PMA-activated neutrophils decrease pulmonary endothelial ectoenzyme activities in perfused rabbit lungs.

We have studied the effects of phorbol 12-myristate 13-acetate (PMA, 15 micrograms) on pulmonary endothelial ectoenzyme [angiotensin-converting enzyme (ACE) and 5'-nucleotidase (NCT)] function in isolated rabbit lungs perfused in situ with platelet-poor (PPP) or platelet-rich (PRP) plasma in the presence or absence of neutrophils. Enzyme activities were estimated from the hydrolysis of the substrates [3H]benzoyl-Phe-Ala-Pro ([3H]BPAP) by ACE and 14C-labeled AMP by NCT during a single transpulmonary passage, using indicator-dilution techniques. In all treatment groups PMA produced a delayed increase in pulmonary vascular resistance to about three times the control value. PMA alone [in lungs perfused with PPP (n = 5 animals) or PRP (n = 6)] or neutrophils alone (in PPP-perfused lungs, n = 5) had no effect on enzyme activity. However, PMA-activated neutrophils (n = 5) decreased percent metabolism (%M) of [3H]BPAP from 87 +/- 3 to 77 +/- 4% (30 min after PMA), and the apparent first-order parameter [ratio of maximum activity to Michaelis constant (Amax/Km)] for ACE from 821 +/- 114 to 613 +/- 61 ml/min (30 min after PMA). At the same time, Km values of BPAP for ACE and AMP for NCT were elevated from 9.2 +/- 2.2 to 19.3 +/- 3 microM and 6.7 +/- 1.2 to 15.1 +/- 3.6 microM, respectively, whereas Amax (product of enzyme mass and rate of product formation, thus an index of perfused microvascular surface area) did not change.(ABSTRACT TRUNCATED AT 250 WORDS)