Vasodepression induced by acetylcholine in the atropinized dog.

The pressor response to acetylcholine in the atropinized dog resulted from an increase in cardiac output. The pressor response was attributed solely to the release of adrenaline from the adrenal medulla. After giving compound P-286 (N-diethylaminoethyl-N-isopentyl-N'N'-di-isopropylurea) to these dogs, acetylcholine lowered blood pressure, owing to a decrease in total peripheral resistance in the absence of an increase in cardiac output. P-286 presumably blocked the liberation of adrenaline from the adrenal glands by acetylcholine. The blood vessels contributing to the fall in peripheral resistance were not in the intestines. The fall in blood pressure was not blocked by dichloroisoprenaline and it was still present in dogs treated with reserpine. It is suggested that the fall in blood pressure was due to stimulation of ganglion cells subserving vasodilatation.