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.
Unité Mixte de Recherches sur le Veau et le Porc, INRA 35590 St-Gilles, France. herpin@st-gilles.rennes.inra.fr
Patrick
P
Herpin
Gaëlle
G
Lossec
Isabelle
I
Schmidt
Frédérique
F
Cohen-Adad
Claude
C
Duchamp
Louis
L
Lefaucheur
Fernando
F
Goglia
Antonia
A
Lanni
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