Structure-Activity Study of Chicken Calcitonin Gene-Related Peptide (CGRP) on Vasorelaxation in Rat Mesenteric Resistance Vessels.

1 Intracellular recording was used to investigate the electrophysiological effects of activating peptidergic primary afferent axons with capsaicin in the smooth muscle of rat mesenteric arteries in vitro. In addition, continuous amperometry was used to monitor the effects of capsaicin on noradrenaline release from the sympathetic nerves. 2 Capsaicin (1 mm) produced a hyperpolarization (À1172 mV) and a reduction in the time constant of decay of excitatory junction potentials (e.j.p.'s) evoked by electrical stimulation of the perivascular sympathetic nerves. These effects of capsaicin were mimicked by calcitonin gene-related peptide (CGRP; 1 and 10 nm) but not by substance P (50 nm), which produced a small hyperpolarization (maximum À371 mV) but did not change excitatory junction potential (e.j.p.) time course. 3 The hyperpolarization produced by capsaicin and CGRP was blocked by glibenclamide (10 mm) but was not changed by the CGRP antagonist, CGRP 8 -37 (0.5 mm). Mechanical denudation of the endothelium also did not reduce the effect of capsaicin on membrane potential. 4 Capsaicin (1 mm) increased the amplitude of e.j.p.'s. This effect was not mimicked by CGRP or substance P nor blocked by glibenclamide or CGRP 8 -37 . 5 All effects of capsaicin desensitized. 6 Capsaicin (1 mm) had no effect on noradrenaline-induced oxidation currents evoked by electrical stimulation, indicating that noradrenaline release was unchanged. 7 These results suggest that CGRP released from primary afferent axons hyperpolarizes vascular smooth muscle by activating glibenclamide-sensitive K þ channels. The findings also indicate that an unknown factor released by the primary afferent axons increases e.j.p. amplitude.

Section: Discussionsupporting

confidence: 53%

Section: Discussionmentioning

confidence: 99%

Electrophysiological effects of activating the peptidergic primary afferent innervation of rat mesenteric arteries

Dunn

Hardy

Brock

2003

“…It is noteworthy that for hα CGRP 8–37 , both vasodilator and vasoconstrictor effects have been reported. For instance, a vasodilator component was noted in rabbit skin, in vivo (Hughes & Brain, 1991) and cat cerebral vasculature (Wahl et al ., 1994), while vasoconstriction was observed in rat perfused mesenteric artery (Han et al ., 1990; Nuki et al ., 1994b), perfused kidney (Chin et al ., 1994) and the rat vasculature, in vivo (Gardiner et al ., 1990). Therefore, the present findings illustrate that not only hα CGRP 8–37 but also its analogues have limitations as antagonists, underlining the need for more selective compounds.…”

Section: Discussionmentioning

confidence: 99%

Bioactive β‐bend structures for the antagonist hα CGRP_8–37 at the CGRP₁ receptor of the rat pulmonary artery

Wisskirchen¹,

Doyle²,

Gough³

et al. 2000

The aim of this study was to determine β‐bend structures and the role of the N‐ and C‐terminus in the antagonist hα CGRP8–37 at the rat pulmonary artery CGRP receptor mediating hα CGRP relaxation. Hα CGRP8–37 Pro16 (10−6 M), with a bend‐biasing residue (proline) at position 16, did not antagonize hα CGRP responses, while a structure‐conserving amino acid (alanine16) at the same position retained antagonist activity (apparent pKB 6.6±0.1; 10−6 M). Hα CGRP8–37 Pro19 (10−6 M), with proline at position 19 was an antagonist (apparent pKB 6.9±0.1). Incorporation of a β‐bend forcing residue, BTD (beta‐turn dipeptide), at positions 19 and 20 in hα CGRP8–37 (10−6 M) antagonized hα CGRP responses (apparent pKB 7.2±0.2); and BTD at positions 19,20 and 33,34 within hα CGRP8–37 was a competitive antagonist (pA2 7.2; Schild plot slope 1.0±0.1). Hα CGRP8–37 analogues, substituted at the N‐terminus by either glycine8 or des‐NH2 valine8 or proline8 were all antagonists (apparent pKB 6.9±0.1; (10−6 M), 7.0±0.1 (10−6 M), and pA2 7.0 (slope 1.0±0.2), respectively); while replacements by proline8 together with glutamic acid10,14 in hα CGRP8–37 (10−6 M) or alanine amide37 at the C‐terminus of hα CGRP8–37 (10−5 M) were both inactive compounds. In conclusion, possible bioactive structures of hα CGRP8–37 include two β‐bends (at 18–21 and 32–35), which were mimicked by BTD incorporation. Within hα CGRP8–37, the N‐terminus is not essential for antagonism while the C‐terminus may interact directly with CGRP1 receptors in the rat pulmonary artery. British Journal of Pharmacology (2000) 129, 1049–1055; doi:

