Total serum angiotensin converting enzyme activity in rats and dogs after enalapril maleate (MK-421)

A centrifugal gel filtration separation of serum angiotensin converting enzyme (ACE) from a potent stable inhibitor is described. This, together with a 20 hr assay incubation of very dilute enzyme, permitted the assessment of the effects of enalapril maleate treatment on total serum ACE in rats and dogs. Total serum ACE increased in both species after 1 or 2 weeks at 10 mg/kg/day. Serum ACE in rats was more than doubled; whereas the increase was modest in dogs (48 +/- 9% minimum). The effect of the drug on serum ACE combined with inherent variability of ACE precluded use of serum ACE activity as an accurate measure of inhibitor concentration in animals receiving enalapril maleate.     

Tissue angiotensin I-converting enzyme activity in spontaneously hypertensive hamsters.

The purpose of this study was to measure angiotensin I-converting activity in heart, kidney, lung and cheek pouch tissue homogenates of spontaneously hypertensive and normotensive hamsters. We also determined inhibitor sensitivity and the effects of chloride anion concentration on kidney angiotensin I-converting activity in these animals. We found no significant differences in angiotensin I-converting activity between hypertensive and normotensive hamsters in all tissues tested. Inhibitor sensitivity of kidney angiotensin I-converting activity with captopril and lisonopril was similar in both groups. Finally, kidney angiotensin I-converting activity increased significantly in both groups as chloride anion concentration in the assay buffer increased. Substituting chloride anion for citrate abrogated the increase in angiotensin I-converting enzyme activity.     

Effect of Vaccinium ashei reade leaves on angiotensin converting enzyme activity in vitro and on systolic blood pressure of spontaneously hypertensive rats in vivo

The hypotensive effects of Vaccinium ashei reade (blueberry) leaves were studied in vitro and in vivo. Blueberry leaf showed a strong inhibitory effect on angiotensin-converting enzyme activity in vitro. Additionally, feeding of blueberry leaf suppressed the development of essential hypertension in spontaneously hypertensive rats in vivo. These results promise the use of blueberry leaf as a source of dietary hypotensive components.     

Temporal relationships of treatment with angiotensin converting enzyme inhibitors on the hypertension and cardiac hypertrophy in spontaneously hypertensive rats

Two groups of spontaneously hypertensive rats (SHRs) were treated with captopril and enalapril, respectively. Treatment was started at weaning and at 8 months of age. Blood pressure was maintained close to normal in rats treated from weaning and significantly lowered but not to normal levels in rats started on treatment at 8 months. The long-term treated rats did not show significant cardiac enlargement whereas those treated at 8 months had an increase in cardiac size although not to the same level as untreated animals. Treatment with minoxidil and minoxidil plus propranolol similarly lowers blood pressure, but does not reduce myocardial hypertrophy. The data confirm that both the time of onset of treatment as well as the type of drug influence the myocardial complications of hypertension in SHRs. These studies further demonstrate the use of the SHR as a model for clinical pharmacologic studies with antihypertensive agents.     

Oxidation-induced increase in activity of angiotensin converting enzyme in the rat kidney

The activity of angiotensin converting enzyme(ACE) in crude extracts of the rat renal cortex was increased when the oxidizing agent diamide was added to the extract. The maximal activity was obtained at concentrations over 1 mM, and the value was twice or more the activity in the absence of the pretreatment. The activity of ACE was also increased by the diamide-pretreatment of the isolated membrane fraction of the renal cortex, thereby indicating that the increase in activity was not due to oxidation of endogenous glutathione (GSH) that may lower the ACE activity, but rather that ACE itself was oxidized. When O2 was included in the extract for 2 h, the ACE activity also increased to about twice the original activity. Lineweaver-Burk plots analysis demonstrated that, after oxidation with diamide and O2, the Vmax was increased but the Km remained unchanged. We conclude that the action of ACE in the kidney functions may differ in relation to oxidation of the tissue.     

Effect of captopril (SQ 14225) on blood pressure,plasma renin activity and angiotensin I converting enzyme activity.

Seven patients with essential hypertension and seven patients with hypertension associated with renal artery stenosis received captopril (SQ 14225), an inhibitor of angiotensin I converting enzyme. There was a significant reduction in mean blood pressure, from 176/113 +/- 4/3 mm Hg during the control period to 140/90 +/- 5/3 mm Hg during captopril administration. Five patients received captopril alone and nine patients needed hydrochlorothiazide in addition to control their blood pressure. Captopril produced a significant increase in peripheral plasma renin activity. When measured 12 hours after the administration of captopril the angiotensin I converting enzyme activity was found to be similar to that during the control period even though the blood pressure was at or near normal. These findings indicate that although captopril is an effective antihypertensive agent, its action does not depend only on inhibition of plasma angiotensin I converting enzyme activity.     

