Lung Angiotensin Converting Enzyme Activity Research Articles

Correlative morphological and biochemical studies on monocrotaline-induced pulmonary alterations in rats

A single s.c. injection of 60 mg/kg of monocrotaline to rats induced pulmonary alterations characterized by hyaline thrombi of capillaries and arterioles, focal necrosis of alveolar walls, and medial thickening and intimal hyalinosis of arteries. Such pathological alterations became apparent 7 days after injection and thereafter progressively developed with the passage of time. Histometrical examination revealed a reduction of the alveolar surface area in a unit volume of lung tissue in these rats. Biochemically, lung angiotensin-converting enzyme activity was estimated to have reduced in parallel with the development of pulmonary alterations while plasma angiotensin-converting enzyme activity was unchanged throughout the experimental period.

The effect of morphine, naloxone, D- and L-aspartic acid on the brain and lung ACE in mice

The brain and lung angiotensin converting enzyme (ACE) activities of the mice injected with 10 mg/kg morphine and/or naloxone, 200 mg/kg D- and/or L-aspartic acid were spectrophotometrically determined. Morphine, naloxone, D- and L-aspartic acid alone inhibited both brain and lung ACE activities whereas the combinations of morphine with naloxone, D-aspartic acid with L-aspartic acid and morphine with naloxone + L-aspartic acid showed no inhibitory effect on the brain ACE. While naloxone or L-aspartic acid partly antagonized the suppression of morphine on the lung ACE their combination completely prevented morphine from inhibiting the lung ACE. In the in vivo experiments performed on the brain and lung homogenates of the untreated mice the determination of the ACE activity in the incubating media containing 3.10(-3) M morphine or naloxone, 10(-2) M D- or L-aspartic acid showed a significant decrease in the activity. But no in vitro antagonistic effect was found by using the combinations of the drugs used in the study. The antagonism seen in the in vivo experiments was considered as an indirect one. And the relationship between the inhibitory effect of morphine, naloxone and D-aspartic acid, their suppressive effect on drinking and their beneficial effects in various forms of shock was discussed.

Radiation Injury in Rat Lung: II. Angiotensin-Converting Enzyme Activity

To determine the role of endothelial dysfunction in the pathogenesis of radiation-induced pulmonary injury, lung angiotensin-converting enzyme (ACE) activity, arterial perfusion, and ultrastructure were examined from 1 to 150 days after a single exposure of 25 Gy of 60Co gamma rays to the right hemithorax of rats. Arterial perfusion to the irradiated right lung increased during the first 2 weeks, then decreased to approximately 80% of the left lung value at 30 days postirradiation. Perfusion of the irradiated lung continued to decline, and by 90-150 days was only 40% of that of the shielded lung. ACE activity in the irradiated right lung did not change significantly until 30 days after exposure, when it decreased to 72% of that in the left lung. ACE activity in the right lung declined steadily from 30 to 90 days postirradiation, then reached a plateau through 150 days at less than 20% of normal. Perivascular and interstitial edema was evident at 1 day after irradiation and persisted for 30 days. Endothelial cells exhibited blebbing, fragmentation, and increased basement membrane at 30 days. Mast cells were present in the septa, but interstitial collagen was not increased at that time. From 90 to 150 days postexposure, progressive obliteration of capillaries by fibrotic reactions was observed. Thus decreased ACE activity accompanies radiation-induced hypoperfusion and endothelial ultrastructural changes in rat lung. All of these reactions precede the development of pulmonary fibrosis.

Pulmonary endothelial dysfunction in the presence or absence of interstitial injury induced by intratracheally injected bleomycin in rabbits.

Previously, we reported that repeated subcutaneous administration of bleomycin (BLM) to rabbits produced functional and structural endothelial damage with no evidence of interstitial fibrosis. In the present study, rabbits received intratracheally a single injection of BLM (6 units/kg, n = 6: "low dose" or 11 units/kg, n = 4: "high dose"); 6 additional animals received intratracheally an injection of saline and served as controls. Four weeks after BLM administration, the low-dose group demonstrated significant reduction in the single-pass pulmonary removal of 14C-5-hydroxytryptamine (5-HT) (p less than 0.05; n = 4), whereas 3H-norepinephrine (NE) removal and 3H-benzoyl-phe-ala-pro (BPAP) substrate for lung angiotensin converting enzyme (ACE) metabolism in vivo, as well as lung and serum ACE activity in vitro remained at control levels. No morphologic or biochemical evidence of fibrosis was observed. In contrast, the high-dose BLM group exhibited significant reductions in 14C-5-HT and 3H-NE removal and 3H-BPAP metabolism in vivo, but no significant changes in lung or serum ACE activity in vitro. Furthermore, there was evidence of fibrosis, as revealed by a 59% increase in lung hydroxyproline content and by light microscopic examination of lung tissue. We conclude that intratracheal administration of BLM to rabbits can produce endothelial dysfunction in the presence or absence of interstitial injury.

Changes in angiotensin-converting enzyme activity in lungs damaged by the pyrrolizidine alkaloid monocrotaline.

Administration of monocrotaline, a pyrrolizidine alkaloid, to male Sprague-Dawley rats for up to three weeks increased dry lung weights by 64% and reduced the specific activity of lung angiotensin-converting enzyme activity by 64%. When the total activity per lung is calculated, however, there is no significant difference between control and monocrotaline-treated animals. The decrease in specific activity is due to increase in total lung protein (52% above control) and not to an actual reduction in the total angiotensin-converting enzyme activity in th lung.

