Differential Effects of Phentolamine and Bretylium on Pulmonary Vascular Responses to Norepinephrine and Nerve Stimulation 1

Summary The effects of specific adrenergic blocking agents on pulmonary vascular responses to sympathetic nerve stimulation and norepinephrine were evaluated in the perfused dog lung using a new right heart catheterization procedure which avoids dissection and cannulation of lobar vessels. The increase in pulmonary vascular resistance in response to nerve stimulation and norepinephrine but not serotonin was antagonized by phentolamine, an alpha receptor blocking agent. Responses to nerve stimulation but not exogenous norepinephrine were antagonized by bretylium, an adrenergic nerve terminal blocking agent. It is concluded that the pressor response to nerve stimulation is due to activation of alpha receptors by endogenous norepinephrine released from sympathetic nerve endings in the pulmonary blood vessels.