Escape from vasoconstriction in the gastric microcirculation.

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