Transient Excitatory Responses to Sustained Stimulation of Intramural Nerves in Isolated Bovine Lymphatic Vessels

Abstract

SUMMARYSpontaneous isometric contractions were measured in 2 cm segments of bovine mesenteric lymphatics. Field stimulation at 4 Hz was applied for a 20 min period. This caused a threefold increase in contraction frequency initially but the response faded rapidly so that, within 6 min of the beginning of stimulation, contraction frequency had returned to a value which was not significantly different from control. In contrast to the effect on frequency 3H efflux from vessels pre-loaded with [3H]noradrenaline was maintained at a value significantly higher than control for the entire stimulation period. The fade in response to exogenous noradrenaline was similar to that seen with field stimulation but with a slightly slower time course. Vessels desensitized with noradrenaline showed a greatly diminished response to field stimulation but responded normally to other agonists. Increasing the extracellular KCI concentration to 18 mm also caused a threefold increase in contraction frequency but, unlike the response to noradrenaline and field stimulation, this was maintained for the 20 min period during which [K+]. was raised.The results suggest that the adrenoceptors on lymphatic smooth muscle exhibit very rapid homologous desensitization.

Release of [3H]‐noradrenaline from the sympathetic nerves to bovine mesenteric lymphatic vessels and its modification by α‐agonists and antagonists

“…Figure 11 summarizes the results from 5 experiments in which 3H release to 1 and 4 Hz stimulation was examined before and after the addi- with an approximately four fold increase in contraction frequency, although this was not maintained in the continued presence of the drug. Relatively rapid postsynaptic desensitization to noradrenaline is a characteristic of these vessels and has been described previously (McHale et al, 1988). In the presence of the drug, evoked 3H efflux (P < 0.05) was significantly decreased at both frequencies and the postsynaptic response was obviously reduced at 1 Hz.…”

Imaging the lymphatic system

“…When more control over experimental conditions is desired, lymphatic vessels can be isolated and cannulated ex vivo in order to study the effects of pressure, flow, electrical stimulation or biochemical agents on the contractile behavior (Davis et al, 2008; Davis et al, 2012; Fox and von der Weid, 2002; Gashev et al, 2009; McHale and Roddie, 1976; McHale et al, 1988; Scallan et al, 2013; Zawieja et al, 2012). In general, images are acquired of the isolated vessel at 24 frames per second or faster, and parameters such as minimum and maximum diameters, contraction amplitude, contraction frequency and ejection fraction are measured by image analysis.…”