Pharmacological characterization of CGRP receptors mediating relaxation of the rat pulmonary artery and inhibition of twitch responses of the rat vas deferens

Abstract

1 CGRP receptors mediating vasorelaxation of the rat isolated pulmonary artery and inhibition of contractions of the rat isolated prostatic vas deferens were investigated using CGRP agonists, homologues and the antagonist CGRP . 2 In the pulmonary artery, human (h)a-CGRP-induced relaxation of phenylephrine-evoked tone was abolished either by removal of the endothelium or by N G -nitro-L-arginine (10 75 M). The inhibitory e ect of N G -nitro-L-arginine was stereoselectively reversed by L-but not by D-arginine (10 74 M). Thus, CGRP acts via nitric oxide released from the endothelium. 3 In the endothelium-intact artery, ha-CGRP, hb-CGRP and human adrenomedullin (10 710 ± 3610 77 M), dose-dependently relaxed the phenylephrine-induced tone with similar potency. Compared with ha-CGRP, rat amylin was around 50 fold less potent, while [Cys(ACM 2,7 )] ha-CGRP (10 77 ± 10 74 M) was at least 3000 fold less potent. Salmon calcitonin was inactive (up to 10 74 M). 4 Human a-CGRP 8-37 (3610 77 ± 3610 76 M) antagonized ha-CGRP (pA 2 6.9, Schild plot slope 1.2+0.1) and hb-CGRP (apparent pK B of 7.1+0.1 for ha-CGRP 8-37 10 76 M) in the pulmonary artery. Human b-CGRP 8-37 (10 76 M) antagonized ha-CGRP responses with a similar a nity (apparent pK B 7.1+0.1). Human adrenomedullin responses were not inhibited by ha-CGRP 8-37 (10 76 M). 5 In the prostatic vas deferens, ha-CGRP, hb-CGRP and rat b-CGRP (10 710 ± 3610 77 M) concentration-dependently inhibited twitch responses with about equal potency, while rat amylin (10 78 ± 10 75 M) was around 10 fold less potent and the linear analogue [Cys(ACM 2,7 )] ha-CGRP was at least 3000 fold weaker. Salmon calcitonin was inactive (up to 10 74 M). 6 The antagonist e ect of ha-CGRP 8-37 (10 75 ± 3610 75 ) in the vas deferens was independent of the agonist, with pA 2 values against ha-CGRP of 6.0 (slope 0.9+0.1), against hb-CGRP of 5.8 (slope 1.1+0.1), and an apparent pK B value of 5.8+0.1 against both rat b-CGRP and rat amylin. Human b-CGRP 8-37 (3610 75 ± 10 74 M) competitively antagonized ha-CGRP responses (pA 2 5.6, slope 1.1+0.2).The inhibitory e ect of ha-CGRP on noradrenaline-induced contractions in both the prostatic and epididymal vas deferens was antagonized by ha-CGRP 8-37 (pA 2 5.8 and 5.8, slope 1.0+0.2 and 1.0+0.3, respectively). 7 The e ects of ha-CGRP and ha-CGRP 8-37 in both rat pulmonary artery and vas deferens were not signi®cantly altered by pretreatment with peptidase inhibitors (amastatin, bestatin, captopril, phosphoramidon and thiorphan, all at 10 76 M). The weak agonist activity of [Cys(ACM 2,7 )] ha-CGRP in the vas deferens was not increased by peptidase inhibitors. 8 These data demonstrate that two di erent CGRP receptors may exist in the rat pulmonary artery and vas deferens, a CGRP 1 receptor subtype in the rat pulmonary artery (CGRP 8-37 pA 2 6.9), while the lower a nity for CGRP 8-37 (pA 2 6.0) in the vas deferens is consistent with a CGRP 2 receptor.

Endogenous CGRP protects against neointimal hyperplasia following wire-induced vascular injury

“…In rat aorta [44] and pulmonary artery [45], CGRP interacts with endothelial receptors, stimulating the release of endothelium-derived relaxing factors. By contrast, in cat cerebral [46], pig coronary [47] and rat mesenteric vessels [48], CGRP acts directly on VSMCs.…”

cAMP Signal Transduction Cascade, a Novel Pathway for the Regulation of Endothelial Nitric Oxide Production in Coronary Blood Vessels

“…CGRP, a vasodilator neuropeptide, is widely distributed in the autonomic nerve terminals supplying the cardiovascular system and is present in plasma. 24,45,46 Recent studies 24,45,[47][48][49] have found that CGRP can also evoke endothelium-dependent and NO-mediated vasodilation. Adrenomedullin shares significant structural homology with CGRP.…”

CGRP and migraine: neurogenic inflammation revisited

“…Exceptions to endothelium-independent relaxation to CGRP occur only in a few tissues, including the rat aorta, where the relaxation to CGRP depends on the presence of an intact endothelium and is attenuated by inhibitors of NO synthase, implying an NO-dependent mechanism [12,50]. In human internal mammary artery [51] and rat pulmonary artery [52], a similar endothelium-dependent mechanism of relaxation has also been seen. Evidence that CGRP activates phospholipase C in HEK293 cells, lead-ing to an increase in intracellular Ca 2+ via inositol trisphosphate (IP3) [53] suggests that this alternative intracellular pathway may be responsible for the CGRP-induced release of NO (Fig.…”