Calcium increases in pulmonary alveolar fluid in lambs at birth

Calcium concentration in fetal lung fluid in lambs is relatively low, about 1.0 mEq/liter, and its concentration in alveolar fluid in mature rabbits is about 3 mEq/liter. To see if the Ca++ concentration changes at birth, we measured alveolar Ca++ as soon as possible after delivery by cesarean section and the onset of ventilation in eight anesthetized lambs at 144 days gestation. Subpleural alveoli were punctured with Ca++ selective microelectrodes as soon as 4 min and as late as 220 min after the onset of mechanical ventilation. The [Ca++] was 1.2 +/- 0.2 mEq/liter (mean +/- SD, n = 8) in fetal lung fluid collected before ventilation. After about 25 min of ventilation, alveolar Ca++ was not different from that in term lambs 24 to 72 h old (3.3 +/- 0.6 mEq/liter, n = 8). The [Ca++] increased with a t1/2 of about 10 min. Thus, alveolar Ca++ assumes a mature character very rapidly after the start of breathing in term lambs.