Peptidergic nerve involvement in the control of endothelium-dependent vascular relaxation

The ability of Acetylcholine (ACh) and A23187 to induce endothelium-dependent relaxation was compared in the isolated perfused mesenteric arterial bed of untreated adult rats, adult rats treated neonatally with capsaicin, and adult rats treated as adults with capsaicin. Following neonatal capsaicin treatment, the response to both agents was reduced. Following adult treatment, the response to both agents was reduced seven days following capsaicin treatment. The same results were obtained in the presence of L-arginine or indomethacin. Tissues from all rats responded equally to sodium nitroprusside. Following capsaicin treatment no change in the structural relationship of the arterial intima was detected but no perivascular nerve fibres immunoreactive to substance P (SP) or calcitonin gene-related peptide (CGRP) could be demonstrated. It is suggested that the reduced response to ACh and A23187 does not involve a change in endothelial muscarinic receptors or a structural change in the arterial intima, but is directly related to the absence of immunohistochemically demonstrable CGRP/SP-containing perivascular innervation.