Enhanced lysosome fragility in the anoxic perfused guinea pig heart: Effects of glucose and mannitol

Abstract

Guinea pig hearts were perfused under aerobic and anoxic conditions in the presence and absence of glucose or mannitol. Samples of the coronary perfusate were collected and assayed for creatine phosphokinase (CPK), hydroxybutyrate dehydrogenase (HBDH), leucyl-β-naphthylamidase (LBN) and lysosomal enzyme activities. After various periods of perfusion samples of left ventricle were homogenized and the specific activities (mu/mg protein) of N-acetyl-β-glucosaminidase, N-acetyl-β-galactosaminidase, β-glucuronidase and cathepsin C were determined. Estimates of lysosomal integrity were made from measurements of the latency and sedimentability of the marker enzymes. In control aerobic studies, with or without glucose or mannitol, there was an initial wash-out of CPK, HBDH and LBN with no further enzyme release for up to 6 h. The specific activities and the latency and sedimentability values of the lysosomal enzymes in cardiac homogenates were generally unaffected by aerobic perfusions. In contrast, during anoxic perfusions in the absence of glucose large amounts of CPK, HBDH and LBN were released into the coronary perfusate. The latency and sedimentability of each of the lysosomal enzymes was considerably decreased as a result of anoxic perfusion indicating enhanced lysosome fragility. These changes were significant after 30 min and progressed with the duration of anoxia. The specific activities of the lysosomal enzymes were significantly increased after 6 h anoxic perfusion. Inclusion of glucose in the anoxic perfusion medium did not prevent the release of CPK, HBDH and LBN in the early stages of anoxia but a reduction in myocardial enzyme release was observed in the later stages. The presence of glucose considerably delayed the onset of lysosomal membrane labilization but caused further increases in the specific activities of three of the acid hydrolases. Equimolar concentrations of mannitol had a limited effect on lysosome stability indicating that the protective effect of glucose was mainly due to its metabolic action.