Porcine malignant hyperthermia: false negatives in the halothane test

Area of Science:

• Veterinary Science
• Animal Genetics
• Pharmacology

Background:

• Malignant hyperthermia (MH) is a genetic disorder affecting skeletal muscle.
• Pietrain pigs are often used in research due to their susceptibility to MH.
• The halothane challenge test is a common method for diagnosing MH susceptibility.

Purpose of the Study:

• To investigate why some genetically MH-susceptible Pietrain pigs do not exhibit muscle rigidity during halothane challenge tests.
• To analyze the in vitro muscle cell responses to halothane in pigs that are genetically susceptible but phenotypically negative for MH.

Main Methods:

• Purebred Pietrain pigs, presumed homozygous for MH susceptibility, underwent a 3% halothane challenge test.
• Muscle biopsy specimens were obtained from three halothane-negative, genetically susceptible pigs.
• In vitro analysis of muscle cell bundles was performed, monitoring mechanical responses to electrical stimulation and halothane exposure.

Main Results:

• Six percent of pigs expected to be MH susceptible did not develop muscle rigidity in vivo.
• In vitro analysis revealed that muscle bundles from halothane-negative, genetically susceptible pigs showed impaired tetanic tension, slowed relaxation, and contractures upon halothane exposure.
• These in vitro responses were similar to those of halothane-positive MH-susceptible pigs.

Conclusions:

• In vivo muscle rigidity during halothane challenge is not solely dependent on the presence of a halothane-sensitive abnormality in skeletal muscle.
• False negative results can occur in a small percentage of genetically MH-susceptible pigs, even with recommended testing techniques.
• Further investigation into the mechanisms underlying MH expression in pigs is warranted.