Adrenergic mechanisms in canine gastric circulation

The effects of adrenergic stimulation and blockade on the gastric circulation were studied in anesthetized dogs. Blood flow through the right and left gastric artery was measured electromagnetically. Norepinephrine and isoproterenol were injected intra arterially and intravenously before and after alpha and beta adrenergic blockade. Isoproterenol caused vasodilation of both right and left gastric circulations and this effect was attenuated by beta blockade. Epinephrine and norepinephrine induced constriction followed by dilation in both circulations. The constrictor components were attenuated or abolished by alpha adrenergic blockade and the dilator components were attenuated by beta adrenergic blockade. The right and left gastric vascular beds demonstrated quantitatively different responses to the same dose of each adrenergic amine. The left gastric circulation had a greater vasodilator response than did the right gastric circulation. These data support the classical concepts that epinephrine and norepinephrine are 'mixed' adrenergic agonists and isoproterenol is a 'pure' beta adrenergic agonist. The data further suggest that there is a differential in beta adrenergic receptor distribution with the left gastric vasculature demonstrating greater dilator responses than the right.