Cytophotometry of post mortem glycogenolysis in different histochemical types of muscle fibres of the pig.

Serial transverse sections of porcine longissimus dorsi muscle (18 pigs, 50 to 178 kg live weight) were reacted for NAD tetrazolium reductase and ATPase at pH 9.4, and for glycogen with the periodic acid-Schiff (PAS) reaction. Three histochemical types of muscle fibre were identified; (1) strong ATPase and weak NADH oxidative activity; (2) strong ATPase and intermediate NADH oxidative activity; and (3) weak ATPase and strong NADH oxidative activity. Immediate post mortem samples from one side of each animal were compared with a later post mortem sample from the other side by measuring the absorbance of PAS-stained glycogen at 570 nm with a microscope photometer. Later post mortem absorbance was expressed as a percentage of immediate post mortem absorbance in each category of muscle fibre in order to compensate for distributional error and different starting levels of glycogen. Muscle fibres with weak ATPase and strong NADH oxidative activity showed a progressive decrease in absorbance of PAS-stained glycogen post mortem. In some animals, fibres with strong ATPase and intermediate or weak NADH oxidative activity showed an initial post mortem increase in absorbance of PAS-stained glycogen which was then followed by a progressive decrease. The maximum rates of decrease in absorbance in the three fibre types did not differ to any great extent.