Comparative Characterization of Capsule Mechanical Properties in Mesenteric Lymph Nodes of Young and Aging Bulls

The efficiency of the lymph transport system affects not only the balance of the interstitial fluid, but also other aspects of homeostasis. Lymph transport from the interstitial space to the main veins is mainly provided by rhythmic contractions of the lymphatic vascular segments, lymphangions. Meanwhile, the lymphatic vascular network sequentially incorporates the lymph nodes whose role in lymph transport is poorly understood. The aims of this work were to study the length–tension ratio in the bull mesenteric lymph node capsule and to calculate the pressure the lymph nodes are able to generate, as well as to compare the active and passive mechanical characteristics of the lymph node capsule in young and aging bulls. Experiments on isolated lymph node capsules have shown that lymph nodes are highly extensible structures, which allows them to fill readily with lymph even at the peak of lymph formation. Our data show that the bull mesenteric lymph nodes share the ability to regulate lymph flow along them via the intrinsic mechanisms. Smooth muscle cells in the lymph node capsule are sensitive to stretching, as manifested in an increase in the strength of contractions with an increase in capsule stretching. Lymph nodes are able to generate high active pressure with a significant increase in volume and passive pressure. The extensibility of the lymph node capsule and the active pressure developed by the nodes during spontaneous contractions decline in aging vs. young bulls. Thus, we provide here the first measurements and analysis of the capsular length–tension and nodular diameter–pressure ratios in the mesenteric lymph nodes of young and aging bulls.