Analysis of hypothermic response to centrally administered histamine in pigeons

The effect of intracerebroventricular (i.c.v.) administration of histamine (H), H1- and H2-receptor agonists and their antagonists, on the cloacal temperature of pigeon has been investigated. Histamine produced a dose-dependent hypothermia at an ambient temperature of 24 degrees C which was significantly blocked by a combination of mepyramine and cimetidine but was only partially antagonized by either of them alone. H1-receptor as well as H2-receptor agonists also produced hypothermic response with a time-course similar to that of H. Their effects were also significantly antagonized by mepyramine and cimetidine respectively. The histamine response was not modified by pretreatment with alpha- or beta-adrenoceptor antagonists. Histamine produced an insignificant hyperthermia at 10 degrees C but the hypothermic effect increased as the ambient temperature was raised up to 40 degrees C. It is concluded that both H1- and H2-histamine receptors are present in the brain of pigeon and are responsible for H-induced hypothermia.