We explored the hemodynamic effects of rapid injection of 0.9% saline and arterial blood into the canine superior mesenteric artery in anesthetized animals. Mesenteric artery blood flow and pressure were measured in the vessel distal to the site of injection. Injection rates were at or below the rate of blood flow in the mesenteric artery. Rapid injection of saline caused increases in blood flow and decreases in pressure in the mesenteric artery, with responses to saline occurring during or shortly after the period of injection. Injection of arterialized blood into the artery prompted changes resembling those with saline. Injection of blood for up to 16 sec at a rate which was equal to the resting blood flow in the vessel increased both flow and pressure during the period of injection. Blood flow continued at an elevated level for many seconds after cessation of injection. During this time, pressure in the artery fell to a level below the control value. Calculated mesenteric vascular resistance exhibited a decrease during and following injection. Our findings suggest that the hemodynamic response of the superior mesenteric artery to a pulsation of blood or saline is vasodilation.

In an effort to evaluate the "spillover method" of measuring blood flow during angiography, we explored the effects of rapid injection of diatrizoate meglumine and diatrizoate sodium (Renografin-76) at rates no greater than resting blood flow in the superior mesenteric artery of anesthetized dogs. An increase in mesenteric blood flow and a decrease in mesenteric arterial pressure occurred many seconds after cessation of the injection. The dilation effected by the contrast agent was less marked at elevated blood flow values than at resting flows. The pattern of response to diatrizoate meglumine and diatrizoate sodium resembled that observed with vasodilator drugs. Our findings also suggest that the initial vascular response to a pulsation of the diatrizoate medium is vasodilation.