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. Tw o groups of Large White pigs were continuously infused intravenously w ith either placebo (control) or epinephrine (treated) at a rate of .15 mu g . 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 (t(0) to t(192)) after slaughter and immediately snap-frozen in liquid nitrogen for subsequent analysis of mu-calpain, m-calpain, and calpas tatin activity. Epinephrine infusion had no effect on the activities o f mu- and m-calpain at t(0). Calpastatin activity at t(0) was increase d (P < .01) in treated pigs by 97%. The ratio of total calpain:calpast atin activity at t(0) was reduced (P < .01) in treated pigs. The activ ity of mu-calpain decreased rapidly after slaughter, irrespective of t reatment, dropping to less than 10% of the initial activity within 8 h . The activity of m-calpain also decreased over the first 8 h, althoug h the rate of decrease was less (P < .05) in treated pigs. Consequentl y, m-calpain activity remained greater in treated pigs compared with c ontrols throughout the period normally associated with tenderization. Postmortem values for calpastatin activity tended to be highly variabl e, with activities being similar between control and treated pigs with in 1 h after slaughter. Over the entire 192 h sampling period, calpast atin activity decreased (P < .001), although the effect was independen t 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.