EFFECT OF ACTIVATION ON NEUTROPHIL-INDUCED HEPATIC MICROVASCULAR INJURY IN ISOLATED RAT-LIVER

Polymorphonuclear neutrophils (PMNs) have been implicated in microvasc ular injury following ischemia and reperfusion (I/R) but the relative contribution of obstruction versus toxic mediators is not well defined . Therefore, the present study was performed to determine the contribu tion of exogenous or endogenous activation on PMN-induced microvascula r and hepatocyte injury. Rat livers were isolated and perfused at cons tant pressure with Krebs buffer with red cells (Hct-10%) and monitored for perfused sinusoids (PS) and dead hepatocytes (propidium iodide-st ained, DH) by intravital microscopy. PMNs isolated from the peritoneum after oyster glycogen injection were added to the perfusate either wi thout or with activation by phorbol myristate acetate (PMA, 160 nM). U nactivated PMNs stuck in the liver but had no significant effect on ei ther perfused sinusoids (11.1 +/- .4/field, unactivated PMNs versus 11 .9 +/- .5/field, the time-matched control) or dead hepatocytes (1.2 +/ - .4/field, unactivated PMNs versus 1 +/- .3/field, the time-matched c ontrol). Infusion of PMA-activated PMNs resulted in significant decrea se in perfused sinusoids and increase in DH (9.5 +/- .3/field for PS a nd 3.2 +/- .6/field for DH, respectively). In contrast, when PMNs were ''activated'' by infusion into a liver previously made ischemic for 3 0 min, DH were significantly increased after 60 min (26.2 +/- 4.5/fiel d, I/R plus PMNs versus 12.4 +/- 2/field, I/R only) but perfused sinus oids were not different from ischemia alone. These results demonstrate that oxidatively quiescent PMNs do not cause cellular or microvascula r injury in spite of microvascular accumulation. Activated PMNs damage microcirculation or hepatocytes depending on the nature of the activa tion.