Analysis of histamine receptors in the central thermoregulatory mechanism of Mastomys natalensis.

1 The effect of intracerebroventricular (i.c.v.) injection of histamine on the rectal temperature of Mastomys natalensis at ambient temperatures of 10, 24 and 33 degrees C has been studied. 2 Low doses (0.1-1.0 microgram) of histamine produced hypothermia while larger doses (5-20 micrograms) produced dose-dependent hyperthermia. The hypothermic effect was significantly antagonized by mepyramine while the hyperthermia was blocked by cimetidine. 3 Histamine H1-receptor agonists, 2-methyl-histamine and 2-pyridyl-ethylamine, also produced hypothermia which could be blocked by mepyramine. 4 Histamine H2-receptor agonists, impromidine and dimaprit, produced hyperthermia which was antagonized by cimetidine. 5 Pretreatment of the animals with a beta-adrenoceptor antagonist, MJ1999, did not affect the response to histamine. 6 The hyperthermic effect of histamine (10 micrograms) was most marked at 10 degrees C and was attenuated at 33 degrees C. 7 It is concluded that both H1 and H2-histamine receptors are present in the brain of Mastomys. The H1-receptors mediate hypothermia and H2-receptors hyperthermia.