Mesenteric lymph flow responses to splanchnic nerve stimulation in sheep

Area of Science:

• Physiology
• Lymphatic System Dynamics
• Autonomic Nervous System

Background:

• The regulation of lymphatic fluid transport is crucial for maintaining tissue fluid balance.
• The role of the autonomic nervous system in modulating lymphatic function requires further elucidation.

Purpose of the Study:

• To investigate the effect of left greater splanchnic nerve stimulation on mesenteric lymph flow in anesthetized sheep.
• To determine the adrenoceptor subtypes involved in mediating these responses.

Main Methods:

• Cannulation of the main mesenteric lymph duct in halothane-anesthetized sheep.
• Continuous recording of lymph flow, lymphatic pressure, and arterial pressure.
• Electrical stimulation of the left greater splanchnic nerve at varying frequencies (1-10 Hz) and assessment of responses before and after phentolamine infusion.

Main Results:

• Splanchnic nerve stimulation significantly increased mesenteric lymph flow in a frequency-dependent manner.
• Lymphatic contraction frequency and mean arterial pressure also increased with stimulation frequency.
• Responses were attenuated by phentolamine, indicating alpha-adrenoceptor mediation.
• Lymph protein concentration remained unchanged, suggesting lymph formation was not the primary driver of increased flow.
• A biphasic lymph flow response was observed: an initial transient increase followed by a decrease.

Conclusions:

• The initial increase in lymph flow is likely mediated by neural stimulation of the lymphatic pump and/or circulating catecholamines.
• The subsequent decrease in lymph flow suggests a reduction in lymph formation during prolonged stimulation.
• Alpha-adrenoceptors play a significant role in mediating the sympathetic nervous system's influence on mesenteric lymph transport.