Abstract

The thermoregulatory influence of changes in ambient temperature and intrahypothalamic injections of norepinephrine and 5-hydroxytryptamine was investigated in normothermic golden hamsters together with the receptor specificity and dose dependence of the effects exerted by these biogenic amines. Exposure of partially restrained hamsters to a cold environment resulted in shivering, vasoconstriction, postural buddling and an increase in cardiac rate. Heat exposure produced vasodilation and postural extension as well as a reaction in shivering and heart rate. Extreme hyperthermia ensued at ambient temperatures above 38°C. At an ambient temperature of 20°C, 1 µl injections of 0.03, 0.06 and 0.09 µmol of norepinephrine elicited an immediate and dose-dependent hypothermic response. Similar administration of 0.06 µmol of 5-hydroxytryptamine had no influence on thermoregulation in this species. The response to norepinephrine was consistently accompanied by decreases in shivering and cardiac rate as well as peripheral vasodilation and was abolished by the prior central administration of phentolamine. Similar pretreatment with atropine and methysergide did not alter the effects of norepinephrine.