G. Mitchell

Porcine Stress Syndromes

Publisher Summary This chapter discusses that porcine stress syndrome (PSS) is characterized by acute death induced by natural stressors—such as—transport, high ambient temperature, exercise, fighting, service, and parturition. Malignant hyperthermia (MH) is a pharmacogenetic disease. Identification of pigs susceptible to any of the stress syndromes is of great importance. The chapter discusses that serological tests have focused on the measurement of serum enzymes. Hematological tests have analyzed platelet function, blood groups, and erythrocyte fragility in attempts to find a predictive test. In general, the rationale has promised much, but the results have been disappointing. In man, susceptibility to MH is well correlated with clinical myopathies. There is no doubt that sympathetic nerve activity associated with stress causes the release of adrenaline and nonadrenaline. It is well recognized that thyroid hormones regulate tissue metabolic rates. Hypermetabolism of tissues and hyperthermia are characteristic of PSS and MH, and a priori link between thyroid hormone activity and stress seems likely. The chapter discusses that although it is possible for clinically normal pigs to develop stress syndromes, the data presented here argue that pigs most likely to develop MH and PSS have a “homozygote” genetic defect involving a single gene. A whole range of responses to stress or drugs can, therefore, be envisaged and breed variations and the difficulty of finding unequivocal predictive tests all can be accounted for by variation in the severity of the inherited defect.

A halothane-induced biochemical defect in muscle of normal and malignant hyperthermia-susceptible Landrace pigs.

Muscle adenosine triphosphate (ATP), glucose-6-phosphate, phosphocreatine, and pH were measured in nine malignant hyperthermia (MH)-susceptible and 14 MH-resistant Landrace pigs. Muscle biopsies were taken before (under barbiturate anesthesia) and after exposure to halothane. When compared to levels during barbiturate anesthesia, exposure to halothane had no immediate effect on muscle ATP levels in either MH-susceptible or -resistant pigs. However, once malignant hyperthermia developed in susceptible pigs ATP levels decreased significantly. In both susceptible and resistant pigs halothane increased muscle glucoses-phosphate and decreased muscle phosphocreatine and pH significantly below control levels observed during barbiturate anesthesia. In susceptible pigs these changes were significantly more marked than were the changes produced in resistant pigs. These data indicate that the effect of halothane on muscle metabolism is similar in both MH-resistant and -susceptible pigs. The results suggest that the effect of halothane is to inhibit aerobic metabolism by preventing mitochondrial dehydrogenation of pyruvate. Inhibition is complete in susceptible pigs but only retarded in resistant pigs. In susceptible pigs the consequent lactacidosis, hyperthermia, and reduction in ATP synthesis contribute to the development and maintenance of rigidity.

Diagnostic value of serum creatine phosphokinase activity for the porcine malignant hyperthermia syndrome.

&NA; Serum creatine phosphokinase (CPK) activity was measured in 10 German Landrace pigs from 11 to 28 weeks of age. A pronounced age dependence of serum enzyme activity was observed, peak activity occurring at 19 weeks of age. At the end of the growth period, when the pigs were challenged with halothane to detect the malignant hyperthermia syndrome, 3 pigs were found to be susceptible. Significant increases in the serum enzyme levels in the susceptible pigs were observed only at 11 and 28 weeks of age. Serum enzyme levels measured during the rapid phase of growth could not be used to predict the malignant hyperthermia syndrome. Elevated serum CPK levels were also observed in two litters of Large White and Landrace x Large White pigs, breeds known to be stress‐resistant. No pigs in these litters were susceptible to halothane, even though CPK levels were similar to those of the German Landrace pigs. The results indicate that serum CPK levels can be used as evidence of predisposition to the malignant hyperthermia syndrome but cannot be relied on as a single ultimate test.

Muscle Fibre Type, Fibre Diameter and pH1 Values of M. Longissimus Dorsi of Normal, Malignant Hyperthermia- and Pse-Susceptible Pigs

SUMMARY Landrace pigs susceptible to malignant hyperthermia (MH/PSE) and to the pale, soft, exudative muscle syndrome (PSE) exhibited similar muscle fibre type compositions to normal Landrace pigs. Mean muscle fibre diameters were not significantly different between the three groups of pig. The intermediate oxidative fibres of MH/PSE pigs tended to be larger than the corresponding fibre type of PSE and normal pigs. The scatter of muscle fibre diameter was greatest in normal and MH/PSE pigs. It is concluded, in agreement with another recent report, that altered muscle fibre type is not the primary basis of susceptibility to MH or PSE.

Some muscle and growth characteristics of pigs susceptible to stress.

SUMMARY Landrace pigs can be divided into those which are sensitive to halothane and develop pale, soft, exudative pork (PSE) post mortem (MH/PSE), those which are resistant to halothane but develop PSE (PSE) and those resistant to halothane and PSE (normal). Muscle characteristics of PSE and normal pigs are indistinguishable under thiopentone anaesthesia and differ only in pH after slaughter. Muscle from MH/PSE pigs has significantly higher glucose-6-phosphate levels and lower phosphocreatine under thiopentone anaesthesia than PSE and normal muscle. Exposing MH/PSE pigs to halothane anaesthesia exaggerates these differences. PSE pigs showed decreased daily liveweight gain compared with MH/PSE pigs while normal pigs had the greatest daily gain.

Effects of potassium, procaine and dantrolene on the calcium-dependent and "basal" ATPase activities of sarcoplasmic reticulum of skeletal muscle.

1. 1. Potassium ions, in the presence of 5 mM oxalate, stimulated the Ca2+-dependent ATPase activity of sarcoplasmic reticulum fragments (SRF) of rat gastrocnemius muscle. Half-maximal stimulation occurred with 20 mM KCl. A similar stimulation was observed when oxalate was omitted. 2. 2. Procaine (1–5 mM) inhibited the Ca2+-dependent ATPase in the presence and absence of potassium and of oxalate. 3. 3. Dantrolene sodium (8.9 μM) stimulated slightly the Ca2+-dependent ATPase under conditions in which procaine inhibited the enzyme. 4. 4. “Basal” ATPase of SRF was not affected by potassium, procaine or dantrolene.

Age dependent variation of serum creatine phosphokinase levels in pigs

Infolge Muskeltätigkeit steigt bekanntlich der Creatin-Phosphokinase-Spiegel (CPK) im Serum. Es wird nun eine Abhängigkeit des Serum-CPK-Wertes vom Alter festgestellt. Es ist daher wichtig, nichtspezifische Ursachen eines gesteigerten CPK-Spiegels auszuschalten, ehe eine Diagnose der Muskelerkrankung gestellt wird.