Effects of a thromboxane A2 analogue and prostacyclin on lung fluid balance in newborn lambs.

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Abstract
We have previously shown that the pulmonary venoconstriction produced by a stable thromboxane A2 analogue (STA2) is attenuated by prostacyclin (PGI2), but PGI2 increases the STA2-induced edema. The present study was designed to determine the effects of STA2 and PGI2 on the fluid balance in isolated blood-perfused newborn lamb lungs. Vascular permeability was evaluated by use of the fluid filtration coefficient (Kf) and the osmotic reflection coefficient for total proteins (sigma, hematocrit-protein double indicator technique), and pulmonary capillary pressure (Pc) was estimated by the double occlusion technique. All lungs had a period of hydrostatic stress induced by elevation of the left atrial pressure from 5 to 20 mm Hg to promote fluid filtration, and the rate of lung weight gain (delta W/delta T) during this period was determined. Studies were made in four groups; before the hydrostatic stress, lungs were given 1) STA2 (50 micrograms, n = 6), 2) PGI2 (0.4 micrograms/kg/min, n = 6), 3) both PGI2 and STA2 (n = 6), or 4) vehicles (control, n = 5). Measurements of Kf were made at the baseline period and after the hydrostatic stress. Kf was significantly increased by 76% with STA2, by 121% with PGI2, and by 157% with both PGI2 and STA2, but remained constant in controls. In comparison with control lungs, a similar delta W/delta T was observed with less of an increase in Pc during the hydrostatic stress in the STA2 group, and greater values of delta W/delta T were obtained with smaller elevations in Pc in the groups receiving PGI2 or both PGI2 and STA2.(ABSTRACT TRUNCATED AT 250 WORDS)