Effects of hydralazines on canine muscarinic ganglion transmission.

The effects of hydralazine, dihydralazine and 4-propyl-1-hydrazinophthalazine (4-propylhydralazine) were investigated on reflex pressor responses to increased intracranial fluid pressure (IIP) during occlusion of the abdominal aorta and the vena cava (MVO). It has been shown that application of MVO, caudal to the renal arteries, produces two independent vascular zones in the animal (Steinberg and Hilton, 1966a). Increasing intracranial fluid pressure during MVO elicits a reflex pressor response which consists of two components. One component is blocked by the nicotinic ganglionic blocking agent, chlorisondamine, and the other component is blocked by small doses of atropine. It was found that hydralazine and dihydralazine were effective in blocking residual pressor responses following partial blockade of reflex pressor responses to IIP with chlorisondamine. 4-Propylhydralazine, which is chemically similar to hydralazine and dihydralazine, was less active in inhibiting the residual pressor responses. It is suggested that hydralazine may act in part by interfering with muscarinic ganglionic transmission.