Methylprednisolone prevents venous resistance increase in oleic acid lung injury

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Abstract
In the isolated perfused dog lung lobe, the effect of oleic acid (OA) and edema on the distribution of pulmonary vascular resistance (PVR) and whether methylprednisolone pretreatment affected the partitioning of PVR or rate of edema formation associated with OA injury were determined. Lobe weight was continuously monitored with pulmonary vascular resistance (zone III) partitioned into upstream and downstream components and pulmonary capillary pressure (Pc) estimated by the venous occlusion technique. At constant perfusion pressure, control lobes (group 1; n = 7) were given 1 .mu.l/kg body wt OA and a 2nd group (group II; n = 7) was pretreated with 5.1 mg/g lobe wt methylprednisolone 1 h before OA. In a 3rd group of lobes (group III; n = 6) given neither OA nor methylprednisolone, venous pressure was elevated to produce a hydrostatic edema. After OA, both groups I and II showed similar reductions in effective lobe compliance and serum Ca2+ and increases in plasma protein. Venous O2 partial pressure (PO2) fell more rapidly in group I than in group II lobes. A linear rate of weight gain was observed in all lobes. Total weight gain 3 h after OA in group I (36 .+-. 5%) was greater than in group II lobes (24 .+-. 4%). Group III averaged a 41 .+-. 3% weight gain after venous pressure elevation. In group I the ratio of downstream to total PVR (.gamma.) increased from 0.43 to 0.04 to 0.58 .+-. 0.05 and Pc rose from 5.5 .+-. 0.2 to 7.5 .+-. 0.8 Torr after OA. In lobes pretreated with methylprednisolone (group II) neither .gamma. nor Pc changed after OA. Edema formation alone (group III) did not alter .gamma. or Pc. The increase in .gamma. and Pc in group I was correlated with a decline in venous blood PO2. OA appears to produce edema both by increasing capillary membrane permeability and by elevating Pc via an increase in downstream (venous) resistance. Methylprednisolone pretreatment may attenuate edema formation by preventing an elevation in .gamma. or Pc with OA injury.