Direct sympathetic stimulation of the peripheral circula- tion via the activation of α 1 -adrenergic receptors on arterioles induces vasoconstriction and causes a compensatory increase in systemic vascular resistance and blood pressure. The arte- rial vasoconstriction is not uniform; marked redistribution of blood flow results. Selective perfusion to tissues occurs due to regional variations in arteriolar resistance, with blood shunted away from less essential organ beds such as the intestine, kid- ney, and skin. In contrast, the brain and heart have autoregu- latory mechanisms that attempt to preserve their blood flow despite a global decrease in cardiac output. Direct sympathetic stimulation also induces constriction of venous vessels, decreas- ing the capacitance of the circulatory system and accelerating blood return to the central circulation.