Effects of indomethacin on PMA-induced pulmonary endothelial enzyme dysfunction in vivo

Abstract

We investigated the effects of phorbol myristate acetate (PMA) on metabolic pulmonary endothelial ectoenzyme dysfunction. Anesthetized rabbits were placed on total heart bypass, and the single-pass transpulmonary metabolism of [3H]benzoyl-Phe-Ala-Pro (BPAP) by endothelial-bound angiotensin-converting enzyme (ACE) and [14C]adenosine 5'-monophosphate (AMP) by 5'-nucleotidase (NCT) was calculated before and after PMA (10 micrograms/kg iv), a dose that does not produce histologically evident endothelial damage. Under conditions of partial microvascular recruitment (blood flow = 400 ml/min through the entire lung), PMA, but not the vehicle, significantly reduced substrate utilization of both BPAP and adenosine 5'-monophosphate (AMP) and increased the apparent Michaelis constant (Km) values of ACE for BPAP, indicative of metabolic dysfunction. These changes were completely prevented by pretreatment with indomethacin. Under conditions of near full microvascular recruitment (blood flow = 640 ml/min through the left lung only), PMA similarly reduced substrate utilization and increased the apparent Km of ACE for BPAP. In this case, however, indomethacin failed to prevent the observed PMA-induced metabolic dysfunction. We conclude that PMA alters endothelial ectoenzyme substrate metabolism independently from changes in pulmonary blood flow; indomethacin appears to antagonize the effects of PMA under conditions of partial microvascular recruitment only, perhaps by diverting flow to previously unperfused, unexposed to PMA, and hence metabolically healthy vessels.

Pulmonary endothelium in acute lung injury: from basic science to the critically ill

“…Pretreatment of rabbits with indomethacin, under partial lung microvascular recruitment, protects against PMAinduced pulmonary endothelial enzyme dysfunction, probably by diverting flow to previously unperfused (i.e., unexposed to PMA) capillaries. Under nearly full microvascular recruitment, the above protective effect of indomethacin is abolished [69]. In a similar respect selective inhibition of the inducible COX isoform protects against the endotoxin-related loss of perfusion redistribution in an oleic acid induced dog ALI model, an effect mediated by PGI 2 [70].…”

“…PCEB-ACE activity reduction is among the earliest signs in various ALI animal models, preceding changes in parameters such as acid-base balance, gas exchange, hemodynamic parameters, increased permeability, and morphological changes at the light and electron-microscopic level. This is the case following administration of bleomycin to rabbits [79], exposure of rabbits to hyperoxia [80], PMA administration to rabbits and dogs [69,81], and chest irradiation to rabbits [82,83]. Similarly, pulmonary endothelial ACE activity depression, determined by the decreased pulmonary uptake of an anti-ACE monoclonal antibody, occurs in rats secondary to normoxic lung ischemia/reperfusion [84].…”

Reduced lung endothelial angiotensin-converting enzyme activity in Watanabe hyperlipidemic rabbits in vivo

“…3). This finding appears to differentiate the PCEB ACE activity reduction in WHHL rabbits from models of acute lung injury, such as phorbol 12-myristate 13-acetate induced (11), where increases in K m , i.e., decreases in ACE affinity for BPAP, occurred. This probably suggests that noxious stimuli that induce acute pulmonary endothelial dysfunction might exert their action by altering either the enzyme molecule or the plasma membrane properties, whereas chronic hyperlipidemia might induce a decrease of otherwise functional PCEB ACE.…”

“…In this study, we estimated PCEB ACE and NCT activities in vivo by means of indicator-dilution techniques in WHHL and NZ control rabbits. We chose to study the activities of the aforementioned ectoenzymes because numerous studies (11,29,31,32,37) performed in animals, and more recently in humans, have shown that ectoenzyme dysfunction is an early and sensitive marker of lung vascular injury. In addition, differences in PCEB ectoenzyme activity, if present, might have significant biological implications on the pulmonary and systemic vascular homeostasis in this animal model of chronic hypercholesterolemia.…”

“…The use of these techniques in various animal models has provided evidence that pulmonary capillary endothelium-bound (PCEB) ectoenzyme, especially ACE, dysfunction is an early and sensitive marker of various types of acute pulmonary endothelial injury (11,29,32,37). In this study, we tested the hypothesis that PCEB ectoenzyme activity, an index of pulmonary endothelial function, is altered when exposed to long-term hyperlipidemia.…”