Differential effects of anaesthesia on the contractility of lymphatic vessels in vivo.

KEY POINTS: Contractility of lymphatic collectors is essential for the functionality of the lymphatic system and, thus, for lymph flow. Previously published rates of lymphatic collectors in mice vary from 1.1 to 17 contractions/min with little agreement between investigators. In this study, we focused on the effects of different anaesthesia regimens on lymphatic vessel contractility using in vivo imaging approaches. We show that isoflurane and pentobarbital have an inhibitory effect on lymphatic contractility compared to mice under other anaesthesia regimens and in awake conditions. These results should help to establish a standardization of lymphatic contraction studies in mice and may also have relevance for patients undergoing anaesthesia during surgery. ABSTRACT: Contractions of collecting lymphatic vessels are essential for the function of the lymphatic vascular system, due to the lack of a central pump to drive flow. A wide range of physiological contraction frequencies and strengths have been reported in previous in vivo studies in mice. This is probably due to the different types of anaesthesia that have been used and which might have exerted direct influences on lymphatic vessel function. We investigated six commonly used anaesthesia regimens for their influence on lymphatic vessel contractility using near-infrared in vivo imaging approaches. Non-invasive imaging of the lymphatic leg collector revealed distinct effects of the anaesthesia regimens with reduced contraction activity under isoflurane and pentobarbital anaesthesia. Isoflurane also reduced the contractility of near-infrared dye-loaded vessels during invasive imaging of the lymphatic flank collector whereas the combination of ketamine/xylazine/acepromazine had no major effects. The transport time of a lymphatic-specific dye from the skin through the lymphatic vasculature to the systemic bloodstream was also delayed under isoflurane anaesthesia. Based on these results, we recommend use of combinations of ketamine and medetomidine for future non-invasive studies and of ketamine, xylazine and acepromazine for invasive studies. Beyond their importance for facilitating the interpretation and planning of animal studies, our findings might also have relevance for human patients undergoing anaesthesia for surgical procedures.