Effects of hydralazine on canine muscarinic ganglion stimulation

The effects of hydralazine upon the caudal pressor responses during occlusion of the abdominal aorta and vena cava evoked by: (1) preganglionic electrical stimulation of the lumbar sympathetic chain, (2) neostigmine and (3) McN-A-343 were investigated in the anesthetized dog. Hydralazine (10 microgram/kg, i.v.) produced a small but significant reduction of the pressor response to lumbar electrical stimulation prior and following blockade of nicotinic transmission with chlorisondamine (1.0 mg/kg). However, hydralazine was not effective in blocking the pressor responses elicited by neostigmine and McN-A-343. On the other hand, small doses of atropine (20 microgram/kg) produced a blockade of residual pressor responses evoked by all three stimuli. On the basis of these findings, the site of action of hydralazine appears to be different from that of atropine. It is proposed that hydralazine affects ganglionic transmission by acting at sites other than muscarinic in nature.