The hypothermic effects of dl-tetrahydropalmatine in rats.

Systemic administration of dl-tetrahydropalmatine (THP; 10-50 mg x kg(-1) intraperitoneally) produced a proportional decrease in both colonic temperature and release of hypothalamic serotonin (5-hydroxytryptamine (5-HT)) in rats at room temperature. The hypothermia was brought about by cutaneous vasodilation and decreased metabolism. The THP- induced hypothermia was significantly attenuated in rats with brain 5-HT depletion produced by control injection of 5,7-dihydroxytryptamine or in rats with 5-HT2A receptor activation produced by 1-(2,5-dimethoxy-4-iodophenyl) -2-aminopropane, or in rats with 5-HT1A receptor antagonist produced by (-)-pindolol. The results suggest involvement of serotoninergic antagonism in the THP-induced hypothermia in rats