The Cardiovascular Effects of Substance P in the Chicken

Abstract

In 1931, Euler and Gaddum reported the presence of an unidentified depressor substance in extracts of various tissues, particularly those of the brain and intestine. This depressor agent was referred to as "substance P" and it was suggested that the fall in arterial pressure produced by substance P in the atropinized rabbit is due to peripheral vasodilation. Subsequent investigations have shown that intraarterial injections of substance P cause a pronounced dilatation of the vessels in the perfused, chronically-devervated rabbit ear. The depressor activity of substance P has also been demonstrated in other mammals and its hypotensive effect has been found to be unaffected by atropine, antihistaminics or ganglionic-blocking agents. In cats and rabbits, intracisternal or intraventricular injections of substance P have been observed to produce prominent respiratory manifestations with very slight and variable hemodynamic effects. In healthy human subjects, it has been reported that intravenous infusions of substance P produce facial flushing, increase blood flow in the muscles and skin, hypotension and tachycardia. These carious observations indicate that in mammals, the predominant factor responsible for the depressor response to substance P is a peripheral vaodilatation. The present experiments were conducted to investigate the cardiovascular effects of substance P in the chicken.