The effect of age on pulmonary epithelial permeability in unanesthetized lambs.
Pulmonary epithelial permeability was measured 1) in unanesthetized sheep, and 2) longitudinally in growing lambs. Awake sheep were intubated and a solution of 51Cr-ethylenediaminetetraacetic acid and 125I-antipyrine was instilled in the intrathoracic trachea via the nasotracheal tube. Arterial blood was drawn 1-25 minutes after the instillation. The ratios of the counts of 51Cr to 125I at 7, 10, and 13 min were calculated and averaged for each animal. Data from six adult sheep showed that the mean +/- SE of the permeability ratio was 0.012 +/- 0.003 and was reproducible over three months. When measured twice within two hours, the second ratio was significantly higher than the first (0.021 +/- 0.004 vs. 0.011 +/- 0.003, n = 6, P less than 0.05). One hour of general anesthesia with methoxyflurane did not alter the permeability ratio significantly. Ten lambs were studied longitudinally 10 hours and 5, 10, 20, and 30 days after delivery. Within the first 24 hours of life the permeability ratio was 0.035 +/- 0.007, significantly greater (P less than 0.05) than the adult value. At five days there was no significant difference between lambs and adult sheep. Throughout the first month of life, the permeability ratio in lambs remained at at the adult level. In summary, 1) pulmonary epithelial permeability can be assessed in awake lambs and adult sheep, 2) the permeability ratio is reproducible for three months but should not be measured within two hours, 3) newborn lambs have a significantly higher ratio than older lambs or adult sheep, and 4) the ratio reaches the adult level within five days after birth.