The relationship between plasma epinephrine concentration and the activity of the calpain enzyme system in porcine longissimus muscle.

The relationship between plasma epinephrine and postmortem activity of the calpain system in porcine longissimus muscle was investigated. Two groups of Large White pigs were continuously infused intravenously with either placebo (control) or epinephrine (treated) at a rate of .15 micrograms.kg-1.min-1 for a period of 1 wk before slaughter. Samples of longissimus muscle were taken at 0, 1, 2, 4, 8, 24, 48, and 192 h (t0 to t192) after slaughter and immediately snap-frozen in liquid nitrogen for subsequent analysis of mu-calpain, m-calpain, and calpastatin activity. Epinephrine infusion had no effect on the activities of mu- and m-calpain at t0. Calpastatin activity at t0 was increased (P < .01) in treated pigs by 97%. The ratio of total calpain:calpastatin activity at t0 was reduced (P < .01) in treated pigs. The activity of mu-calpain decreased rapidly after slaughter, irrespective of treatment, dropping to less than 10% of the initial activity within 8 h. The activity of m-calpain also decreased over the first 8 h, although the rate of decrease was less (P < .05) in treated pigs. Consequently, m-calpain activity remained greater in treated pigs compared with controls throughout the period normally associated with tenderization. Postmortem values for calpastatin activity tended to be highly variable, with activities being similar between control and treated pigs within 1 h after slaughter. Over the entire 192 h sampling period, calpastatin activity decreased (P < .001), although the effect was independent of treatment. In general the results imply that variations in plasma epinephrine concentrations, which may naturally occur as part of the stress response, perturb the calpain enzyme system.