Effect of age and cold exposure on morphofunctional characteristics of skeletal muscle in neonatal pigs.
Muscular changes accompanying and/or promoting the rapid postnatal improvement of the thermogenic efficiency of shivering were investigated in piglets. Animals were obtained at birth or killed after 5 days at thermoneutrality (34-30 degrees C) or in the cold (24-15 degrees C), to stimulate intense shivering thermogenesis. Fast-twitch-glycolytic (longissimus lumborum) and slow-twitch-oxidative (rhomboid) muscles were prepared for electron microscopic examination and chemical measurements. Muscle-specific changes in energy stores and metabolism were observed after birth, including the switch from glycogen to lipids and variation of the lactate/pyruvate ratio corresponding to the progressive acquisition of the metabolic type of the mature muscles. There was major age-related and/or cold-induced development of the structures involved in excitation-contraction coupling (triadic profiles, +80% in the cold), oxidative metabolism (number of lipid droplets, +81% with age in the cold; number of mitochondria, +29% with age or cold; surface of mitochondrial inner membranes, +18% with age and +32% in the cold) and contraction potential (myofibril volume, +62% with age). In contrast, neither age nor cold affected capillary volume density and capillary-to-fibre ratio. The observed changes reflect the immaturity and remarkable plasticity of piglet skeletal muscle and are likely to underlie its enhanced capacity for shivering thermogenesis after birth.
Herpin
Patrick
P
Unité Mixte de Recherches sur le Veau et le Porc, INRA 35590 St-Gilles, France. herpin@st-gilles.rennes.inra.fr
Lossec
Gaëlle
G
Schmidt
Isabelle
I
Cohen-Adad
Frédérique
F
Duchamp
Claude
C
Lefaucheur
Louis
L
Goglia
Fernando
F
Lanni
Antonia
A
D000273:Adipose Tissue / Q000502:physiology; D000367:Age Factors; D000818:Animals; D000831:Animals, Newborn; D001833:Body Temperature Regulation / Q000502:physiology*; D002196:Capillaries / Q000502:physiology / Q000648:ultrastructure; D003080:Cold Temperature; D004734:Energy Metabolism / Q000502:physiology; D008854:Microscopy, Electron; D008928:Mitochondria / Q000502:physiology / Q000648:ultrastructure; D009119:Muscle Contraction / Q000502:physiology; D018656:Muscle Fibers, Fast-Twitch / Q000502:physiology / Q000648:ultrastructure; D018482:Muscle, Skeletal / Q000098:blood supply / Q000166:cytology / Q000502:physiology*; D009210:Myofibrils / Q000502:physiology / Q000648:ultrastructure; D012768:Shivering / Q000502:physiology; D013552:Swine