Sampling interstitial fluid from rat skeletal muscles by intermuscular wicks

Area of Science:

• Physiology
• Biochemistry
• Biomaterials

Background:

• Accurate sampling of interstitial fluid is crucial for understanding tissue physiology.
• Existing methods may introduce artifacts due to inflammation or cellular damage.
• The implanted wick technique offers a potential solution for in vivo and postmortem fluid collection.

Purpose of the Study:

• To adapt and validate a modified implanted wick method for sampling interstitial fluid from rat skeletal muscles.
• To assess the quality and composition of interstitial fluid collected using this modified technique.
• To compare fluid composition obtained postmortem versus in vivo.

Main Methods:

• A modified dry nylon wick insertion technique into intermuscular spaces of rat hindlimbs.
• Postmortem wick insertion to prevent inflammatory protein extravasation and muscle cell contamination.
• Analysis of wick fluid protein and albumin concentrations via electrophoresis and isotope studies.
• Comparison of postmortem wick fluid with in vivo implanted wick fluid.

Main Results:

• Postmortem intermuscular wicks yielded fluid with protein concentrations (24.1-28.5 mg/ml) and albumin levels (13.0-13.9 mg/ml) lower than plasma.
• Electrophoresis showed a plasma-like protein profile, with no detected muscle cell proteins.
• Isotope studies confirmed minimal direct plasma albumin (<2%) and no postmortem concentration by cell swelling.
• In vivo wicks showed similar total protein but lower albumin-to-globulin ratios and significant albumin leakage from plasma (approx. 50%).

Conclusions:

• The modified postmortem wick method effectively samples rat muscle interstitial fluid, minimizing contamination from inflammation and cellular damage.
• This technique provides a reliable method for studying muscle interstitial fluid composition.
• The in vivo method requires careful consideration of protein leakage from plasma due to implantation trauma.