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Characterization of the relaxant action of urocortin, a new peptide related to corticotropin‐releasing factor in the rat isolated basilar artery

1998; Wiley; Volume: 125; Issue: 6 Linguagem: Inglês

10.1038/sj.bjp.0702182

1476-5381

Lothar Schilling, Ch Kanzler, Peter Schmiedek, Hannelore Ehrenreich,

Neuroendocrine regulation and behavior

In addition to its well established neuroendocrine and neurotransmitter effects, corticotropin releasing factor (CRF) exerts a potent vasorelaxant action. Recently, a CRF‐related peptide, urocortin, has been identified in the mammalian brain. In the present study, the cerebral vasomotor action of this peptide and the mechanism underlying its relaxant effect are characterized. Ring segments obtained from the rat basilar artery were used for measurement of isometric force. The relaxant action of urocortin, CRF and sauvagine was studied in segments with a functionally intact endothelium. In segments precontracted with prostaglandin F 2α , urocortin, CRF and sauvagine induced concentration‐related relaxation. The order of potency was as follows (pD 2 ±s.e.m. given in brackets): urocortin (9.32±0.07) > sauvagine (9.08±0.08) > CRF (7.50±0.07). Complete relaxation was achieved with each agonist. Relaxation was not affected by removal of the endothelium but was markedly attenuated in segments precontracted with 50 m m K + Krebs solution. The relaxant effect of urocortin was inhibited by astressin in an apparently competitive manner. A pA 2 value of 7.52 was estimated for astressin. Inhibition of urocortin‐induced relaxation was also observed in the presence of the adenylate cyclase inhibitor SQ22536 (pD 2 in the presence of 300 μ m SQ22536, 9.36±0.05) and the K + channel blockers tetraethylammonium (10 m m ; pD 2 , 8.65±0.07), iberiotoxin (100 n m ; pD 2 , 8.88±0.08) and apamin (10 n m ; pD 2 , 8.94±0.07). However, the inhibitory actions of SQ22536 and apamin or iberiotoxin were not additive. The results suggest that urocortin induces relaxation of cerebral arteries by activating CRF‐R 2 receptors present in the vascular wall. Relaxation appears to be mediated by adenylate cyclase stimulation and activation of Ca 2+ ‐dependent K + channels. British Journal of Pharmacology (1998) 125 , 1164–1171; doi: 10.1038/sj.bjp.0702182