Interstitial space and collagen alterations of the developing rat diaphragm

Area of Science:

• Muscle physiology
• Connective tissue biology
• Developmental biology

Background:

• The diaphragm's interstitial space and collagen content change during postnatal development.
• Understanding these changes is crucial for diaphragm function.

Purpose of the Study:

• To investigate the changes in relative interstitial space and collagen content in the rat diaphragm during postnatal growth.
• To correlate these changes with muscle development and collagen maturation.

Main Methods:

• Computerized image analysis of lectin-stained diaphragm cross-sections to quantify interstitial space.
• High-pressure liquid chromatography (HPLC) to measure hydroxyproline (collagen content) and hydroxylysylpyridinoline (HP, collagen cross-linking).

Main Results:

• Relative interstitial space decreased from ~47% at birth to ~18% in adults.
• Collagen concentration (hydroxyproline) remained constant, but HP levels increased ~17-fold, indicating collagen maturation.
• Reduced interstitial space correlated with increased muscle fiber size.

Conclusions:

• Postnatal diaphragm growth involves a decrease in relative interstitial space, not a change in collagen concentration.
• Increased collagen cross-linking (HP) suggests enhanced collagen density within the developing interstitial space.
• These structural changes may influence the diaphragm's passive mechanical properties.