Effects of dopaminergic antagonist and agonist on thermoregulation in rabbits

1. The effects of dopaminergic antagonist haloperidol and agonist apomorphine on the thermoregulatory responses of unanaesthetized rabbits to different ambient temperatures (Ta) of 2, 22 and 32 degrees C were assessed. 2. I.V. administration of haloperidol produced dose-dependent hypothermia at 2 and 22 degrees C Ta. At 2 degrees C Ta the hypothermia was due to a decrease in metabolic heat production. At 22 degrees C Ta the hypothermia was brought about by a decrease in metabolism and an increase in ear blood flow. However at 32 degrees C Ta, there was an increase in rectal temperature in response to haloperidol application; this hyperthermia was due to a decrease in both the ear blood flow and respiratory evaporative heat loss (Eres). 3. I.V. administration of apomorphine produced dose-dependent hyperthermia at all the ambient temperatures studied. At 2 degrees C Ta the hyperthermia was due to an increase in metabolism. At both 22 and 32 degrees C, the hyperthermia was brought about by an increase in metabolic heat production and a decrease in ear blood flow. Also, there was an increase in Eres in response to apomorphine at 22 degrees C Ta. 4. The data, in general, indicate that dopamine agonist activates all effector pathways which modulate the autonomic processes of thermoregulation (i.e. respiratory heat loss, peripheral vasomotor tone and metabolism), and that the dopamine antagonist inhibits the activity in all three effector pathways. Such a clear pattern of results is readily expressible in terms of the 'Bligh' model dealing with the aminergic mechanisms of temperature regulation.