Hypotension produced by intravenous apomorphine in the anaesthetized dog is not centrally mediated

1 Intravenous administration of apomorphine (1.25 to 20 microgram/kg) in the anaesthetized dog produced a dose-dependent decrease in blood pressure which was antagonized by haloperidol but not influenced by propranolol or atropine. 2 Intracarotid administration of apomorphine produced a systemic hypotension which was significantly smaller than that seen with intravenous injection. 3 Doses of apomorphine that caused a decrease in blood pressure on intravenous injection, had no effect on blood pressure or caused retching accompanied by an increase in blood pressure on intravertebral or intracisternal administration. The animals showed a marked hypotension on intravertebral or intracisternal injection of clonidine. 4 From these results it is concluded that the hypotension seen with intravenous apomorphine cannot be explained by a central site of action.