Resistance in the sheep's lymphatic system.

Area of Science:

• Physiology
• Lymphatic System Dynamics

Background:

• The lymphatic system is crucial for fluid homeostasis and immune function.
• Understanding peripheral lymphatic resistance is vital for managing lymphedema and related conditions.

Purpose of the Study:

• To quantify the resistance of the peripheral lymphatic system in sheep.
• To determine the intralymphatic pressures required to achieve physiological lymph flow rates.

Main Methods:

• Saline infusion into afferent lymphatics of anesthetized sheep's metacarpal region.
• Measurement of inflow pressure across a range of flow rates (10-2000 µL/min).
• Assessment of isoprenaline's effect on lymphatic resistance and contractility.

Main Results:

• Physiological flow rates generated mean pressures of approximately 30 mmHg.
• Lymphatic resistance was high at low flow rates (<15 µL/min) but decreased significantly at higher flows (>500 µL/min).
• Isoprenaline reduced spontaneous contractions and lowered resistance at lower flow rates.

Conclusions:

• The sheep peripheral lymphatic system exhibits substantial resistance to lymph flow.
• Significant intralymphatic pressure is necessary for peripheral lymph return, especially under high flow conditions.