Neural control of gastric mucosal blood flow in the rat

This study was designed to determine (1) whether sympathetic nerve stimulation reduces gastric mucosal blood flow through the opening of submucosal arteriovenous anastomoses ("shunts"); and (2) whether parasympathetic nerve stimulation increases gastric mucosal blood flow through a direct effect on vascular smooth muscle as well as through metabolic factors secondary to increased acid secretion. An in vivo microscopy technique for the direct visualization of the rat gastric microcirculation was employed. Stimulation of the splanchnic nerve for 3 min caused an initial constriction of submucosal arterioles followed by escape (dilation during continued splanchnic stimulation) in all rats. No arteriovenous anastomoses were seen either in the resting state or during nerve stimulation. Mucosal studies with splanchnic stimulation revealed an initial progressive slowing of flow in the capillaries, followed by escape (partial return of flow). There were no significant differences between the times to maximum initial circulatory change in the submucosa and mucosa, and between the times to maximum escape in the submucosa and mucosa. These findings indicate that, in the rat, sympathetic stimulation decreases mucosal blood flow through a constricting effect on the supplying submucosal arterioles and not through the opening of "shunts". In studies with vagal stimulation, the submucosal arterioles dilated within 10 sec of beginning stimulation in 45 of 51 observations (P less than 0.001) and decreased in diameter within 10 sec of cessation of stimulation in 45 of 51 observations (P less than 0.001). The immediate dilation with stimulation and constriction with cessation of stimulation suggests a direct vasodilator effect of vagal stimulation on the gastric submucosal arterioles.