PROTEASES AND CHEMICAL MEDIATORS IN 
ACUTE CORONARY OCCLUSION IN THE DOG 
H, J, Wilkens, R. Steger and N. Back' 
The possible significance of protease activation and 
release of vasoactive mediators in the pathogenesis of 
acute myocardial infarction following coronary occlu- 
sion in the unanesthetized dog was studied. Dogs were 
prepared under anesthesia with a loose ligature around 
the anterior descending branch of the left coronary 
artery. The ends of the ligature were exteriorized 
through the chest wall, and both the pericardial sac 
' and chest wall closed. After a 7-day recovery period, 
the ligatures were tightened suddenly and both physio- 
logic and biochemical parameters studied at frequent 
!| intervals prior to and during the acute phase of the oc- 
!| elusion and for 6-8 days thereafter. In all, 14 dogs have 
been studied to date; 7 saline treated control dogs and 
7 dogs that received a proteolytic enzyme inhibitor, 
TRASYLOL, 50,000 units/kg intravenously, just prior 
to coronary occlusion. Three control dogs died within 24 
I hours, while 2 drug-treated dogs died during the same 
time period. Control dogs evidenced more pain at the 
time of occlusion. Hematocrit values were higher in the 
control dogs from the 24-hour period. While prothrombin 
levels were decreased in both groups of dogs, Lee White 
clotting times were prolonged in the control dogs. A 
fibrinogen increase noted in the control dogs did not 
occur in the drug-treated dogs until 24 hours after 
occlusion. Initially euglobulin clot lysis times were not 
altered significantly but were shortened at 30 minutes 
in both groups. No blood kinin activity was detected 
in either group, although kininase activity was elevated 
in the control group. Kininogen decreases were evident 
in both groups from the 24-hour time period. These 
initial data encourage further study with this experi- 
mental model system. 
INTRODUCTION** 
Present evidence supports the concept that 
severe myocardial ischemia can cause ventric- 
ular arrhythmias leading to sudden death or 
serious pump failure.^ Alterations in carbo- 
hydrates, lipid, and protein metabolism, as well 
as changes in intracellular enzyme systems, 
have been reported in the ischemic state.- In- 
* Department of Biochemical Pharmacology, School of Pharmacy, 
State University of New York, Buffalo, New Yoi k. 
** Supported in part by USPHS Grants #HE-03487 and #HE- 
11492. 
creased lactic acid levels have been demon- 
strated in coronary sinus blood within seconds 
after coronary artery ligation.- -' This lowered 
pH provides a suitable milieu for activation of 
lysosomal proteases that are released by cell 
wall changes and autolysis. 
While the significance of these intracellular 
enzymes in the myocardial response to ischemia 
remains uncertain, their involvement in the 
pathologic process of infarction growth may be 
considered. In addition, recent studies have 
shown that only a slight lowering of blood pH 
results in the activation of plasma proteases 
and subsequent release of potent vasopeptides,'* 
in accordance with the scheme seen in Fig. 1. 
The interrelationship between the fibrinolysin 
and vasoactive polypeptide systems (Fig. 2) has 
been reviewed.'^' Evidence supports the partici- 
pation of kinins in the mechanism of spontan- 
eous pain during myocardial ischemia, and that 
in the initial phase of myocardial infarction, the 
kinins formed by protease action participate m 
the mechanism of collapse and shock. •'■'^ Bas- 
sange et al.*^ have identified a bradykinin poten- 
tiating peptide active in the coronary circula- 
tion following kinin administration. 
The present studies were undertaken to pro- 
vide a detailed integrated account of the role 
the protease and vasopeptide systems might 
play in the clinical sequence of acute myocardial 
ischemia. Use of protease inhibitors provides 
an additional tool for clarifying the role of pro- 
teases, and may yield information of possible 
therapeutic significance. 
METHODS 
Acute Coronary Occlusion 
Fourteen healthy dogs, anesthetized with in- 
travenous sodium pentobarbital, 35 mg/kg, 
were intubated to facilitate artificial respira- 
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