Effect of intravenous platelet-activating factor on bovine pulmonary mast cells

The effect of platelet-activating factor (PAF) on bovine pulmonary mast cel ls (MCs) was investigated in calves aged 1-4 months. PAF was administered o ver a 5-min period at a rate of 50 ng/kg/min to six animals, which were kil led approximately 10 min later. No macroscopical lesions were observed in t he lung tissue of five control calves. On semi-thin toluidine-blue stained sections, MG cytoplasm showed profuse deep-blue granulation. In the lung ti ssues of PAF-treated calves, striking interstitial, alveolar and interlobul ar oedema and emphysema were observed. MC granules occurred at the peripher y of the cytoplasm and MC nuclei were easily detectable. Moreover, the numb er of granules in the MC cytoplasm was remarkably low. A few granules with some metachromatic material were sometimes detected outside the cell limits . Ultrastructurally, the matrix pattern of the MC granules in lung tissues of control calves was either amorphous or granular. In lung tissues of the PAF-treated calves, the granular matrix pattern was pronounced, varying fro m fine- to coarse-grained, and the MCs were of reduced size, with many fili form processes and exocytotic vesicles. These findings indicate that pulmon ary MG degranulation was induced by PAF in healthy calves. (C) 2001 Harcour t Publishers Ltd.