AJP - Regulatory, Integrative and Comparative Physiology, Vol 259, Issue 1 133-R138, Copyright © 1990 by American Physiological Society
Halothane sensitivity of young pigs in vivo and in vitro
R. S. Fay and E. M. Gallant
Department of Veterinary Biology, University of Minnesota, St. Paul 55108.
Piglets less than 8 wk of age that are known by genotype to be malignant
hyperthermia-susceptible (MHS) do not usually develop characteristic
hyperthermia and limb muscle rigidity in response to a brief halothane
exposure (5 min of 3%). To determine whether a malignant hyperthermia (MH)
episode could nevertheless be provoked by a more rigorous challenge, both
genetically MHS (Pietrain) and normal (Yorkshire) 5-wk-old piglets were
exposed to a combined halothane-succinylcholine challenge. Only two of
eight MHS piglets developed limb rigidity; however, all MHS piglets (and no
normal piglets) developed clinical signs of MH episode initiation during
the 30-min challenge. Temperatures rose from 37.4 to 38.6 degrees C in MHS
piglets while falling slightly in normal piglets. In MHS piglets, venous pH
fell from 7.46 +/- 0.02 to 6.88 +/- 0.07, PVCO2 rose from 36 +/- 2 to 126
+/- 17 mmHg, and plasma concentration of K+ rose from 4.0 +/- 0.1 to 7.1
+/- 0.6 mM, whereas all values remained stable in normal piglets. Muscles
removed from the same piglets before the halothane-succinylcholine
challenge were exposed to halothane in vitro. The muscles from genetically
MHS piglets responded to halothane with characteristic depression of
tetanic tension and prolonged tetanus relaxation time but did not develop
halothane-induced contractures. We conclude that, in the absence of either
halothane-induced limb rigidity or in vitro contractures, these young
animals were still susceptible to potentially fatal MH episodes on exposure
to appropriate triggering agents. The MH defect is apparently partially
masked in piglets and expressed fully only in older pigs.
