Mode of action of intravenous nicotine in causing a fall of blood pressure in the cat

Abstract

Small amounts of nicotine (5–20 μg/kg) injected into the femoral vein or pulmonary artery of cats anaesthetized with chloralose usually caused a fall in blood pressure within a few seconds of their injection. The fall in blood pressure was usually followed by a much larger rise. When similar amounts of nicotine were injected into the left atrium there was no initial fall in blood pressure and this was also the usual result when nicotine was introduced into the lungs in tobacco smoke. Analysis of this nicotine depressor response has shown that it is due to stimulation of sensory nerve endings in the lungs, the afferent nerve of the reflex response being the vagus. Two efferent pathways are involved — the vagus and the sympathetic nerves to the blood vessels.