THE EFFECT OF INHALATION OF PLATELET-ACTIVATING-FACTOR ON THE PULMONARY CLEARANCE OF TC-99M-DTPA AEROSOL

Platelet-activating factor (PAF) is a short-acting, lipid-soluble auto coid, inhalation of which causes an immediate pulmonary vascular seque stration of granulocytes and a peripheral neutropenia. We investigated the effect of PAF inhalation on the pulmonary clearance rate of inhal ed Tc-99m-DTPA in order to test the hypothesis that the pulmonary sequ estration of granulocytes results in acute lung injury. In nine normal nonsmoking adults, the rate of clearance of DTPA, corrected for backg round activity, was 1.5 (SD 0.7) %/min over the first 10 min after inh alation. Inhalation of 4.8 mu g PAF abruptly increased the clearance r ate to a mean value of 2.3 (1.4) %/min (p < 0.05). No increase in clea rance was observed in four nonsmoking subjects who inhaled vehicle onl y. The mean overall increase after PAF was 87% of the baseline clearan ce, significantly different (p < 0.05) from the corresponding change i n the control group, which was -17%. After PAF, the clearance rate ret urned to baseline values within 10 min in all subjects. In all subject s who inhaled PAF, but in none who inhaled vehicle, there was an immed iate neutropenia of 51 (SD 25) % of the baseline value (p < 0.01). Thi s neutropenia persisted longer than the corresponding accelerated DTPA clearance and was still 74 (36) % of the baseline value at 10 min. Fu rthermore, there was no correlation between the increase in DTPA clear ance induced by PAF inhalation and the decrease in peripheral blood gr anulocyte count. We conclude that PAF inhalation results in an increas e in pulmonary DTPA clearance, probably not mediated by pulmonary vasc ular granulocyte sequestration.