Role of central dopaminergic mechanisms in piribedil and clonidine induced hypothermia in the rat

The colonic temperature of rats maintained at different ambient temperatures (6, 20 and 30°C) was measured following intraperitoneal injection of piribedil and clonidine. Piribedil caused a dose-dependent fall in temperature, most prominent at 6°C, which was attenuated by pretreatment with pimozide but not with phenoxybenzamine or propranolol.Intraperitoneal clonidine also produced dose-dependent hypothermia but this was not related to ambient temperature, since hypothermia was as great at 20°C as at 6°C. The clonidine induced fall was abolished by phenoxybenzamine but not by pimozide pretreatment.Selective depletion of brain dopamine, achieved by intracisternal 6-hydroxydopamine following intraperitoneal desmethylimipramine, significantly enhanced the hypothermic effect of piribedil at 6°C. By contrast the effect of clonidine was unchanged.It is suggested that the hypothermia induced by piribedil is due to stimulation of central dopaminergic receptors, while the effect of clonidine is probably mediated via adrenergic mechanisms.