Anandamide-induced depressor effect in spontaneously hypertensive rats - Role of the vanilloid receptor

To test the hypothesis that activation of the vanilloid receptor (VR1) contributes to the anandamide-induced depressor effect in spontaneously hypertensive rats (SHR), we used a selective VR1 antagonist capsazepine (CAPZ) and a selective cannabinoid type 1 receptor antagonist SR141716A in conjunction with a VR1 agonist capsaicin in both SHR and Wistar-Kyoto rats (WKY). Mean arterial pressure was increased in SHR compared with WKY (P<0.05). Intravenous administration of capsaicin caused a greater depressor response in SHR compared with WKY (P<0.05), which was blocked by approximate to60% by CAPZ (P<0.05) in SHR only. Methanandamide caused a similar greater depressor response (P<0.05), which was blocked by approximate to50% and 60% by CAPZ and SR141716A, respectively, in SHR (P<0.05) but not in WKY. Radioimmunoassay showed that methanandamide increased plasma calcitonin gene-related peptide (CGRP) levels from baseline in both SHR and WKY (P<0.05), with no difference between 2 strains. Western blot showed that protein expression for the calcitonin receptor-like receptor-but not receptor activity modifying protein 1, VR1, and cannabinoid type 1 receptors-was increased in mesenteric resistance arteries in SHR compared with WKY (P<0.05). These data indicate that in addition to activation of cannabinoid type 1, anandamide may serve as an endogenous compound to stimulate VR1, leading to a decrease in blood pressure via CGRP release from sensory nerve terminals. Increased mesenteric CGRP receptor expression in SHR may account for increased sensitivity of blood pressure to anandamide and may serve as a compensatory response to buffer the increase in blood pressure in SHR.