Escape from vasoconstriction in the gastric microcirculation

Abstract

Escape of splanchnic resistance vessels from vasoconstriction due to adrenergic stimulation has been attributed to increasing submucosal blood flow due to dilation of submucosal arteriovenous anastomoses (shunts). This postulate, as applied to the rat gastric microcirculation, was studied by in vivo microscopy. Using an image-splitting TV microscope recording system, response of gastric submucosal arterioles (13–33 µm) to 3 min of left splanchnic nerve stimulation, norepinephrine superfusion, and vasopressin superfusion was measured. All stimuli produced initial vasoconstriction. Escape occurred in all rats with nerve stimulation and norepinephrine, but in only one of five with vasopressin. No shunts were seen. The study demonstrates that the gastric submucosal arterioles exhibit an escape phenomenon, suggesting that "autoregulatory escape" in other splanchnic beds also may be due to relaxation of constricted vessels and not to opening of shunts.