[Content, location and action site of enkephalins in arterial walls]

Contents of L-enkephalin (L-ENK) and M-enkephalin (M-ENK) in arteries of rabbit were measured by radioimmunoassay. Mean values of L-ENK and M-ENK (pg/mg of wet tissue) were 38.99 +/- 17.29 and 134.67 +/- 8.11 in the rabbit ear artery; 31.10 +/- 7.76 and 93.60 +/- 18.22 in the renal artery; 25.70 +/- 13.60 and 88.43 +/- 18.16 in the mesenteric artery, respectively. L-ENK in these arteries decreased significantly (P less than 0.001) after chemicosympathectomy by injection of 6-OHDA; ENK in the ear artery were reduced significantly (P less than 0.001) following the excision of the superior cervical ganglion or electrical-field stimulation, but not changed after injection of reserpine. Content of NE in the artery strip bath medium was measured by fluorimetric assay. NE in the medium was decreased significantly after administration of L-ENK or M-ENK. The results suggest that enkephalins may exist in the sympathetic nerve terminals innervating arterial walls and may be released by electrical-field stimulation. Enkephalins inhibit the contracting activity of artery strips probably by decreasing the release of NE from sympathetic nerve endings.