Characterization of angiotensin II formation in human isolated bladder by selective inhibitors of ACE and human chymase: a functional and biochemical study

Abstract

1 Functional recordings of smooth muscle tension and biochemical experiments on membrane fractions were performed to characterize angiotensin II (AII) formation in human isolated bladder smooth muscle. 2 A novel human chymase inhibitor CH 5450 (Z-Ile-Glu-Pro-Phe-CO 2 Me) and a recently developed human chymase substrate Pro 11 -,D-Ala 12 )-angiotensin I, claimed to be resistant to angiotensin converting enzyme (ACE) and carboxypeptidase, were used. 3 Angiotensin I (AI) (0.3 mM) induced a contractile response amounting to 58+5% (n=12) of the initial K + (124 mM)-induced contractions. This response was reduced to 36+3% (n=8) by the ACEinhibitor enalaprilat (10 mM), while pretreatment with soybean trypsin inhibitor (STI 200 mg ml 71 ) or CH 5450 (10 mM) had no eect. However, the combination of enalaprilat and STI reduced the AIinduced contractions to 19+5% (n=6), and the combination of enalaprilat and CH 5450 caused an almost complete inhibition of the AI-induced contractions to 1+1% (n=6). )-AI-induced contractions to 34+5% (n=6) and 24+4% (n=6), respectively. The combination of enalaprilat and STI or enalaprilat and CH 5450 did not produce any further inhibition. 5 Experiments with detrusor membrane fractions incubated with AI (50 mM) were performed. In the presence of enalaprilat (100 mM), carboxypeptidase inhibitor CPI (10 mg ml 71 ) and aprotinin (15 mM), CH 5450 (10 nM ± 1 mM) caused a concentration-dependent inhibition of AII formation. 6 The results con®rm that AII is a potent contractile agent in the human isolated detrusor muscle. They also indicate that the serine protease responsible for AII formation in the human bladder in vitro is human chymase or an enzyme similar to human chymase.

Functional role, cellular source, and tissue distribution of rat elastase-2, an angiotensin II-forming enzyme

“…2 and 3). Previous reports have indicated two shortcomings inherent in this approach to reveal the predominance of ACE and non-ACE pathways in different experimental models: first, the outcome is highly dependent on the concentrations of the substrate used, with higher concentrations favoring the apparent contribution of non-ACE pathways (26); and second, the overcapacity among the ANG II generating proteases tends to diminish the relative importance of selectively inhibited enzymes (61). Notwithstanding, the synergistic inhibitory effects of captopril and chymostatin (Fig.…”

“…In other investigations, the partial or total blockade of ANG II formation by different combinations of ACE inhibitors with chymostatin or other protease inhibitors has provided clues as to the nature of the enzymes involved in ANG I conversion in a particular tissue or pharmacological preparation (23,45). Since the advent of [Pro 11 ,D-Ala 12 ]-ANG I, a biologically inactive precursor that selectively yields ANG II on incubation with chymases but not with ACE or carboxypeptidases (22), several reports (18,22,26,38,41,43,61,63) have described the relative contribution of chymases in ANG II formation in isolated preparations derived from various species.The vascular endothelium actively participates in the control of vascular tone through the synthesis and metabolism of several vasoactive substances (1). In particular, the vascular endothelium has been shown to be a major site of conversion of circulating ANG I to ANG II by ACE located on its luminal surface (2).…”

Pharmacology of the Lower Urinary Tract: Basis for Current and Future Treatments of Urinary Incontinence

“…Angiotensins. An autocrine/paracrine reninangiotensin system has been identified in the urinary bladder (Weaver-Osterholtz et al, 1996), and angiotensin II (ATII) formation was demonstrated in human isolated detrusor smooth muscle Lindberg et al, 1994;Waldeck et al, 1997). ATII receptors have been demonstrated by different methods in animal as well as human detrusor (Anderson et al, 1984;Lam et al, 2000).…”

“…ATII was reported to contract the urinary bladder of several species, but with a wide range of relative potencies (Erspamer et al, 1973;Anderson et al, 1984). Several investigators (Erspamer et al, 1981;Andersson et al, 1992, Saito et al, 1993Lindberg et al, 1994;Waldeck et al, 1997), but not all , have shown that in human detrusor muscle, ATII was a potent and effective contractile agent. In dog bladder, the responses to both ATII and ATI were minor or lacking (Steidle et al, 1990), illustrating the wide variation in response to the peptide between species.…”

The Effects of Some Neuropeptides on Motor Activity of Smooth Muscle Organs in Abdominal and Pelvic Cavities

“…Local tissue RAS was found in the blood vessels, heart, kidneys, small intestines, pancreatic tissue, liver, ovaries and brain (Paul at al., 2006). Other enzymes involved in RAS and physiologicaly active metabolites of Ang I and Ang II were also found (Waldeck et al, 1997;Miyazaki & Takai, 2006).…”