Mesenteric lymph flow in adult and aged rats

Area of Science:

• Physiology
• Aging Research
• Vascular Biology

Background:

• Aging is associated with altered vascular function.
• Mesenteric lymphatic vessels (MLVs) are crucial for fluid homeostasis and immune surveillance.
• Age-related changes in lymphatic function can impact tissue fluid balance.

Purpose of the Study:

• To investigate aging-associated changes in mesenteric lymphatic vessel (MLV) contractile characteristics and lymph flow in vivo.
• To assess the role of nitric oxide (NO) in regulating aged MLV function.
• To compare ex vivo and in vivo lymphatic vessel contractile properties.

Main Methods:

• In vivo assessment of MLV diameter, contraction amplitude, and frequency in young (9-month-old) and aged (24-month-old) male Fischer-344 rats.
• Measurement of lymph flow velocity, wall shear stress, and minute active wall shear stress load before and after N(ω)-nitro-L-arginine methyl ester hydrochloride (L-NAME) administration.
• Comparative analysis of in vivo and ex vivo isolated lymphatic vessel contractile characteristics.

Main Results:

• Aged MLVs exhibited severely depleted active pumping, primarily due to a reduced contraction frequency.
• Age-related MLV enlargement correlated with a lower minute active shear stress load compared to adult vessels.
• Nitric oxide (NO) elimination via L-NAME administration rapidly restored aged MLV pumping to adult levels by increasing contraction frequency.
• Ex vivo isolated lymphatic vessels demonstrated contractile characteristics identical to those in vivo.

Conclusions:

• Aging significantly impairs mesenteric lymphatic vessel (MLV) pumping capacity, mainly through decreased contraction frequency.
• Nitric oxide (NO) plays a critical role in modulating aged MLV function, potentially counterbalancing stimulatory metabolites in surrounding tissues.
• Restoration of MLV function in aged rats is achievable through NO inhibition, highlighting a potential therapeutic target.