Effect of Substance P on Various Vascular Beds in the Dog

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Abstract
Using the electromagnetic flowmeter technique, the blood flow in the aorta, carotid, hepatic, superior mesenteric, renal and femoral arteries and portal vein was recorded during continuous i.v. infusion of synthetic Substance P (SP) in 8 dogs. Systemic and portal blood pressures were recorded. A significant decrease in mean arterial blood pressure was recorded at infusion of SP in the femoral vein at a rate of 2.5 ng × min-1× kg b.w.-1 or higher. Portal venous blood pressure increased. A rapid increase in the carotid, hepatic, mesenteric and portal blood flow was obtained at infusion rates of 1.2 ng × min-1× kg b.w.-1 or higher. The femoral artery responded with a late, transient increase in flow, with a return to the base level while the infusion was still in progress. The renal artery blood flow decreased slightly at low infusion rates and increased at higher. At SP infusions in the portal vein the infusion rate had to be increased to 20 ng × min-1× kg b.w.-1 or higher before any general vascular reactions were recorded, indicating that the liver has a high capacity for inactivating SP.