GENETIC VARIATION IN MITOCHONDRIAL RESPIRATORY METABOLISM IN AVIAN AND MAMMALIAN SPECIES.

Abstract

Comparative studies documented relationships between mitochondrial respiration and phenotype among genetically divergent animals. Broiler chickens' mitochondria ranked higher than layer chickens' for state 3 respiration (16.1 ± 0.4 μM O₂/mg protein/min), respiratory control ratio (3.5 ± 0.1) and ADP:O ratio (1.05 ± 0.01 μM ADP/μA O) utilizing succinate. Broilers yielded more (P < .05) mitochondrial protein than did layers (7.8 vs. 6.2 ± 0.2 mg/g hepatic tissue). Within-breed mitochondrial activity had no associations with chicken weight or egg production. C57BL/6J mice mitochondria had higher (P < .05) respiratory control ratios (4.06 vs. 3.78 ± 0.09), and C57BL/6J females higher state 3 respiration rates utilizing succinate (strain by sex interaction P < .01), than A/J or BALB/cJ mice mitochondria. BALB/cJ mitochondria had higher (P < .05) ADP:O ratios utilizing pyruvate than C57BL/6J mitochondria (1.58 vs. 1.46 ± 0.04 μM ADP/μA O). Rapid ATP synthesis rates of C57BL/6J female mice were associated generally with reproductive superiority. Inbred mouse body weight was not associated with mitochondrial respiration. Original data confirmed CB6F₁, but not CAF₁, hybrid mice were heterotic for postweaning growth. Hybridization increased (P < .05) mitochondrial mass, but did not enhance respiration. No association existed between growth heterosis and mitochondrial function in hybrid mice. Unexpected sexual dimorphism in mitochondrial respiration existed across mouse strains. Testosterone administration and orchiectomy confirmed female mice exhibited superior organelle activity. Mitochondrial ATP synthesis rates of Holstein cows correlated (+.30 to +.48) with milk production traits of cows and their dams suggested maternal breeding values for milk yield might be improved by considering mitochondrial effects. No breed differences in state 3 respiration (17.7 ± 0.6 μM O2/mg protein/min) or ADP:O ratio with succinate (1.17 ± 0.01 μM ADP/μA O) existed among Angus, Brangus and Hereford cows. Regression analyses of growth traits of cows and their relatives on mitochondrial parameters revealed mainly nonsignificant mitochondrial effects. Significant regression coefficients (-0.43 to -1.05) were found for some cattle growth traits regressed on ADP:O ratios. No mitochondrial complementation occurred between neutrally-combining animal strains. Complementation occurred in mitochondrial mixtures from females of mouse strains with positive combining ability exclusively. Cow mitochondrial mixtures had lower (P < .05) state 3 rates than predicted.