CONTRIBUTION OF LYMPHATIC MYOGENIC ACTIVITY AND RESPIRATORY MOVEMENTSTO PLEURAL LYMPH-FLOW

In II anesthetized spontaneously breathing rabbits, we studied the con tribution to total pleural lymph flow of myogenic activity of pleural lymphatics (''intrinsic mechanism'') and the effect due to mechanical action of respiratory movements (''extrinsic mechanism''). Isoncotic s aline solution (5 ml) containing 100 mu Ci of I-125-Iactate dehydrogen ase (LDH) was injected into right pleural space; in all but three cont rol rabbits, injectate contained 1 mM amiloride in dimethyl sulfoxide to induce relaxation of smooth muscle tone. At 3 h, rabbits were kille d and pleural fluid was collected and its volume measured. LDH radioac tivity in pleural liquid and parietal pleural tissue was counted. In c ontrol rabbits, net pleural liquid flow (J(net)) at 3 h was -0.17 +/- 0.04 (SD) ml.kg(-1).h(-1); LDH concentration (C) and quantity (and) de creased by 40.3 and 51.1% of initial value, respectively; total pleura l lymphatic flow (J(1)), calculated from LDH clearance, was 0.58 +/- 0 .01 ml.kg(-1).h(-1). In amiloride-treated rabbits, J(net) was 0.01 +/- 0.1 ml.kg(-1).h(-1), C decreased by 34.4% and and by 33.1%, and J(1) averaged 0.39 +/- 0.02 ml.kg(-1).h(-1). C in parietal pleura, rich in lymphatics, was 13-fold higher in control than in amiloride-treated an imals. The significant decrease of pleural lymphatic flow observed wit h amiloride (-40% relative to control) resulted from impairment of int rinsic mechanism, whereas, at comparable breathing frequencies, extrin sic mechanism remained unaltered. The direct effect of topical applica tion of 1 mM amiloride was confirmed on exposed mesenteric collecting lymphatic ducts (data from 5 rats): amiloride reduced lymph flow by 40 % by decreasing stroke volume without greatly affecting contraction ra te of lymphatic walls.