ISCHAEMIA-REPERFUSION INJURY IN SKELETAL MUSCLES OF MAST CELL DEFICIENT MICE

Susan Bortolotto, Wayne Morrison, Aurora Messina, Bernard O'Brien Institute of Microsurgery, and Department of Surgery, The University of Melbourne and St Vincent's Hospital Melbourne, 42 Fitzroy St., Fitzroy 3056, Vic.

Background: Ischaemia-reperfusion injury (IRI) to skeletal muscle is a significant cause of morbidity following traumatic injury and is a major complication following replantation of severed limbs and surgical flap transfer. We have made novel observations that implicate mast cells, in the pathogenesis of IRI in skeletal muscle and this may have much broader implications for the under standing of IRI in general.

Objectives: To study IRI in skeletal muscles of mast cell deficient mice and their littermate controls.

Methods: Under general anaesthetic, tourniquet hind limb ischaemia was induced in mice by an elastic rubber band placed as high as possible on the right thigh. This results in total hind limb ischaemia including the nerves and blood vessels. Ischaemic muscle temperature was monitored and maintained at 36°C and after 70 minutes the tourniquet was removed and the mice allowed to recover. Following twenty-four hours reperfusion mice were re-anaesthetised, the Gastrocnemius (mixed fast- and slow-twitch), Soleus (slow-twitch) and Extensor Digitorum Longus (EDL) (fast-twitch) muscles were removed and the outcome assessed by Nitro Blue Tetrazolium, Lactate Dehydrogenase (muscle viability) and morphometry (mast cell detail).

Summary: Muscle viability of mast cell deficient mice versus littermate controls was dependent on the type of muscle studied. Soleus muscle viability was 94% v/s 51%, Gastrocnemius was 81% v/s 34% and EDL was 75% v/s 23% in mast cell deficient and littermate controls respectively. Assay of residual muscle lactate dehydrogenase and histological examination of injured and contralateral muscles confirmed these data. These results were directly correlated to mast cell profile densities present in skeletal muscle sections. They indicate that mast cells play an important role in IRI of skeletal muscles.