Activation of the contact phase of coagulation has been implicated in the pathogenesis of septic shock. We wanted to determine if inhibition of plasma kallikrein can prevent arterial hypotension and liberation of kinins from kininogen, induced by an infusion of bacterial lipopolysaccharide (LPS) in anesthetized, ventilated 20-kg pigs. The LPS was given IV in a dose of 5 /xg/kg/h for 8 hours. The plasma kallikrein inhibitor aprotinin, 537 pmo\, was given IV during 8 hours, resulting in plasma levels above 10 ^mol/L. Ten animals (SA) received LPS and aprotinin and ten randomized controls (SC) received LPS and saline. Kinin-containing kininogen was determined on the basis of the amount of kinin releasable in plasma samples by incubation with trypsin. Kininogen decreased to 58% ± 4% of the baseline value without any difference between groups. This may indicate participation of other processes than degradation by plasma kallikrein in the decrease of kininogen. Arterial blood pressure was higher at 7 hours in the SA animals than in the SC group (101% ± 11% vs. 68% ± 8%; mean ± SEM; p = 0.026). Fibrin monomer and C3a<*,Arg plasma levels were attenuated by aprotinin treatment. These findings underscore the important role of the contact system in LPS shock.BACTERIAL LIPOPOLYSACCHARIDE (LPS) is regarded as one of the causative agents of gram-negative sepsis and has been demonstrated to activate the contact phase of the intrinsic blood coagulation cascade in vitro.
1,2Arterial hypotension is induced by LPS in many species of experimental animals. Both the contact and the complement systems have been found to be activated in patients with septic shock.
3Activation of the contact system of blood coagulation ( Fig. 1) occurs as reciprocal activation of plasma kallikrein and Hageman factor (factor XII) in the presence of a negatively charged surface and high molecular weight kininogen (HMr kininogen) as cofactors. The potent hypotensive oligopeptide bradykinin has been implicated in the pathophysiology of shock.9 Decreased kininogen and prekallikrein concentrations 10 and elevated kinin levels 11 in plasma have been repeatedly described in experimental LPS shock and in patients with septic shock. Using a specific kinin receptor antag- onist it was demonstrated that kinins mediate LPSinduced arterial hypotension in rats.
12According to these results generation of active plasma kallikrein by contact system activation and subsequent release of bradykinin could play an important role in the pathophysiology of LPS-induced shock. To test this hypothesis we investigated whether in vivo inhibition of plasma kallikrein with aprotinin, a plasma kallikrein inhibitor, 13 would block or attenuate the effect of LPS on blood pressure and the concentration of uncleaved kininogen in pigs. Further questions concerned the effect of aprotinin on LPS-induced respiratory failure and on activation of the complement and coagulation systems.
MATERIALS AND METHODSMiniature pigs (Medical Service GmbH, Munich) with a body weight ranging from 18.0 to 22....