enalaprilat-anhydrous and trandolaprilat

The present study was undertaken to determine whether trandolaprilat, an active form of angiotensin I converting enzyme (ACE) inhibitor, may improve ischemia/reperfusion-induced contractile dysfunction and metabolic derangement of isolated rat hearts. Ischemia (25 min) and subsequent 60-min reperfusion resulted in a small recovery of post-ischemic left ventricular developed pressure (LVDP), a sustained increase in left ventricular end-diastolic pressure, an increase in the release of creatine kinase and ATP metabolites from the perfused heart, and changes in myocardial sodium, potassium, calcium and magnesium contents. Treatment with 10-100 microM of trandolaprilat for the last 10 min of pre-ischemia recovered approximately 50-90% of pre-ischemic LVDP during reperfusion, whereas that with 30-100 microM of enalaprilat restored approximately 55-65% of the pre-ischemic LVDP. Treatment with either trandolaprilat or enalaprilat at these concentrations attenuated the release of creatine kinase and ATP metabolites into the perfusate during reperfusion. Treatment with 30 microM trandolaprilat suppressed ischemia/reperfusion-induced changes in myocardial ion content. Treatment with bradykinin during the last 10 min of pre-ischemia also resulted in a post-ischemic contractile recovery with a degree similar to that of the trandolaprilat-treated hearts. E4177, an AT1-antagonist, showed no effect on ischemia/reperfusion-induced changes in cardiac parameters. The enhancement of post-ischemic contractile recovery by the ACE inhibitor was abolished by treatment with either Hoechst 140, a bradykinin (BK2) antagonist, or diclofenac, a cyclooxygenase inhibitor. These results suggest that trandolaprilat is capable of attenuating ischemia/reperfusion injury of isolated perfused hearts and altered BK metabolism is, at least in part, involved in this effect.

Topics: Adenosine Triphosphate; Analysis of Variance; Angiotensin Receptor Antagonists; Angiotensin-Converting Enzyme Inhibitors; Animals; Bradykinin; Bradykinin Receptor Antagonists; Cations; Creatine Kinase; Enalaprilat; Indoles; Male; Myocardial Contraction; Myocardial Reperfusion Injury; Rats; Rats, Wistar; Treatment Outcome

The effects of 14-day trandolapril or enalapril treatment of spontaneously hypertensive rats (SHRs) were studied on blood pressure and angiotensin-converting enzyme (ACE) activity measured ex vivo in various organs. Both ACE inhibitors caused dose-dependent decreases in blood pressure and ACE activity, trandolapril being 30- and 400- to 1,000-fold more active than enalapril on blood pressure and ACE activity, respectively. However, comparison of ACE inhibitory activities of the diacid forms of trandolapril and enalapril, i.e., trandolaprilat and enalaprilat, measured in vitro on various tissues, showed that trandolaprilat was only three- to fivefold more active than enalaprilat. To understand the reasons for such discrepancies between ex vivo effects of ACE inhibitors and in vitro actions of their diacid metabolites, we measured the lipophilicities of the compounds and investigated the possibility that trandolapril could display an ACE inhibitory effect by itself. Trandolaprilat was found to be far more lipophilic than enalaprilat, as shown by reverse-phase high-performance liquid chromatography studies performed at pH 7.4 (log kw7.4 = 1.487 vs. 0.108). In addition, trandolapril was practically as active in vitro as its diacid metabolite (IC50 = 2.5 vs. 1.35 nM) in inhibiting ACE activity in the aorta, whereas enalapril was practically devoid of any effect (IC50 = 240 nM). Measurements of relative affinities of inhibitors or metabolites for purified human renal ACE showed that trandolapril displayed about 20% of the affinity of its diacid metabolite (IC50 = 15 vs. 3.2 nM); enalaprilat affinity (34 nM) was within the same range as those of trandolapril and trandolaprilat, whereas enalapril displayed a very low affinity for the purified enzyme (IC50 = 50 microM).(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Angiotensin-Converting Enzyme Inhibitors; Animals; Blood Pressure; Enalapril; Enalaprilat; Indoles; Isoquinolines; Male; Peptidyl-Dipeptidase A; Rats; Rats, Inbred SHR; Solubility; Tetrahydroisoquinolines

