Abstract

Renal (cortex and medulla) and splanchnic (duodenum, liver, pancreas and spleen) blood flows were measured with 25-mu radioactive microspheres in anesthetized, open-chest dogs. The effects of nicotine (36 micrograms/kg/min i.v.) before and after selective alpha adrenergic blockade (phenoxybenzamine, 1 mg/kg i.v.) and before and after combined alpha and beta adrenergic blockade (phenoxybenzamine, 1 mg/kg i.v. and propranolol, 1 mg/kg i.v.) were evaluated. Before adrenergic blockade, nicotine increased arterial pressure (+82%) but had heterogeneous directional effects on regional blood flows: pancreas (-64%), duodenum (-33%), kidney cortex (-31%), kidney medulla (-17%), liver (+5%) and spleen (+71%). Vascular conductance was reduced in kidney cortex (-61%), kidney medulla (-57%), duodenum (-59%), liver (-46%) and pancreas (-79%) and was not altered in spleen. Selective alpha adrenergic blockade prevented the hypertensive response to nicotine, but heterogeneous changes in regional flows persisted: pancreas (-40%), spleen (-40%), kidney medulla (-35%), kidney cortex (-31%), liver (+50%) and duodenum (+74%). After combined alpha and beta adrenergic blockade, nicotine increased systemic arterial pressure (+75%) and decreased vascular conductance in all tissues. Results indicate: 1) a heterogeneous influence of nicotine in renal and splanchnic circulations associated with regional differences in activities of alpha and beta adrenergic receptors and 2) a potent nonadrenergic vasoconstrictor response in these circulations to nicotine after blockade of alpha and beta adrenergic receptors.