Supersensitivity in rat micro‐arteries after short‐term denervation

Contractile responses to phenylephrine and high‐K+ were investigated in vitro in microvascular preparations from the rat medial plantar artery, a branch from the saphenous artery, obtained after short‐term denervation in vivo. Two groups of animals were studied: (1) animals undergoing surgical resection of the saphenous nerve, and (2) animals undergoing surgical resection of both the sciatic and saphenous nerves. The animals were operated on one side only. Microvascular preparations (diameter about 325 μm) were obtained 10 days after surgery. Vessels from the non‐operated side served as controls. Immunocytochemistry showed a decreased number of both neuropeptide Y (NPY) and calcitonin gene‐related peptide (CGRP) immunoreactive nerve fibres in vessels after resection of the saphenous nerve only. Resection of both the saphenous and the sciatic nerve caused a complete loss of immunoreactive nerve fibres. Mechanical measurements were performed using a wire myograph. In vessels subjected to resection of the saphenous nerve the sensitivity to phenylephrine was similar to controls. Vessels denervated by resection of both the saphenous and sciatic nerves showed significant increases in phenylephrine and potassium sensitivity. When depolarized in high‐K+ solution the denervated vessels showed an increased sensitivity to extracellular Ca2+. The results show that complete short‐term denervation of the rat medial plantar artery in vivo causes a pronounced supersensitivity in the vascular smooth muscle. The supersensitivity appears not to be restricted to the sympathetic α‐receptors but also associated with changes in the cellular excitation‐contraction coupling. Such altered reactivity of the vascular smooth muscle may contribute to vascular disturbances observed in vivo after nerve damage or surgical denervation.