1. Trandolaprilat was found to inhibit angiotensin I (Ang I)-induced contraction of the rat thoracic aorta, and to augment bradykinin(BK)-induced contraction of the guinea pig ileum. In inhibitory activity (IC50) on the Ang I induced contraction of the rat thoracic aorta, trandolaprilat was about 2.4 times as potent as enalaprilat. Concerning the augmenting activity (AC50) on bradykinin-induced contraction of the guinea pig ileum, the activity of trandolaprilat was similar to that of enalaprilat. 2. Trandolaprilat had no effect on contractions induced by norepinephrine, PGF2 alpha, 5-HT or CaCl2 in the thoracic aorta of rats. 3. Trandolaprilat produced endothelium-dependent relaxation. This relaxation was inhibited by NG-methyl-L-arginine treatment, suggesting that endothelium-dependent relaxation of trandolaprilat is related to endothelium-derived-relaxation-factor(EDRF/NO). Like trandolaprilat, captopril also produced endothelium-dependent relaxation, whereas enalaprilat had no effect.

Topics: Angiotensin I; Angiotensin-Converting Enzyme Inhibitors; Animals; Aorta, Thoracic; Arginine; Bradykinin; Enalaprilat; Endothelium, Vascular; Guinea Pigs; Ileum; In Vitro Techniques; Indoles; Male; Muscle Contraction; Muscle, Smooth; Muscle, Smooth, Vascular; omega-N-Methylarginine; Rats; Rats, Wistar

The endothelial angiotensin I-converting enzyme (ACE; EC 3.4.15.1) has recently been shown to contain two large homologous domains (called here the N and C domains), each being a zinc-dependent dipeptidyl carboxypeptidase. To further characterize the two active sites of ACE, we have investigated their interaction with four competitive ACE inhibitors, which are all potent antihypertensive drugs. The binding of [3H] trandolaprilat to the two active sites was examined using the wild-type ACE and four ACE mutants each containing only one intact domain, the other domain being either deleted or inactivated by point mutation of the zinc-coordinating histidines. In contrast with all the previous studies, which suggested the presence of a single high affinity inhibitor binding site in ACE, the present study shows that both the N and C domains of ACE contain a high affinity inhibitor binding site (KD = 3 and 1 X 10(-10) M, respectively, at pH 7.5, 4 degrees C, and 100 mM NaCl). Chloride stabilizes the enzyme-inhibitor complex for each domain primarily by slowing its dissociation rate, as the k-1 values of the N and C domains are markedly decreased (about 30- and 1100-fold, respectively) by 300 mM NaCl. At high chloride concentrations, the chloride effect is much greater for the C domain than for the N domain resulting in a higher affinity of this inhibitor for the C domain. In addition, the inhibitory potency of captopril (C), enalaprilat (E), and lisinopril (L) for each domain was assayed by hydrolysis of Hip-His-Leu. Their Ki values for the two domains are all within the nanomolar range, indicating that they are all highly potent inhibitors for both domains. However, their relative potencies are different for the C domain (L greater than E greater than C) and the N domain (C greater than E greater than L). The different inhibitor binding properties of the two domains observed in the present study provide strong evidence for the presence of structural differences between the two active sites of ACE.

Topics: Angiotensin I; Angiotensin-Converting Enzyme Inhibitors; Animals; Binding Sites; Captopril; Chlorides; CHO Cells; Cricetinae; Enalapril; Enalaprilat; Humans; Indoles; Kinetics; Lisinopril; Mutation; Peptidyl-Dipeptidase A