“…Another study showed that human-aCGRP(8 ± 37) has competitive antagonistic activity in pig coronary arteries with a pK B value of 6.7 (Gray et al, 1991). In rat mesenteric small artery, the pK B value falls within the range 7.2 to 7.6 Lei et al, 1994;Nuki et al, 1994). In rat thoracic aorta, human-aCGRP(8 ± 37) seems to be a non-competitive antagonist of human-aCGRP (Gray et al, 1991) adding to the complexity of CGRP-receptor characterization.…”

Section: Discussionmentioning

confidence: 99%

Characterization of calcitonin gene‐related peptide(CGRP) receptors in intramural coronary arteries from male and female Sprague Dawley rats

Sheykhzade

Nyborg

1998

1 In this study we characterized the CGRP-receptor subtype by Schild-plot analysis using the Cterminal fragment, human-aCGRP(8 ± 37), a putative competitive CGRP 1 -receptor selective antagonist. In addition, the e ect of rat-aCGRP was compared with that of homologous peptides rat-bCGRP, ratamylin, rat-adrenomedullin and [Cys(Acm) 2,7 ]-human-aCGRP, a putative selective CGRP 2 -receptor agonist, in the left coronary arteries of 3 months old male and female Sprague Dawley rats. 2 Isolated rings from the distal, intramural part of the left anterior descending (LAD) coronary artery in both groups of rats were mounted on a double wire-myograph. The arteries were then stretched to their optimal lumen diameter for active tension development and precontracted with 10 75 M prostaglandin F 2a (PGF 2a ), after which agonists were added to the organ bath in a cumulative manner. 3 Rat-aCGRP induced endothelium-independent relaxations in male and female Sprague-Dawley rats. Rat-bCGRP concentration-response relations (10 711 ± 10 77 M) were similar to those of rat-aCGRP in either sex. The maximal relaxations induced by rat-amylin and rat-adrenomedullin, both at 10 76 M, were signi®cantly (P50.05) lower than those induced by rat-a-and rat-bCGRP. In contrast, the selective CGRP 2 -receptor agonist [Cys(Acm) 2,7 ]-human-aCGRP failed to induce signi®cant relaxations at the highest concentration used (10 77 M) in the coronary arteries of male and female rats. 5 The C-terminal fragment, human-aCGRP(8 ± 37) blocked concentration-dependently (10 77 ± 10 76 M) the rat-aCGRP-induced relaxation in 10 75 M PGF 2a -precontracted coronary arteries. The slopes of the regression lines of the Schild-plots for both male and female rats were not signi®cantly (P40.05) di erent from unity and the pA 2 values for human-aCGRP(8 ± 37) were 6.93 and 6.98 in arteries from male and female rats, respectively. There was no signi®cant (P40.05) di erence in estimated pK B values for human-aCGRP(8 ± 37) between male (6.99+0.10, n=13) and female (6.95+0.08, n=13) rats. 6 The concentration-response relationships for rat-a-and rat-bCGRP were similar in male and female Sprague Dawley rats. The predominant CGRP receptor subtype in small intramural coronary arteries appeared to belong to the CGRP 1 -receptor subtype in both sexes.