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Diagnostic Ultrasound Imaging of Mouse Diaphragm Function
07:12

Diagnostic Ultrasound Imaging of Mouse Diaphragm Function

Published on: April 21, 2014

Hypothyroidism alters diaphragm muscle development

G C Sieck1, L E Wilson, B D Johnson

  • 1Department of Anesthesiology, Mayo Clinic and Foundation, Rochester, Minnesota 55905, USA. gcs@Siecklab.Mayo.edu

Journal of Applied Physiology (Bethesda, Md. : 1985)
|November 1, 1996
PubMed

Insights

Hypothyroidism in developing rats alters myosin heavy chain (MHC) expression in diaphragm muscles, leading to reduced muscle force and slower shortening velocity. These changes in MHC isoforms do not fully explain the observed alterations in diaphragm contractile properties.

Area of Science:

  • Physiology
  • Developmental Biology
  • Endocrinology

Background:

  • Hypothyroidism affects muscle development and function.
  • Myosin heavy chain (MHC) isoforms are critical for muscle contractility.
  • Understanding these impacts during development is crucial for pediatric endocrinology and muscle physiology.

Purpose of the Study:

  • To investigate the effects of hypothyroidism on rat diaphragm muscle (Dia) MHC isoform expression, force production, fatigability, and shortening velocity during postnatal development.
  • To determine if changes in MHC isoform expression correlate with alterations in diaphragm contractile function.

Main Methods:

  • Hypothyroidism induced in pregnant rats using propyl-thiouracil.
  • Analysis of MHC isoforms in diaphragm muscle via SDS-PAGE and densitometry.
  • In vitro assessment of isometric force, fatigue resistance, and unloaded shortening velocity of the diaphragm.

Main Results:

  • Hypothyroid diaphragm muscles showed increased MHC-slow and decreased adult fast MHC isoform expression.
  • Neonatal MHC isoform expression persisted in hypothyroid muscles until day 28.
  • Reduced maximum specific force (P0), increased fatigability, and slower maximum unloaded shortening velocity (V0) were observed in hypothyroid diaphragm muscles at all ages.
  • Hypothyroidism-induced changes in MHC isoform expression did not fully account for the observed deficits in diaphragm contractile properties.

Conclusions:

  • Hypothyroidism significantly alters MHC isoform composition and contractile function in the developing rat diaphragm.
  • The relationship between MHC isoform expression and diaphragm contractile properties is complex and not fully explained by isoform shifts alone.
  • Further research is needed to elucidate the mechanisms underlying hypothyroid myopathy in developing skeletal muscle.

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