Secondary fall in blood pressure following noradrenaline infusion in the cat.

Abstract

Summary.The rise in blood pressure caused by an infusion of noradrenaline in the cat is frequently followed by a marked fall in blood pressure to subnormal levels, often lasting for 20–40 minutes.The sensitivity to single injections of noradrenaline is diminished during the first part of this period. After section of the buffer nerves the fall after noradrenaline infusion is prolonged and often enhanced.Intravenous infusions of calcium chloride reduce the blood pressure fall after noradrenaline.Only a brief and moderate fall is seen in animals having received TEAB in transmission blocking doses. This fall can be abolished by small doses of ergotamine.It is concluded that the fall in blood pressure after noradrenaline is partly due to a blocking effect on transmission within the vasomotor system.Certain implications of the present observations for the therapeutic use of noradrenaline infusions in man are briefly discussed.