Pharmacological properties of the converting enzyme inhibitor, enalapril maleate (MK-421)

Enalapril maleate (MK-421), an ethyl ester, is an angiotensin-converting enzyme (ACE) inhibitor from a novel series of substituted N-carboxymethyldipeptides. The parent diacid (MK-422) N-[(S)-1-carboxy-3-phenylpropyl]-L-Ala-L-Pro of MK-421 inhibited hog plasma ACE with an I50 of 1.2 nM. Because deesterification occurs slowly or not at all in vitro, the in vitro I50 for enalapril was 1200 nM. However, both enalapril and MK-422 were potent inhibitors of ACE by the i.v. and oral routes in rats and dogs. In rats with experimental hypertension, enalapril was most potent in those models in which the renin-angiotensin system plays a dominant role (salt restriction, two-kidney Grollman) and in models rendered renin dependent by diuretics, although blood pressure reduction did occur in low or normal renin models such as spontaneously hypertensive rats, in which inhibition of ACE as measured by the blockade of angiotensin I pressor responses bore little temporal relationship to the later fall in blood pressure after enalapril.     

Regulation of angiotensin converting enzyme activity in cultured human vascular endothelial cells

Angiotensin converting enzyme (ACE) of vascular endothelial cells is suggested to control vascular wall tonus through the conversion of angiotensin I (AI) to angiotensin II (AII) and the degradation of bradykinin. To obtain more insight into the pathophysiological significance of ACE of vascular endothelial cells, we studied the regulation of ACE produced by cultured human umbilical vein endothelial cells (EC). Phorbol 12-myristate 13-acetate (PMA) increased the cellular and medium ACE activity, accompanied by a marked morphological change in EC. N'-O'-dibutylyladenosine 3';5'-cyclic monophosphate (db-cAMP) increased only the cellular ACE activity and not the medium ACE activity. The effect of isoproterenol with 0.1mM theophylline mimicked that of db-cAMP. These findings suggest that PMA and cAMP-related agents participate in the control of vascular wall tonus through the positive regulation of ACE produced by vascular endothelial cells.     

Initial evaluation of the non-sulfhydryl-containing converting enzyme inhibitor MK-521 in hypertensive humans

MK-521 is a new orally active, nonsulfhydryl angiotensin-converting enzyme (ACE) inhibitor. Single doses of 2.5, 5.0, 10.0, and 20.0 mg were administered to nine hypertensive patients alternating with placebo. All doses of MK-521 caused profound suppression of ACE activity for more than 24 h and decreased standing diastolic blood pressure for more than 12 h without changes in pulse rate. Although there was no further reduction in blood pressure with doses above 5.0 mg, the duration of action was prolonged for more than 24 h with the higher doses. Serum MK-521 concentrations increased with dosage, and ACE was inhibited maximally at concentrations above 10 ng/ml. In this initial study, MK-521 was well tolerated and proved to be a potent and long-acting antihypertensive agent.     

The angiotensin I converting enzyme inhibitors, captopril and Wy-44,655 attenuate the consequences of cerebral ischemia in renovascular hypertensive rats

Global cerebral ischemia (four vessel model) was induced in renovascular hypertensive rats (two kidney, one clip model) chronically treated with intraperitoneal administration of angiotensin I converting enzyme inhibitors, either captopril (100 mg/kg per day) or Wy-44,655 (10 mg/kg per day). Mortality following cerebral ischemia was higher in renovascular hypertensive rats than in normotensive controls. Reduction of blood pressure with captopril or Wy-44,655, lowered mortality. In surviving renovascular hypertensive and normotensive rats cerebral ischemia induced hyperactivity and lesions of the CA1 area of the hippocampus. Prolonged treatment with captopril--but not with Wy-44,655--reduced hyperactivity and the extent of the CA1 lesions. In conclusion, hypertension increases mortality following cerebral ischemia but does not affect the extent of brain injury in survivors. Prior treatment with converting enzyme inhibitors lowers mortality. Treatment with captopril attenuates brain injury in survivors.     

Schistosoma mansoni: angiotensin converting enzyme activity in mice under the influence of praziquantel and/or captopril.

