Absence of restricted diffusion in adipose tissue capillaries

Area of Science:

• Physiology
• Biophysics
• Vascular Biology

Background:

• Understanding capillary permeability is crucial for drug delivery and understanding tissue function.
• Previous studies utilized 51Cr-EDTA, but its diffusion characteristics in adipose tissue require further clarification.
• Adipose tissue's unique metabolic role necessitates specific investigation into its microvascular properties.

Purpose of the Study:

• To quantify capillary permeability in adipose tissue using 57Co-cyanocobalamin (57Co-B12).
• To compare the diffusion of 57Co-B12 with 51Cr-EDTA in adipose tissue.
• To evaluate existing models of capillary pore size and structure based on experimental findings.

Main Methods:

• Employed the single injection, external registration method to measure capillary diffusion capacity (CDC).
• Calculated the permeability-surface area product (PS), capillary extraction, and plasma flow for 57Co-B12.
• Compared experimental data with previously obtained 51Cr-EDTA data using similar methodologies.

Main Results:

• The capillary diffusion capacity (CDC) for 57Co-B12 was determined to be 1.1 ml/100 g-min.
• The ratio of diffusion coefficients (51Cr-EDTA/57Co-B12) was 1.79, closely matching the ratio of CDC values (1.81).
• Established models for pore radius and slit width were insufficient to explain the observed diffusion rates.

Conclusions:

• Concluded that 57Co-B12 diffusion in adipose tissue is not restricted compared to 51Cr-EDTA.
• Suggested that the transendothelial channel system of fused vesicles may explain the observed permeation.
• Supported the hypothesis that continuous capillaries exhibit consistent permeation characteristics across different tissues.