PREGNANCY-INDUCED PULMONARY-HYPERTENSION IN COWS SUSCEPTIBLE TO HIGH MOUNTAIN DISEASE

Observations in several species suggest that pulmonary vascular reactivity may be reduced during pregnancy. This hypothesis was tested in 2 groups of unanesthetized cows, one susceptible and one resistant to high mountain or brisket disease. At the altitude of residence (1524 m), mean pulmonary arterial pressure was elevated during pregnancy by 18% and total pulmonary vascular resistance by 32% in susceptible but not in resistant cows. During acute exposure to simulated altitudes of 2120-4550 m, pulmonary arterial pressure was increased by 16% and total pulmonary resistance by 28% during pregnancy in susceptible cows. The pulmonary pressor response to a 5 .mu.g/kg bolus of prostaglandin F2.alpha. was not different during pregnancy in either group. Resistant cows hyperventilated while pregnant, raising arterial partial pressure of O2 (PaO2) by 6 torr both at 1524 m and, on the average, by 7 torr at altitudes of 2120-4550 m. Susceptible cows increased their PaO2 less than did the resistant cows during pregnancy. Pregnancy was apparently associated with a greater rise in pulmonary arterial pressure and total pulmonary vascular resistance during acute hypoxia and failed to elicit as great a ventilatory response in susceptible than in resistant cows.