EFFECT OF INHALED NITRIC-OXIDE ON THE HYPOXIC PULMONARY VASOCONSTRICTOR RESPONSE IN ANESTHETIZED CALVES

The effect of inhaling nitric oxide in the hypoxic pulmonary vascular response was measured in five calves anaesthetised with a combination of guaiacol, ketamine and xylazine. Alveolar hypoxia was induced by me ans of the inhalation of a gas mixture with an inspiratory oxygen frac tion of 14-18 per cent. This alveolar hypoxia resulted in a pronounced pulmonary hypertension (mean pulmonary artery pressure in hypoxic ani mals : 30.2 mmHg). Inhalation of 20 and 40 ppm of nitric oxide signifi cantly attenuated the hypoxia induced pulmonary hypertension. The effe ct ceased once nitric oxide administration was stopped. A concentratio n of 40 ppm of nitric oxide fully abolished the hypoxia induced pulmon ary hypertension (mean pulmonary artery pressure during inhalation of 40 ppm nitric oxide : 22.8 mmHg). Inhalation of nitric oxide had no ef fect on systemic arterial blood pressure nor on systemic vascular resi stance. It was concluded that inhalation of 20 or 40 ppm of nitric oxi de prevented a selective pulmonary vasoconstriction during alveolar hy poxia in calves, which may be helpful in the treatment of acute respir atory disorders in calves.