Clinical Biochemistry of Domestic Animals (Sixth Edition) - UMK ...

IV. Toxins Affecting Skeletal and Cardiac Muscle
827
IV . TOXINS AFFECTING SKELETAL AND
CARDIAC MUSCLE
The clinical signs of weakness, dysmetria, and incoordination
suggest not only the possibility of neurological disease
but also skeletal muscular or cardiovascular disease.
Acute toxicity of skeletal or cardiac muscle ( Table 27-3 )
can be detected by elevations in serum creatine kinase
(CK) ( Cardinet, 1997 ). This dimeric enzyme catalyzes
the reversible reaction, phosphocreatine ADP
creatine ATP, and has three isoenzyme types: CK 1 , CK 2 ,
and CK 3 . CK 1 is found in brain, peripheral nerves, cerebrospinal
fluid, and viscera, but it is not found in serum during
neurological disease. CK 2 is found in cardiac muscle and
minute amounts in skeletal muscle. CK 3 is found in cardiac
and skeletal muscle. CK plasma half-life is short and
is considered to be specific for muscle when hemolysis,
elevated bilirubin, muscle fluid contamination during venipuncture,
and dilution of CK inhibitors during sample processing
can be excluded. When injury is not progressive,
CK elevations maximize within 6 to 12 h and return to normal
within 24 to 48 h. Continuing necrosis can result in
persistent elevation.
Cardiac troponin T and I have been demonstrated to be
sensitive and specific biomarkers of cardiac injury in dogs
and laboratory animals ( O’Brien, 2006 ; O’Brien et al. ,
2006 ). Cardiac troponins have been demonstrated to correlated
with myocardial injury in the dog, cat, and horse
and may provide a more specific antemortem method of
detecting myocardial compromise secondary to toxicosis
in these species (Herndon, 2002; Oyama and Sisson, 2004 ;
Schwarzald et al. , 2003 ).
As discussed previously, LDH 5 is the principal isoenzyme
in skeletal muscle and erythrocytes. LDH activity
is tissue nonspecific, but necroses of muscle, liver, and
hemolysis are the major sources for elevations of serum
activity. Necrosis of skeletal muscle may result in release
of myoglobin and potassium resulting in myoglobinemia
and hyperkalemia. Myoglobinuria, detectable by urinalysis,
may induce secondary nephrotoxicity.
TABLE 27-3 Toxins Affecting Cardiac and Skeletal Muscle
Toxins Disease Onset Geography Species Affected
Cardiac glycosides Acute Worldwide All
Cassia occidentalis (Coffee senna) Acute Worldwide B, Cp, O, P
Cantharidin (blister beetle) Acute US E
Catecholamines Acute All
Eupatorium rugosum (white snakeroot) Chronic US B, E
Fluoroacetate Acute AUS, S AFR All
Gossypol (cottonseed) Chronic Worldwide P, B, Cn
Hypercalcemia Chronic Worldwide All
Iron Acute Worldwide P
Karwinskia humboldtiana (coyotillo) Acute to chronic MEX, TX Cp, O
Lantana camara Chronic AFR, AUS, MEX, US B, E, O
Metals (As, Bi, Cd, Hg, Pb, Tl) Acute to chronic Worldwide All
Methylxanthines (caffeine, theophyl-line,
theobromine)
Acute Worldwide Cn
Monensin Acute to chronic Worldwide B, E, Cp, O, P
Nephrotoxins (uremia, see text) Chronic All
Persea americana (avocado) Acute Worldwide B, Cp, E, O
Phalaris Acute Worldwide B, E, O
Phosphorus Acute Worldwide All
Potassium Acute to chronic Worldwide All
Pteridium aquilinum (Bracken fern) Acute to chronic Worldwide B, Cp, E, O, P
Quinolizidine alkaloids (Lupinus spp.) Chronic Worldwide B, O
Vicia villosa (hairy vetch) Chronic Worldwide B, E
Abbreviations: B, bovine; Cn; canine; Cp, caprine; E, equine; F, feline; O, ovine; P, porcine.