockers given alone or with NE. These results indicate that paradoxical thermoregulatory effects of NE in the cold can be antagonized effectively by either an alpha 1-adrenoceptor antagonist or a Ca(2+)-channel blocker.