Cromolyn sodium decreases the pulmonary vascular response to alveolar hypoxia in lambs.

We investigated the effect of cromolyn sodium, a mast cell stabilizing agent, on the pulmonary vascular response to alveolar hypoxia in six chronically instrumented lambs aged 9 to 11 days. Each lamb was instrumented on day 6 or 7 for measurements of systemic arterial, pulmonary arterial and left atrial pressures, and pulmonary blood flow. The animals were allowed to recover from surgery at least 3 days before they were studied. Each animal was studied twice, once with a cromolyn sodium infusion and once with a normal saline infusion (placebo). These paired experiments were separated by 24 h. Physiologic measurements were made during a 1-min predose control period, after an 8-min drug or placebo infusion, and after a 15-min period of alveolar hypoxia. Cromolyn sodium infusion alone did not affect baseline cardiovascular variables. Alveolar hypoxia following placebo infusion produced an increase in pulmonary arterial pressure and pulmonary vascular resistance; these responses were blocked in the animals given cromolyn sodium prior to induction of hypoxia. These results show that cromolyn sodium blocks the pulmonary vascular response to hypoxia and provide indirect evidence that mast cell degranulation, with subsequent release of vasoactive agents, mediates the pulmonary vascular response to hypoxia in newborn lambs.