The effect of intracerebroventricular administration of catecholamines and their antagonists on rectal temperature of Mastomys natalensis

Summary

Noradrenaline (NA), adrenaline (ADR), isoprenaline (ISO) and dopamine (DA) were given through a chronically implanted cannula in the lateral cerebral ventricle of Mastomys natalensis. Low doses of NA (0.05–0.25 μg) reduced rectal temperature while larger doses (0.35 μg upwards) produced dose-dependent hyperthermia. The hypothermic effect was antagonised by α-adrenceptor and the hyperthermia by β-adrenoceptor antagonists. α-Methyl noradrenaline produced less hyperthermia but it antagonised the hyperthermic effect of NA. Adrenaline (0.1–10 μg) was ineffective per se but when given after tolazoline it produced hyperthermia and after propranolol it produced hypothermia. The dose-dependent hyperthermia with isoprenaline (0.1–10 μg) was blocked by propranolol and MJ-1999. Dopamine (0.5–20 μg) and its agonists apomorphine, amantadine and BS 9641 produced hyperthermia which was antagonised by haloperidol and pimozide but not by α- or β-adrenoceptor antagonists. Noradrenaline (1.0 μg) produced hypothermia at ambient temperature of 10°C and 16°C. It had no effect at 20°C which seems to be the thermoneutral zone for mastomys. The hyperthermic effect at 33°C was less than at 24°C. Dopamine (10 μg) response was attenuated at 33°C and unaffected at other ambient temperatures. It is concluded that α- and β-adrenoceptors and DA-receptors exist in the central thermoregulatory mechanism in mastomys. The α-receptors are concerned with lowering the body temperature whereas the β-receptors and DA-receptors are involved in raising it.