VARIABILITY OF ENERGY-METABOLISM AND NUCLEAR T-3-RECEPTORS WITHIN THESKELETAL-MUSCLE TISSUE OF PIGS DIFFERENT WITH RESPECT TO THE HALOTHANE GENE

Energy metabolism of skeletal muscle tissue of pigs growing from appro ximately 12 to 18 kg (12 homozygous halothane negative, HH; 16 heteroz ygotes, Hh; 17 homozygous halothane susceptible, hh) was measured in v ivo using P-31 nuclear magnetic resonance (NMR) spectroscopy. Data for intracellular pH, phosphocreatine (PCr), phosphomonoesters (PME), and ATP were analyzed by canonical discriminant analysis, an artificial n eural network approach, and analysis of variance. Within the hh pigs, two subpopulations could be distinguished before the application of ha lothane treatment. Some of the hh pigs had a high PME concentration in the biceps femoris muscle (hh(pme+)), whereas others had a low concen tration (hh(pme-)) (2.18 +/- .12 for hh(pme+) vs 1.68 +/- .12 mM for h h(pme-), P <.004). The hh(pme+) pigs were statistically different from HH pigs for pH (P <.03), PME (P <.004), and PCr(P <.008) before halot hane treatment. The hh(pme-) pigs were not different from the Hh and H H pigs with respect to PME when measured before halothane treatment (P >.05). However, intracellular pH (P <.03) and PCr (P < .008) of the h h(pme-) pigs were different from those of KH pigs (7.15 vs 7.19 for pH and 38.7 vs 35.1 for PCr, respectively). When combining intracellular pH, PME, and PCr within a canonical discriminant analysis, all were m easured before halothane treatment, Hh pigs were found to be different from HH pigs (Mahalanobis distance different from zero, P <.02). In a second experiment, growth rate, depth of longissimus muscle, and maxi mal binding capacity of nuclear T-3-receptors of skeletal muscle tissu e were different (P <.05, P < .002, and P <.02, respectively) among pi gs selected from the same genetic lines. Of the variability in depth o f the longissimus muscle, 22% was explained by variability in maximal binding capacity of nuclear T-3-receptors. These results, if confirmed with a large number of pigs, might open new possibilities for selecti on procedures for leanness because, with respect to halothane suscepti bility, a shift between genotypic and phenotypic variability was obser ved.