Pharmacology of the hemodynamic and myocardial response to occlusion of the mesenteric artery in the cat.

Occlusion of the superior mesenteric artery in the cat produces increases in heart rate, systemic pressure, cardiac output and muscle blood flow. Total peripheral resistance is reduced and regional resistance in skin increased. Blockade of the right and left cardiac nerves with xylocaine lowered basal heart rate and reduced cardiac output. The increase in heart rate produced by occlusion of the artery (MAO) was prevented by blockade of the stellate ganglia and cardiac nerves. Propranolol lowered basal heart rate and cardiac output and subsequently blocked the increase in both parameters during MAO. The increase in muscle blood flow was also blocked resulting in an increase in total resistance. We conclude that, in the cat, MAO reflexly increases myocardial tone and enhances venous return from muscle, the latter by a reflex beta adrenergic vasodilation. Both factors provide for the increase in cardiac output. A reflex beta adrenergic vasodilation in muscle, evoked by vasoconstriction in the mesenteric bed, may contribute to survival in the hemorrhaged animals, since capillary exchange in muscle may be increased by this reflex and fluid shifted from the extra--to the intravascular compartment.