RESPIRATORY STIMULATION BY ANGIOTENSIN-II

The changes in breathing accompanying increases in arterial pressure caused by i.v. injections of angiotensin II were examined in dogs anesthetized with chloralose andin unanesthetized rabbits. They were compared with the effects on breathing caused when the .alpha.-adrenergic vasoconstrictor, phenylephrine or inflation of an aortic balloon were used to raise blood pressure to comparable levels. Phenylephrine and balloone inflation always depressed breathing. This depression was secondary to the increase in arterial pressure and was abolisehd by denervation of the arterial baroreceptors. In every animal, ventilation was greater with angiotensin II than it was at a comparable blood pressure achieved with phenylephrine or balloon inflation. When compared with control levels of ventilation angiotensin II sometimes had little effect. When carotid sinus and vagus nerves were cut, angiotensin II consistently stimulated breathing. Angiotensin II had an independent stimulating effect on ventilation which cannot be attributed to inhibition of any baroreceptor-mediated respiratory restraint, nor to stimulation of either arterial chemoreceptors or intrathoracic receptors running to the CNS through the vagus.