title: Developmental changes in diaphragm muscle function in the preterm and postnatal lamb.
abstract: BACKGROUND
  The preterm diaphragm is structurally and functionally immature, potentially contributing to an increased risk of respiratory distress and failure. We investigated developmental changes in contractile function and susceptibility to fatigue of the costal diaphragm in the fetal lamb to understand factors contributing to the risk of developing diaphragm dysfunction and respiratory disorders. We hypothesized that the functional capacity of the diaphragm will vary with maturational stage as will its susceptibility to fatigue.
  
  
  METHODS
  Lambs were studied at 75, 100, 125, 145, 154, 168, and 200 days postconceptional age (term = 147 days). Lambs were euthanized (sodium pentobarbitone, 100 mg/kg) either at delivery or immediately prior to post-mortem for postnatal lambs. Contractile function was assessed on longitudinal strips of intact muscle fibers and the remaining tissue frozen in liquid nitrogen for analysis of myosin heavy chain (MHC) mRNA expression and protein content.
  
  
  RESULTS
  Fetal development of diaphragm function was characterized by a significant increase in maximum specific force, increased susceptibility to fatigue, reduced twitch contraction times, and a progressive increase in MHCI and MHCII protein content. Postnatally, there was a progressive decrease in the susceptibility to fatigue that coincided with an increase in the MHC I:II protein ratio.
  
  
  CONCLUSIONS
  These data indicate that the functional capacity of the diaphragm varies with maturational age and may be an important determinant of the susceptibility to preterm respiratory failure.
authors: School of Anatomy, Physiology, and Human Biology, The University of Western Australia, Crawley, Western Australia, Australia.
authors: T
authors: T
authors: Lavin
authors: Y
authors: Y
authors: Song
authors: A J
authors: AJ
authors: Bakker
authors: C J
authors: CJ
authors: McLean
authors: W A
authors: WA
authors: Macdonald
authors: P B
authors: PB
authors: Noble
authors: C A
authors: CA
authors: Berry
authors: J J
authors: JJ
authors: Pillow
authors: G J
authors: GJ
authors: Pinniger
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D003964:Diaphragm / Q000196:embryology* / Q000378:metabolism / Q000502:physiology; D005333:Fetus / Q000196:embryology* / Q000378:metabolism / Q000502:physiology; D020869:Gene Expression Profiling; D066298:In Vitro Techniques; D009119:Muscle Contraction / Q000502:physiology*; D024510:Muscle Development / Q000235:genetics / Q000502:physiology*; D018763:Muscle Fatigue / Q000502:physiology*; D018995:Myosin Heavy Chains / Q000235:genetics; D012333:RNA, Messenger / Q000032:analysis*; D012132:Respiratory Muscles / Q000196:embryology / Q000378:metabolism / Q000502:physiology; D012756:Sheep
chemical_list: D012333:RNA, Messenger; D018995:Myosin Heavy Chains