NBT reactivity correlates to the distribution of PMNs between rat pulmonary and systemic circulation

The rat systemic and pulmonary vascular transit times of radiolabeled polymorphonuclear granulocytes (experimental population referred to as "Polys") and mononuclear leukocytes (experimental population referred to as "Monos") (111In) in relation to those of erythrocytes (51Cr) were measured under physiological conditions. Results were also expressed as "circulating" pool and "marginated" pool of the two leukocyte fractions, and it was investigated whether the degree of spontaneous granulocyte activation, measured with the nitro blue tetrazolium (NBT) reduction test, was of importance for the retention of Polys in the lungs. The measured mean vascular transit was similar for Monos and Polys and several times slower than that of the erythrocytes in the pulmonary (17.4 times) and the systemic (4.1 times) vascular beds. The percentage of NBT-positive cells was < 10% in most animals, indicating a low level of spontaneous granulocyte activation. Increasing levels of NBT-positive cells correlated with a redistribution of granulocytes from the systemic marginated cell pool to the pulmonary marginated cell pool. Microscopic evaluation of sections from embedded lung tissue biopsies, obtained after intravital staining of the leukocytes, confirmed the isotope data on pulmonary transit.