Effects of Acute Asphyxia and Deep Hypothermia on the State of Binding of Lysosomal Acid Hydrolases in Canine Cardiac Muscle

Abstract

The amount and state of binding of three lysosomal acid hydrolases, acid phosphatase, cathepsin, and β-glucuronidase, were studied in canine cardiac muscle following severe asphyxia and deep hypothermia. The studies were done on adult mongrel dogs anesthetized with sodium pentobarbital. Asphyxia was produced by tracheal occlusion, and was maintained until the onset of cardiac arrest (6 to 10 min). Hypothermic conditions were achieved by placing the heart on partial bypass through a heat exchanger. The heart was cooled to 6 to 10°C and held at this temperature for 30 min while circulation and respiration were maintained by artificial means. Control dogs were subjected to similar surgical procedures. Immediately following the experiments, the whole hearts were removed, cooled to 0 to 4°C, homogenized, and fractionated into supernatant and lysosomal fractions. The levels of bound and free acid hydrolases were estimated in the whole homogenates and fractions. Asphyxia produced a large shift of acid hydrolase activity from a bound form to a free form, as evidenced by elevated ratios of free to bound activity in the whole homogenates and elevated ratios of supernatant to lysosomal activity with respect to the fractions. Hypothermia did not alter the binding status of the lysosomal enzymes. These findings suggest that lysosomal enzymes play a major role in asphyxic damage to the heart.