The Effect of in Vivo and in Vitro Capsaicin Treatment on Endothelium Dependent Relaxation

Abstract

The ability of vasoactive agents to induce endothelium-dependent vascular relaxation appears to depend on a number of factors. We have examined the contribution of specific peptidergic perivascular nerve fibers to endothelium dependent vascular relaxation elicited by acetylcholine. Adult rats were treated with capsaicin (50mg/kg on two consecutive days) under ether anesthesia. An equal number of rats was treated in the same way with capsaicin vehicle (10% Tween 80, 10% ethanol in normal saline). One week after treatment of adult rats, treated and age-matched untreated rats were anesthetized (sodium pentobarbitone, 35mg/kg i.p.) and the superior mesenteric arterial bed removed. The superior mesenteric artery was cannulated and perfused at a constant rate of flow (3ml/min) with Krebs’ solution. Methoxamine (0.4–1 ×10-5M, gift from Burroughs Wellcome) was added to the perfusing solution to produce a constriction of the arterial bed sufficient to raise the pressure above 100mmHg. Capsaicin (10-5M), acetylcholine (10-8M, 5 × 10-7M), A23187 (10-8M, 5 × 10-8M) and sodium nitroprusside (10-4M) were tested for their ability to produce relaxation. Following application of acetylcholine or A23187, 1-arginine (10-4M) was added to the perfusing solution once a stable pressure had been achieved. This protocol was also carried out on vessel beds from treated and untreated rats following perfusion for ten minutes with Krebs’ solution containing capsaicin (10-5M). At the conclusion of each experiment, the vessel beds were processed for immunohistochemical demonstration of substance P and calcitonin gene-related peptide immunoreactive perivascular innervation.