Abstract
The effect of long-term guanethidine sympathectomy and short-term 6-hydroxydopamine (6-OHDA) sympathectomy on the release of endothelial vasoactive substances by high flow from the rat mesenteric arterial bed was examined. Preparations were perfused at a constant flow rate of 5 ml/min with Krebs' solution, and at 25 ml/min for 2 min. During increased flow there was a release of adenosine 5′-triphosphate (ATP), endothelin, vasopressin and substance P into the perfusate. In preparations from guanethidine-treated rats the flow-evoked release of endothelin (median: 23.55 pmol/min) was significantly greater than that in the controls (median: 0.37 pmol/min) (P < 0.05). Flow-evoked release of ATP, vasopressin and substance P was similar between the groups. After short-term sympathectomy with 6-OHDA an increase in flow was accompanied by the release of ATP, endothelin, vasopressin and substance P which was not significantly different between control and 6-OHDA treated preparations. These results show that after long-term sympathectomy there is an increase in the flow-evoked release of endothelin from the rat mesenteric arterial bed which does not occur after short-term sympathectomy. It is suggested that sympathetic nerves may have long-term trophic effects on the content of endothelial vasoactive substances which may be expressed as a selective alteration in their patterns of release after stimuli such as increased flow.