Effects of a metalloendopeptidase-24.15. Inhibitor on renal hemodynamics and function in rats.

Abstract

/v"-[l-(ft.S)-carboxyl-3-phenylpropyl]-Ala-Ala-Phep-aminobenzoate (cFP-AAF-pAB), an active-site-directed inhibitor of metalloendopeptidase-24.15, has been shown to lower blood pressure, increase cardiac output and renal blood flow, and potentiate the intravenous bradykinin-induced vasodepressor response. Because in vivo cFP-AAF-pAB can be converted to A41-(R,S)-carboxyl-3-phenylpropyl]-Ala-Ala (a compound with angiotensin converting enzyme inhibitory activity) by metalloendopeptidase-24.11, it is possible that some of its effects are due to angiotensin converting enzyme inhibition. In the present study, we questioned (1) whether cFP-AAF-pAB inhibits angiotensin converting enzyme in vivo and (2) whether cFP-AAF-pAB has renal effects that are independent of its conversion to an angiotensin converting enzyme inhibitor. cFP-AAF-pAB alone (3 junol in 300 pL per rat) almost abolished the blood pressure response to angiotensin I, suggesting that in vivo it inhibits angiotensin converting enzyme. In rats pretreated with a high dose of enalaprilat (1 mg/kg), cFP-AAFpAB had no further effect on blood pressure, renal blood flow, or potentiation of the vasodepressor response to bradykinin but still increased glomerular filtration rate by 44±9% (P<.01); urine volume increased by 118±10% (P<.001), urinary sodium excretion by 230±31% (P<.001), urinary potassium excretion by 68±14% (P<.01), and urinary cyclic GMP by 55±18% (P<.01). All of these changes were significant compared with enalaprilat/vehicle-treated rats. Fractional excretion of sodium and potassium did not differ from controls. These results suggest that effects of cFP-AAF-pAB on blood pressure, renal blood flow, and potentiation of the vasodepressor response to bradykinin could be mediated by angiotensin converting enzyme inhibition. However, some of the renal effects may be due to inhibition of metalloendopeptidase-24.15 or peptidases other than angiotensin converting enzyme. Zn 2+ -containing neutral endopeptidase that is highly concentrated in the brain and testes but is also found in the kidney, heart, lung, and liver. 13In vitro, it degrades a variety of peptides such as bradykinin, angiotensin I (Ang I), neurotensin, and luteinizing hormone-releasing hormone (LHRH) and converts enkephalin-containing peptides into Leu-and Met-enkephalin.2 -4 In vivo, 7V-[l-(7?,S)-carboxyl-3-phenylpropylj-Ala-Ala-Phe-p-aminobenzoate (cFP-AAFpAB) blocks degradation of LHRH (a substrate for MEP-24.15); however, its physiological role in the metabolism of vasoactive peptides has not been determined. Genden and Molineaux 5 recently reported that inhibition of MEP-24.15 by cFP-AAF-pAB, an activesite-directed inhibitor, produced a marked fall in mean blood pressure (MBP) that was almost abolished by a kinin receptor antagonist. cFP-AAF-pAB also potentiated the bradykinin-induced vasodepressor response. In preliminary studies, lowers MBP and increases cardiac output, renal blood flow (RBF), and plasma kinins. A recent report 8 states that in vitro cFP-AAF-pAB competitively in...

Role of bradykinin receptors in the renal effects of inhibition of angiotensin converting enzyme and endopeptidases 24.11 and 24.15 in conscious rabbits

“…However, these effects are entirely attributable to inhibition of ACE by the metabolite cFP-AA (Telford et al, 1995;Lew et al, 1996). Similar observations have been made in anaesthetized rats in which the phenylalanine substituted analogue cFP-AAF-pAB was used (Yang et al, 1994). We can, however, be confident that the dose of cFP-AAY-pAB administered was sufficient to inhibit EP 24.15, since its plasma levels were orders of magnitude above its K, for EP 24.15 (16 nM; Orlowski et al, 1988).…”

“…We can, however, be confident that the dose of cFP-AAY-pAB administered was sufficient to inhibit EP 24.15, since its plasma levels were orders of magnitude above its K, for EP 24.15 (16 nM; Orlowski et al, 1988). In terms of effects on renal function, our observations contrast with those of Yang et al (1994), who found that in rats pretreated with only the ACE inhibitor enalaprilat, cFP-AAF-pAB increased glomerular filtration rate, urine volume, and the fractional excretion of Na'. There are a number of possible reasons for this discrepancy, including differences in experimental conditions between the two studies.…”

“…Certainly, in the present study in which cFP-AAY-pAB was administered as both a bolus and a slow infusion, blood levels remained sufficient to at least partially inhibit EP 24.11 (2.9-5.2 gM). We therefore conclude that on balance the evidence suggests that, at least under conditions where ACE and EP 24.11 are already inhibited, EP 24.15 plays little or no role in regulating renal function, and that the renal effects of cFP-AAF-pAB seen previously by Yang et al (1994) are probably attributable to inhibition of EP 24.1 1.…”

“…Thus, Yang et al (1994) studied anaesthetized rats with intact kidneys, while we used conscious uninephrectomized rabbits, in which renal function (particularly proximal tubular Na+ reabsorption) had changed to compensate for the reduced renal mass. Yang et al (1994) concluded from their study that 'cFP-AAFpAB might act on metalloendopeptidase 24.15 or peptidases other than ACE to inhibit degradation of vasoactive peptides that participate in the regulation of renal function'. We suggest, based on the results of our study, that a likely site of SCH 39370 cFP Captopril SCH 39370 Captopril Figure 4 Changes in systemic and renal haemodynamic variables following treatment with the EP 24.15 inhibitor cFP-AAY-pAB, in rabbits pretreated with a combination of the ACE inhibitor captopril and the EP 24.11 inhibitor, SCH 39370 and either the bradykinin antagonist Hoe 140 or its vehicle.…”

“…Since EP 24.15 is found in the kidney (Chu & Orlowski, 1985), and since bradykinin may be an important substrate for this enzyme , the potential role of EP 24.15 in renal bradykinin metabolism also merits investigation. Yang et al (1994) tested the effect of cFP-AAF-pAB on renal function in anaesthetized rats pretreated with the ACE inhibitor enalaprilat. They found that under these experimental conditions cFP-AAF-pAB increased glomerular filtration rate, urine output, and the urinary excretion of Na+ and K+.…”