Pharmacological characterization of RMP-7, a novel bradykinin agonist in smooth muscle

RMP-7 is a bradykinin (BK) agonist designed to be resistant to kininases such as angiotensin-converting enzyme (ACE). Pharmacological assays were performed with RMP-7 in isolated guinea-pig ileum and rat mesenteric artery. RMP-7 induced contractile responses in the guinea-pig ileum, where the apparent affinity of the peptide (pD(2)) was significantly lower than that determined for BK (7.3 +/- 0.07 vs. 8.3 +/- 0.05, respectively). HOE-140 blocked this effect indicating that B-2 receptor was involved. Captopril (1 mu M) had no potentiating effect on RMP-7 but increased pD(2) value determined for BK (8.8 +/- 0.1), confirming a high resistance of RMP-7 to the ACE. in rat mesenteric artery, RMP-7 induced endothelium-dependent relaxation (7.8 +/- 0.4), with a higher affinity than that of BK which induced vasodilatation only in the presence of 1 mu M captopril (6.9 +/- 0.36). Nevertheless, the maximum effect induced by RMP-7 was lower than that of BK in contrast to that observed in guinea-pig ileum although B-2 receptor was involved in both cases. We concluded that: RMP-7 is greatly resistant to the ACE and that the receptor sites activated by RMP-7 and BK show important differences in vascular and non-vascular preparations probably due to the different sensitivity of the B-2 receptor to RMP-7. (C) 1999 Elsevier Science B.V. All rights reserved.Escola Paulista Med, Dept Biophys, BR-04023062 São Paulo, BrazilEscola Paulista Med, Dept Biophys, BR-04023062 São Paulo, BrazilWeb of Scienc

Evidence for changes in the tachyphylactic property of recombinant angiotensin II AT(1) receptor expressed in CHO cells

The manifestation of tachyphylaxis to angiotensin 11 in Chinese hamster ovary (CHO) cells expressing the rat angiotensin II AT(1) receptor was investigated. the cells were transfected with a cDNA fragment containing the complete coding region of the angiotensin II AT(1A) receptor gene, as well as 56 bp of its 3'- and 52 bp of its 5-untranslated regions. These cells (CHO-AT(1)) responded to angiotensin 11 by increases in intracellular Ca2+ concentration and inositol phosphate turnover, which were inhibited upon repeated administrations, characterizing the tachyphylaxis phenomenon. in contrast to smooth muscle cells, which are rendered tachyphylactic to angiotensin H but not to [2-lysine]angiotensin 11 ([Lys(2)]angiotensin 11), this analogue induced responses in CHO-AT(1) cells that were also inhibited upon repeated administrations. A smooth muscle cell line, which showed tachyphylaxis only to angiotensin II, became tachyphylactic also to [Lys2]angiotensin 11 after transfection with the angiotensin 11 AT(1) receptor gene. Our findings suggest that posttranscriptional control directed by the 3'- or the 5'-untranslated regions in the angiotensin 11 AT(1) receptor gene may play a role in modulating the signal transduction pathways involved in the mechanism of angiotensin 11 tachyphylaxis. (C) 2002 Elsevier Science B.V. All rights reserved.Universidade Federal de São Paulo, Dept Biophys, Escola Paulista Med, BR-04023060 São Paulo, BrazilUniversidade Federal de São Paulo, Dept Biophys, Escola Paulista Med, BR-04023060 São Paulo, BrazilWeb of Scienc