Article date: May 2000
By: F M Wisskirchen, I Marshall in Volume 130, Issue 2, pages 464-470
The CGRP receptor mediating relaxation of the rat internal anal sphincter (IAS) has been characterized using CGRP analogues, homologues, the antagonist CGRP8–37 and its analogues.
In isolated IAS strips, the spontaneously developed tone was concentration‐dependently relaxed by hα CGRP, hβ CGRP and rat β CGRP (pEC50 8.1±0.2, 8.3±0.1 and 8.4±0.2, respectively; 100% maximum response). Vasoactive intestinal polypeptide (VIP) was around 7 fold more potent than hα CGRP (pEC50 9.0±0.1; 100% maximum relaxation). [Cys(ACM2.7)] hα CGRP and salmon calcitonin were inactive (up to 10−5 M).
Hα CGRP8–37 (10−5 M) antagonized responses to hα CGRP (apparent pKB 5.7±0.3) and rat β CGRP (apparent pKB 5.8±0.2), but not to VIP. Hβ CGRP8–37 (10−5 M) was an antagonist against hα CGRP (apparent pKB 6.1±0.1). Hα CGRP8–37 analogues (10−5 M), with substitutions at the N‐terminus by either glycine8 or des‐NH2 valine8 or proline8, antagonized hα CGRP responses with similar affinities (apparent pKB 5.8±0.1, 5.8±0.1 and 5.5±0.1, respectively).
Peptidase inhibitors (amastatin, bestatin, captopril, phosphoramidon and thiorphan, 10−6 M each) did not increase the agonist potency of either hα CGRP or [Cys(ACM2,7)] hα CGRP, or the antagonist affinity of hα CGRP8–37 against hα CGRP or rat β CGRP.
These data demonstrate for the first time a CGRP receptor in the rat IAS for which hα CGRP 8–37 and its analogues have an affinity that is consistent with a CGRP2 receptor. However, there is a marked species difference as the antagonist has a 100 fold lower affinity in the rat than in the same tissue of the opossum (Chakder & Rattan, 1991).
The CGRP receptor mediating relaxation of the rat internal anal sphincter (IAS) has been characterized using CGRP analogues, homologues, the antagonist CGRP8–37 and its analogues.
In isolated IAS strips, the spontaneously developed tone was concentration‐dependently relaxed by hα CGRP, hβ CGRP and rat β CGRP (pEC50 8.1±0.2, 8.3±0.1 and 8.4±0.2, respectively; 100% maximum response). Vasoactive intestinal polypeptide (VIP) was around 7 fold more potent than hα CGRP (pEC50 9.0±0.1; 100% maximum relaxation). [Cys(ACM2.7)] hα CGRP and salmon calcitonin were inactive (up to 10−5 M).
Hα CGRP8–37 (10−5 M) antagonized responses to hα CGRP (apparent pKB 5.7±0.3) and rat β CGRP (apparent pKB 5.8±0.2), but not to VIP. Hβ CGRP8–37 (10−5 M) was an antagonist against hα CGRP (apparent pKB 6.1±0.1). Hα CGRP8–37 analogues (10−5 M), with substitutions at the N‐terminus by either glycine8 or des‐NH2 valine8 or proline8, antagonized hα CGRP responses with similar affinities (apparent pKB 5.8±0.1, 5.8±0.1 and 5.5±0.1, respectively).
Peptidase inhibitors (amastatin, bestatin, captopril, phosphoramidon and thiorphan, 10−6 M each) did not increase the agonist potency of either hα CGRP or [Cys(ACM2,7)] hα CGRP, or the antagonist affinity of hα CGRP8–37 against hα CGRP or rat β CGRP.
These data demonstrate for the first time a CGRP receptor in the rat IAS for which hα CGRP 8–37 and its analogues have an affinity that is consistent with a CGRP2 receptor. However, there is a marked species difference as the antagonist has a 100 fold lower affinity in the rat than in the same tissue of the opossum (Chakder & Rattan, 1991).
British Journal of Pharmacology (2000) 130, 464–470; doi:10.1038/sj.bjp.0703315
DOI: 10.1038/sj.bjp.0703315
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