Induction of a pale, soft, exudative-like myopathy and sudden death in pigs by injection of anterior pituitary extract.

Abstract

Yorkshire pigs, 60 days old, were used to determine whether pale, soft, exudative (PSE) muscle and the porcine stress syndrome (PSS) could be induced by prolonged injections of desiccated porcine pituitary powder (PP). Three barrows and three ovariectomized gilts, negative for PSS by the halothane and CPK test, were assigned to each of the following groups: (1) control saline; (2) 50 mg of PP and (3) 100 mg of PP in saline. Injections were given intramuscularly in split doses, daily for 8 weeks. At 4 weeks, the level of PP was doubled. At 4 weeks, one pig of group 3 died, and by 8 weeks one pig of group 2 and two other pigs of group 3 died after displaying typical signs of PSS. Animals were anesthesized before exsanguination, and carcasses were held at room temperature. At time 0 postmortem PP-injected pigs had lower (P<.05) longissimus muscle pH, higher (P<.05) carcass temperature, lower (P<.01) muscle glycogen, higher (P<.001) muscle lactate and lower (P<.001) muscle creatine phosphate than saline-injected (control) pigs; whereas, muscle G-6-P tended to be higher (P<.1) in the PP-injected animals than in the control pigs, and muscle adenosine 5'-triphosphate (ATP) levels were similar in all treatments. PP-injection increased the rate of longissimus muscle postmortem glycolysis as shown by more rapid pH decline and ATP depletion and more rapid lactate accumulation. Hunter L and transmission value (sarcoplasmic protein solubility) of longissimus muscle indicated that the PP-injected pigs also displayed poorer quality muscle than the control pigs. Blood levels of glucose and lactate throughout the treatment period indicated that PP increased the general metabolic rate. Blood creatine phosphokinase (CPK) was also elevated by PP between 4 and 6 weeks of treatment. On the basis of visual appraisal of the longissimus muscle, none of six pigs in group 1, three of five pigs in group 2 and one of three pigs in group 3 displayed PSE musculature. The results indicate that prolonged injections of pituitary extract induced a PSE-like myopathy and sudden death, preceded by symptoms of PSS.