ANALYSIS OF HISTAMINE RECEPTORS IN THE CENTRAL THERMOREGULATORY MECHANISM OF Mastomys natalensis

Abstract

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°C has been studied. 2 Low doses (0.1–1.0 μg) of histamine produced hypothermia while larger doses (5–20 μg) 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 β-adrenoceptor antagonist, MJ1999, did not affect the response to histamine. 6 The hyperthermic effect of histamine (10 μg) was most marked at 10°C and was attenuated at 33°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.