MEDIATION OF EXCITATORY NEUROTRANSMISSION BY THE RELEASE OF ATP AND NORADRENALINE IN SHEEP MESENTERIC LYMPHATIC VESSELS

1. Spontaneous isometric contractions were measured in rings of sheep mesenteric lymphatics. Field stimulation at short pulse widths increas ed the frequency of spontaneous contractions and this response was blo cked by 3 x 10(-7) M omega-conotoxin and by 10(-6) M guanethidine. 2. Rings that had been incubated with [H-3]noradrenaline released H-3 in response to field stimulation in a frequency-dependent manner. 3. Exog enous ATP mimicked the response to field stimulation and this was bloc ked by 10(-4) M suramin but not by prior desensitization with 10(-6) M alpha,beta-methylene ATP. Exogenous noradrenaline was not blocked by 10(-4) M suramin.4. The excitatory response to field stimulation was n ot blocked by 10(-4) M suramin but a combination of 10(-4) M suramin a nd 3 x 10(-6) M phentolamine did block the response. 5. In rings taken from sheep that had been pretreated with reserpine, 10(-4) M suramin alone blocked the response to field stimulation. 6. The results of thi s study suggest that the excitatory response to stimulation of intramu ral nerves in sheep mesenteric lymphatics is mediated by the release o f both ATP and noradrenaline.