Lung water and vascular permeability in sheep. Newborns compared with adults.

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Abstract
To compare vascular permeability and water content in the lungs of newborn lambs with those in adult sheep, extravascular water and permeability surface area products (PS) were measured for 14C-urea and 14C-sucrose in nine 3- to 5-day-old lambs and 13 yearling sheep. In normal, unanesthetized animals, a mixture of 51Cr-erythrocytes, 125I-albumin, 3H-water, and either 14C-sucrose or 14C-urea was injected as a bolus into the right atrium and sampled blood from the thoracic aorta, calculating extravascular water and PS for urea and sucrose from the time-concentration curves of the tracers. Extravascular lung water and dry bloodless lung weight postmortem were measured. Normalized to dry lung weight, extravascular lung water by both techniques was similar in newborns and adults (indicator dilution values = 3.2 .+-. 0.03 (SEM [standard error of the mean] ml/g for lambs and 3.2 .+-. 0.03 for sheep; postmortem values = 4.07 .+-. 0.26 g/g for lambs and 4.03 .+-. 0.17 for sheep). In newborn lambs, PS calculated by integral extraction was 0.28 .+-. 0.04 (SEM) g/g dry lung for 14C-urea and 0.18 .+-. 0.04 for 14C-sucrose. These values were not significantly different from those for adult sheep (14C-urea PS = 0.26 .+-. 0.05; 14C-sucrose PS = 0.08 .+-. 0.03). When normalized to dry lung weight, newborn and adult sheep have similar lung water and vascular permeability to small hydrophilic molecules and that indicator methods for measuring PS and lung water are feasible in newborns.

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