Abstract
The distribution and function of endothelin receptors in the guinea-pig urinary bladder were examined. Specific [ 125I]endothelin-1 binding sites with both the endothelin ET A and ET B receptor subtypes were distributed in the muscle layer. Endothelin-1 elicited a tonic contraction which was inhibited by cyclo( d-Asp-Pro- d-Val-Leu- d-Trp) (BQ123) but not by N- cis-2,6-dimethylpiperidinocarbonyl- l-γ-methylleucyl- d-1-methoxycarbonyltryptophanyl- d-norleucine (BQ788) and which was inhibited more strongly by a combination of BQ123 and BQ788. Sarafotoxin S6c elicited a contraction which was abolished by BQ788. The concentration of endothelin-1 in the muscle layer was 707.0±67.5 pg/g wet weight. Thus, endothelin-1 may regulate muscle tone via both subtypes of endothelin receptors in an autocrine manner in the guinea-pig urinary bladder.
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