Enhanced fluid uptake in frog mesenteric capillaries associated with plasmin perfusion

Area of Science:

• Physiology
• Biochemistry
• Microcirculation Research

Background:

• Capillary permeability is crucial for fluid exchange and tissue homeostasis.
• The fibrinolytic enzyme plasmin plays a role in regulating blood clot breakdown.
• Understanding plasmin's direct effects on capillary wall properties is essential.

Purpose of the Study:

• To investigate the impact of plasmin perfusion on single frog mesenteric capillary permeability.
• To measure changes in hydraulic permeability (Lp) and effective oncotic pressure (sigma delta pi) during plasmin exposure.
• To explore the influence of temperature on plasmin's effects on capillary fluid filtration.

Main Methods:

• Single frog mesenteric capillaries were perfused with Ringer solutions containing Ficoll 70 and/or bovine serum albumin (BSA).
• Hydraulic permeability (Lp) and effective oncotic pressure (sigma delta pi) were measured using the Michel method (1980).
• Capillaries were subsequently perfused with solutions containing plasmin (1 mg/ml) to assess its effects, with temperature variations.

Main Results:

• Plasmin perfusion significantly increased effective oncotic pressure (sigma delta pi) in 16 out of 17 experiments.
• Hydraulic permeability (Lp) showed a non-significant decrease during plasmin perfusion.
• Plasmin's effects on reducing fluid filtration or increasing reabsorption were more pronounced at 17°C compared to 4°C.

Conclusions:

• Plasmin significantly alters capillary wall properties, primarily by increasing oncotic pressure, possibly via endothelial cell surface interactions.
• The observed increase in oncotic pressure suggests local osmotic gradients are generated by plasmin's action.
• Temperature modulates plasmin's effects on capillary fluid dynamics, with greater impact at physiological temperatures.