Murine schistosomiasis is usually associated with hepatic granulomatous lesions together with high serum and granuloma angiotensin converting enzyme (ACE) activity. Praziquantel (PRZ) which is known to reduce granuloma size was studied to show whether this effect is related to changes in ACE activity. Furthermore, captopril was studied to show whether by inhibiting ACE activity, the drug could also affect granuloma size. PRZ, captopril, and their combination led to significant reduction in liver granuloma. However, in normal mice, captopril was shown to increase rather than decrease serum ACE. The decrease in ACE activity by PRZ was correlated with its curative effect in infected mice. However, in experimentally induced pulmonary granulomata, the drug reduced granuloma size without affecting ACE activity of either serum or granuloma. It may be concluded that reduction in ACE activity may be beneficial as far as diminution of granuloma size is concerned and irrespective of whether there is an active infection or not. The possible use of Captopril as an antihypertensive in bilharzial infections associated with hypertension would probably not adversely affect the granulomatous lesions.     

The angiotensin converting enzyme inhibitor captopril reduces oviposition and ecdysteroid levels in Lepidoptera

The role of angiotensin converting enzyme (ACE, peptidyl dipeptidase A) in metamorphic- and reproductive-related events in the Egyptian cotton leafworm, Spodoptera littoralis (Lepidoptera, Noctuidae) was studied by using the selective ACE inhibitor captopril. Although oral administration of captopril had no effect on larval growth, topical administration to new pupae resulted in a large decrease of successful adult formation. Oviposition and overall appearance of adults emerging from treated larvae did not differ significantly from those emerging from non-treated larvae. In contrast, topical or oral administration of captopril to newly emerged adults caused a reduction in oviposition. By evaluating the effect of captopril on ecdysteroid titers and trypsin activity, we revealed an additional physiological role for ACE. Captopril exerted an inhibitory effect on ecdysteroid levels in female but not in male adults. Larvae fed a diet containing captopril exhibited increased trypsin activity. A similar captopril-induced increase in trypsin activity was observed in female adults. In male adults, however, captopril elicited reduced levels of trypsin activity. Our results suggest that captopril downregulates oviposition by two independent pathways, one through ecdysteroid biosynthesis regulation, and the other through regulation of trypsin activity. Apparently, fecundity is influenced by a complex interaction of ACE, trypsin activity, and ecdysteroid levels.     

Effects of captopril on acute phase in two-kidney Goldblatt hypertensive rats and spontaneously hypertensive rats]

Effects of continuous oral administration of captopril were investigated on acute phase in two-kidney Goldblatt hypertensive (2 KGH) rats and spontaneously hypertensive rats (SHR). Systolic blood pressure gradually rose throughout the experimental period of 7, 14, 21 and 28 days in both 2 KGH rats and SHR. These gradual increases of systolic blood pressure were reduced by administration of captopril in both rats. Plasma renin activity were markedly increased throughout the experimental period in both rats treated with captopril, and were modestly increased in 2 KGH rats. In contrast, those changes in plasma renin activity were not obvious in SHR. In 2 KGH rats, juxtaglomerular index (JGI) and juxtaglomerular cell count (JGCC) of the clipped kidneys increased whereas JGI of the opposite kidneys decreased. In contrast, those changes in JGI and JGCC were not obvius in SHR. On the other hand, JGI and JGCC of the clipped kidneys increased in 2 KGH rats treated with captopril and those of the both kidneys increased in SHR treated with captopril. These results suggested that juxtaglomerular cells were related to the development of hypertension in 2 KGH rats, but were not clear in SHR. And these results were found that captopril showed antihypertensive effects, in spite of rises in JGI and JGCC of both 2 KGH rats and SHR.     

Endogenous inhibitor of angiotensin converting enzyme in the rat heart

We have identified a substance in the rat heart which inhibits ACE. This substance was characterized to be a sulfhydryl (SH) protein, the SH moiety being essential for the inhibitory activity. The inhibitory activity disappeared when the extract was boiled, or the ultrafiltrate(mol.wt.less than 10,000) was used, or when the extract was pretreated with the SH-blocking agent 5,5'-dithiobis-(2-nitro benzoic acid) at 0.5mM or the SH oxidizing agent diamide at 1mM. This substance was fractionated with Thiopropyl Sepharose affinity chromatography, precipitation with 40% ammonium sulfate saturation and high performance liquid chromatography. The mode of inhibition was competitive. In the presence of 20 micrograms/ml of this substance, the contraction of rat aortic strips induced by 5 x 10(-8)M ANG I was inhibited by 60%. This endogenous inhibitor of ACE may modulate the activity of ACE in the heart, in response to alterations in the oxidation-reduction balance in the tissue.     

