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Accelerated contractile function and improved fatigue resistance of calf muscles in newborn piglets with IUGR
1Institute of Sports Science, Friedrich Schiller University, D-07740 Jena, Germany.
Insights
Intrauterine growth restriction (IUGR) in piglets accelerates skeletal muscle contractile function despite reduced muscle mass. IUGR piglets exhibited enhanced specific muscle force and faster force recovery after blood flow restoration compared to normal weight controls.
Area of Science:
- Physiology
- Developmental Biology
- Muscle Biology
Background:
- Asymmetrical intrauterine growth restriction (IUGR) causes disproportionate muscle mass reduction.
- The impact of IUGR on skeletal muscle contractile function and tissue development remained unstudied.
Purpose of the Study:
- To investigate the effects of IUGR on skeletal muscle contractile function and tissue development in piglets.
- To compare isometric force output, specific muscle force, and muscle fiber type distribution between normal weight (NW) and IUGR piglets.
Main Methods:
- Isometric force output of hindlimb plantar flexors was measured in anesthetized NW and IUGR piglets.
- Blood supply was manipulated (normal, reduced, reestablished) and measured using colored microspheres.
- Muscle fiber type distribution, specific muscle force, glycogen content, and morphometric data were analyzed.
Main Results:
- Specific muscle force was significantly higher in IUGR piglets (6.1 N/g) compared to NW piglets (5.2 N/g).
- IUGR piglets showed a lower rate of force decrease during isometric contractions and near-complete functional recovery post-reperfusion.
- IUGR piglets exhibited an increased proportion of type I muscle fibers in specific hindlimb muscles.
Conclusions:
- Newborn IUGR piglets demonstrate accelerated skeletal muscle contractile function.
- IUGR influences muscle fiber type distribution, favoring type I fibers.
- Despite reduced mass, IUGR muscles exhibit enhanced specific force and functional resilience.
Abstract:
Asymmetrical intrauterine growth restriction is denoted by disproportional reduction of muscle mass compared with body weight reduction. However, effects on contractile function or tissue development of skeletal muscles were not studied until now. Therefore, isometric force output of serial-stimulated hindlimb plantar flexors was measured in thiopental-anesthetized normal weight (NW) and intrauterine growth-restricted (IUGR) 1-day-old piglets under conditions of normal, reduced (aortic cross clamping), and reestablished (clamp release) blood supply (measured by colored microspheres technique). Furthermore, muscle fiber type distribution was determined after histochemical staining, specific muscle force of the plantar flexors [quotient from absolute force divided by muscle mass (N/g)] was calculated, and glycogen content and morphometric data of the investigated muscles were estimated. Regional blood flow of hindlimb muscles was similar in NW (6 +/- 2 ml. min(-1). 100 g(-1)) and IUGR piglets (8 +/- 1 ml. min(-1). 100 g(-1)). Isometric muscle contractions induced a marked increase in regional blood flow of 4.1-fold in NW and 5-fold in stimulated hindlimb muscles of IUGR piglets (baseline blood flow). Specific force of NW piglet muscles (5.2 +/- 0.2 N/g) was significantly lower than IUGR piglet muscles (6.1 +/- 0.6 N/g; P < 0.05). Isometric muscle contractions (NW: 32.7 +/- 4.7 N; IUGR: 21.7 +/- 4.0 N) resulted in a higher rate of force decrease in the calf muscles of NW animals compared with IUGR piglets (8 +/- 2 vs. 3 +/- 1%; P < 0. 01). Functional restoration of contractile performance after hindlimb recirculation was nearly complete in IUGR piglets (98 +/- 1%), whereas in NW piglets a deficit of 9 +/- 3% was found (P < 0. 01). Muscle fiber type estimation revealed an increased proportion of type I fibers in flexor digitalis superficialis and gastrocnemius medialis in IUGR piglets (P < 0.05). These data clearly indicate that contractile function is accelerated in newborn IUGR piglets.