Numerous endogenous and exogenous humoral factors are capable of affecting the splanchnic circulation. Norepinephrine and high levels of epinephrine produce intense vasoconstriction through the stimulation of adrenergic receptors. Other pharmacologic compounds that decrease splanchnic blood flow include vasopressin, phenylephrine, and digoxin.14 Low-dose dopamine causes splanchnic vasodilation, whereas higher doses lead to vasoconstriction by stimulating α-adrenergic receptors. Papaverine, adenosine, dobutamine, fenoldopam mesylate, and sodium nitroprusside are exogenous agents that increase mesenteric blood flow. In addition, various naturally occurring agents can serve as splanchnic vasodilators, including acetylcholine, histamine, nitric oxide, leukotrienes, thromboxane analogues, glucagon, and an assortment of gastrointestinal hormones. The effects of prostaglandins are variable.