Effect of converting enzyme inhibition with captopril on baroreflex sensitivity

Clinical and experimental data suggest that both Captopril and angiotensin II (AII) reduce baroreflex responsiveness, and the main action of this converting enzyme inhibitor (CEI) seems clear to suppress AII synthesis. The aim of this work is to investigate this striking similarity of effects. We have verified that CEI (4 mg/kg) originates tachycardia significantly lower (P less than 0.001) than that produced in response to a similar hypotension elicited by an unspecific vasodilator: sodium nitroprusside (10-45 micrograms/kg min). CEI SQ 20881 has been reported to increase plasma vasopressin concentrations (AVP); this peptide is also known to modify baroreflex responses and has a small direct negative chronotropic effect. However, our determinations of AVP do not show any difference between the control group and the group treated with Captopril (4.78 +/- 0.87 and 5.26 +/- 0.19 pg/ml respectively). On the other hand, although CEI did not modify the rapid responses of heart rate (HR) to changes of mean arterial pressure (MAP), the decrease of MAP induced by nitroprusside was higher in the group treated with Captopril than in control group; it could mean a baroreflex ability decrease to buffer the hypotension. However, AII elicited a strong impairment of both rapid responses of HR and the buffering of hypotension produced by NP, these actions being suggested as centrally mediated. These results could indicate that the suppression of peripheral AII synthesis and therefore, the lack of pre- and postjunctional sympathetic potentiation owing to this hormone, is responsible for the absence of tachycardia under Captopril treatment.     

Effect of chronic colchicine administration on the myocardium of the aging spontaneously hypertensive rat

Colchicine has been demonstrated to suppress the release of fibroblast growth factors, retard collagen formation and augment collagenase activity. Trials with colchicine in patients with hepatic fibrosis have suggested clinical benefit. The development of impaired myocardial function in the spontaneously hypertensive rat (SHR) is associated with a marked increase in myocardial fibrosis. The present study was carried out to test the hypothesis that chronic colchicine administration to the SHR would prevent the development of fibrosis and impaired myocardial performance.Colchicine (1 mg/l drinking water) was administered to male SHR and WKY rats from at age 13 months until 24 months or until evidence of heart failure was observed. Age-matched untreated SHR and colchicine treated and untreated WKY served as controls. At study, active and passive properties of isolated left ventricular muscle preparations were determined. Myocardial fibrosis was assessed by measuring hydroxyproline and histologic determination of interstitial cross-sectional area. Increases in LV hydroxyproline and interstitial area were found in untreated SHR relative to WKY; passive myocardial stiffness was increased and active muscle properties were depressed. In comparing colchicine treated vs untreated SHR, no differences in hydroxyproline, interstitial area or intrinsic myocardial function were found. In the WKY, colchicine increased myocardial interstitium and passive stiffness without changing hydroxyproline. Active myocardial function was not depressed.Thus, chronic colchicine administration neither attenuated the development of interstitial fibrosis nor prevented impaired myocardial function in the SHR. Colchicine treatment was associated with increased interstitium in WKY with increased passive myocardial stiffness. (Mol Cell Biochem 166: 45-54, 1997)     

Species differences in the angiotensin converting enzyme activity of mammalian serum

Angiotensin converting enzyme (ACE; EC 3. 4. 15. 1) activities were compared in the serum of various mammals. Cattle, human, monkey, and swine serum showed enzyme levels from 3.7 to 67 mU/ml. Relatively high enzyme activity was observed in rodents, the rat (Wistar) and mouse (BALB/c) showing levels of 93 +/- 7 and 1052 +/- 165 mU/ml, respectively. Among the mammalian sera examined, that of the guinea pig contained the highest ACE level, 2262 +/- 574 mU/ml. No age-related difference in enzyme activity was observed in 10-day-old to 1-year-old guinea pigs.     

Feeding blueberry diets inhibits angiotensin II-converting enzyme (ACE) activity in spontaneously hypertensive stroke-prone rats

Feeding flavonoid-rich blueberries to spontaneously hypertensive stroke-prone rats (SHRSP) lowers blood pressure. To determine whether this is due to inhibition of angiotensin-converting enzyme (ACE) activity, as seen with other flavanoid-rich foods, we fed blueberries to SHRSP and normotensive rats and analyzed ACE activity in blood and tissues. After 2 weeks on a control diet, the hypertensive rats showed 56% higher levels of ACE activity in blood as compared with the normotensive rats (p < 0.05). Feeding a 3% blueberry diet for 2 weeks lowered ACE activity in the SHRSP (p < 0.05) but not the normotensive rats. ACE activity in plasma of SHRSP was no longer elevated at weeks 4 and 6, but blueberry feeding inhibited ACE in SHRSP after 6 weeks. Blueberry diets had no effect on ACE activity in lung, testis, kidney, or aorta. Our results suggest that dietary blueberries may be effective in managing early stages of hypertension, partially due to an inhibition of soluble ACE activity.