Effects of combined neutral endopeptidase 24-11 and angiotensin-converting enzyme inhibition on femoral vascular conductance in streptozotocin-induced diabetic rats

Abstract

1. The successive effects of the angiotensin-converting enzyme inhibitor captopril (CAP, 2 mg kg(-1)+1 mg kg(-1) 30 min(-1) infusion) and the neutral endopeptidase 24-11 inhibitor retrothiorphan (RT, 25 mg kg(-1)+12.5 mg kg(-1) 30 min(-1) infusion) were studied on femoral vascular conductance (FVC) in streptozotocin-induced diabetic (STZ-SD) and control Sprague-Dawley (C-SD) rats. The role of the kinin-nitric oxide (NO) pathway was assessed by (1) using pre-treatments: a bradykinin (BK) B2 receptor antagonist (Hoe-140, 300 microg kg(-1)), a NO-synthase inhibitor (N(omega)-nitro-L-arginine methyl ester, L-NAME, 10 mg kg(-1)), a kininase I inhibitor (DL-2-mercaptomethyl-3-guanidinoethylthiopropanoic acid, MGTA, 10 mg kg(-1)+20 mg kg(-1) 20 min(-1) infusion) and (2) comparing the effects in STZ-induced diabetic (STZ-BN) and control Brown-Norway kininogen-deficient (C-BN) rats. 2. In C-SDs, CAP and CAP+RT increased FVC similarly. In STZ-SDs, FVC and FBF were decreased compared to C-SDs. CAP+RT increased them more effectively than CAP alone. 3. In both C-SDs and STZ-SDs, the femoral bed vasodilatation elicited by CAP was inhibited by Hoe-140 and L-NAME. The FVC increase elicited by CAP+RT was not significantly reduced by Hoe-140 but was inhibited by L-NAME and Hoe-140+MGTA. 4. In C-BNs, the vasodilatator responses to CAP and CAP+RT were abolished and highly reduced, respectively. In STZ-BNs, these responses were abolished. 5. These results show that in STZ-SDs, CAP+RT improve FBF and FVC more effectively than CAP alone. These effects are linked to an increased activation of the kinin-NO pathway. BK could lead to NO production by BK B2 receptor activation and another pathway in which kininase I may be involved.

Figure 1

Effects of captopril (CAP, 2 mg kg⁻¹, i.v.+1 mg kg⁻¹ 30 min⁻¹ infusion) alone and in combination with retrothiorphan (RT, 25 mg kg⁻¹, i.v.+12.5 mg kg⁻¹ 30 min⁻¹ infusion) on (a) mean arterial pressure, (b) femoral blood flow and (c) femoral vascular conductance in control (C-SD, n=6) and diabetic (STZ-SD, n=5) Sprague-Dawley rats. For each rat, values measured at 20, 25 and 30 min after the start of each infusion are averaged. Each column represents the mean value and the T bar the s.e.m. ^**P<0.01 and ^***P<0.001 vs baseline; †P<0.05, ††P<0.01 and †††P<0.001 vs CAP alone (ANOVA for repeated measures followed by Newman-Keuls test).

Figure 2

Effects of Hoe-140 (H, 300 μg kg⁻¹, i.v.), MGTA (M, 10 mg kg⁻¹, i.v.+20 mg kg⁻¹ 20 min⁻¹ infusion), Hoe-140+MGTA (H+M) and L-NAME (LN, 10 mg kg⁻¹, i.v.) on changes in (a) mean arterial pressure, (b) femoral blood flow and (c) femoral vascular conductance evoked by successive administration of captopril (CAP, 2 mg kg⁻¹, i.v.+1 mg kg⁻¹ 30 min⁻¹ infusion) and retrothiorphan (RT, 25 mg kg⁻¹, i.v.+12.5 mg kg⁻¹ 30 min⁻¹ infusion) in control Sprague-Dawley rats (C-SDs). For each rat, values measured at 20, 25 and 30 min after the start of each infusion are averaged. Each column represents the mean value of n rats and the vertical T bar the s.e.m. ^*P<0.05 and ^**P<0.01 vs CAP without pre-treatment or vs CAP+RT without pre-treatment (ANOVA followed by Dunnett's t-test).

Figure 3

Effects of Hoe-140 (H, 300 μg kg⁻¹, i.v.), MGTA (M, 10 mg kg⁻¹, i.v.+20 mg kg⁻¹ 20 min⁻¹ infusion), Hoe-140+MGTA (H+M) and L-NAME (LN, 10 mg kg⁻¹, i.v.) on changes in (a) mean arterial pressure, (b) femoral blood flow and (c) femoral vascular conductance evoked by successive administration of captopril (CAP, 2 mg kg⁻¹, i.v.+1 mg kg⁻¹ 30 min⁻¹ infusion) and retrothiorphan (RT, 25 mg kg⁻¹, i.v.+12.5 mg kg⁻¹ 30 min⁻¹ infusion) in diabetic Sprague-Dawley rats (STZ-SDs). For each rat, values measured at 20, 25 and 30 min after the start of each infusion are averaged. Each column represents the mean value of n rats and the vertical T bar the s.e.mean. ^*P<0.05 and ^**P<0.01 vs CAP without pre-treatment or vs CAP+RT without pre-treatment (ANOVA followed by Dunnett's t-test).

Figure 4

Effects of captopril (CAP, 2 mg kg⁻¹, i.v.+1 mg kg⁻¹ 30 min⁻¹ infusion), alone and in combination with retrothiorphan (RT, 25 mg kg⁻¹, i.v.+12.5 mg kg⁻¹ 30 min⁻¹ infusion), on (a) mean arterial pressure, (b) femoral blood flow and (c) femoral vascular conductance in control (C-BN, n=7) and diabetic (STZ-BN, n=4) Brown-Norway kininogen-deficient rats. For each rat, values measured at 20, 25 and 30 min after the start of each infusion are averaged. Each column represents the mean value and the T bar the s.e.mean. ^*P<0.05, ^**P<0.01 and ^***P<0.001 vs baseline; †††P<0.001 vs CAP alone (ANOVA for repeated measures followed by Newman-Keuls test).