Effect of acute oral administration of captopril and MK-421 on vascular angiotensis converting enzyme activity in the spontaneously hypertensive rat

Vascular angiotensin converting enzyme (ACE) may be important as a potential site of action for the antihypertensive effect of ACE inhibitors. ACE activity, estimated by hydrolysis of [ 3H] HipGlyGly, was similar in the aorta, mesenteric and carotid arteries of SHR. ACE activity in veins was not as consistent and was significantly lower in the jugular veins and vena cava of SHR than in the arteries. Nevertheless, ACE activity in all the blood vessels examined, although less than lung ACE activity, was higher than ACE activity found in other tissues such as brain, heart and kidney. Equieffective antihypertensive doses of captopril (10 mg/kg p.o.) and MK-421 (1.0 mg/kg p.o.) dramatically inhibited ACE activity in all the arteries and veins examined. Maximal ACE inhibition occured within 15 minutes after the oral administration of captopril. In contrast, maximal ACE inhibition was slower in onset and of longer duration after MK-421 than after captopril for all the vessels. Thus, relatively high ACE activity can be measured in both arteries and veins from the spontaneously hypertensive rat (SHR) and ACE was dramatically inhibited after antihypertensive oral doses of captopril or MK-421. Furthermore, vascular ACE inhibition can be used to compare the onset and duration of activity of ACE inhibitors; MK-421 has a longer onset and duration in SHR than captopril based on inhibition of ACE in blood vessels.

Lung angiotensin converting enzyme activity in rats with pulmonary hypertension.

We have studied serum and lung tissue angiotensin converting enzyme (ACE) activity in female Wistar rats with pulmonary hypertension induced by two different methods. Chronic pulmonary hypertension was produced in one group of 10 rats (CH) by confinement in a hypobaric chamber (380 mmHg) for three weeks, and in another group fo 10 rats (M) by a single subcutaneous injection of monocrotaline (60 mg/kg body weight). In these two groups of tests rats and in 20 untreated controls (C), we evaluated right ventricular mean systolic blood pressure (Prvs mmHg), right ventricular hypertrophy, and serum ACE (n mol/ml/min). In lung tissue homogenate, we measured the specific activity of ACE (n mol/mg protein/min), alkaline phosphatase (AP) (IU/mg protein) and lactic dehydrogenase (LDH) (IU/mg protein). The Prvs in groups, C, CH, and M was 25 +/- 7 SD, 41 +/- 7, and 51 +/- 5, respectively. The ratio of right ot left ventricular weight (RV/(LV + S)%) in groups, C, CH, and M was 29 +/- 4, 52 +/- 5, and 56 +/- 7, respectively. The lung tissue ACE in groups C, CH, and M was 85 +/- 11, 65 +/- 20, and 22 +/- 5, respectively. In groups CH, and M the Prvs and RV/(LV + S)% were significantly elevated above control values while lung ACE was significant decreased (p less than 0.05). There was a significant inverse relationship between lung ACE on one hand, and Prvs (r = - 0.73) and RV/(LV + S)% (r = - 0.71) on the other hand. Serum ACE and lung AP were unchanged. In group M there was a slight but significant reduction in lung LDH. Chronic pulmonary hypertension, irrespective of its method of production, is associated with decreased lung ACE. The reduction in lung ACE is inversely proportional to the severity of pulmonary hypertension and right ventricular hypertrophy.

Dissociation of the effect of captopril on blood pressure and angiotensin converting enzyme in serum and lungs of spontaneously hypertensive rats.

Spontaneously hypertensive rats (SHR) of the Okamoto-Aoki strain (n = 40) were treated with captopril (SQ 14,225; D-3-mercapto-2-methylpropanoyl-L-proline) orally, dose 0.2 mg/ml in drinking water. The treatment was initiated early and later during the course of developing hypertension. Continuously treated rats did not develop hypertension. Rats receiving captopril for 12 weeks remained normotensive, whereas withdrawal of the drug resulted in hypertension. Captopril treatment was effective in the rats with established hypertension and decreased the blood pressures to nearly normal values. Serum angiotensin converting enzyme (ACE) activity rose 3-fold in captopril treated rats. ACE in lung plasma membranes increased during captopril treatment, indicating that captopril induced biosynthesis of pulmonary ACE. No qualitative differences were found in the ACE from treated and not treated animals. The dissociation of the antihypertensive effect of captopril and of increased ACE activity in serum and lungs reduce the value of relating blood pressure effects of the drug to measured enzyme activity in the SHR.

Angiotensin converting enzyme activity in mice after subacute bleomycin administration

Multiple ip or sc injections of bleomycin (BLM) in mice elevated the serum and pulmonary activities of the peptidyl dipeptidase, angiotensin converting enzyme (ACE). ACE activity in lungs of mice treated every 3 days with BLM (9 mg/kg) was elevated 33, 36, and 45 days after the initiation of ip drug administration. After 12 BLM injections the increases in enzyme activities were dose related, with mice receiving the largest cumulative dose (108 mg/kg) having the greatest increase (53%) in lung ACE activity above control values. Mice treated every 3 days sc also had elevated pulmonary ACE activities after 15 injections, although liver and spleen activities were unaltered and the activities in the kidneys were reduced over 70% from control values. In addition to elevated lung ACE activity, serum ACE activity was increased 22 and 26% in mice treated ip and sc, respectively. A marked elevation in lung collagen as measured by lung hydroxyproline content was detected at the time of increased lung and serum ACE activity. Mice injected ip more frequently but with a lower dose of BLM (1.5 mg/kg, 2×/day, 5 days/week × 5 weeks) displayed no change in pulmonary ACE activity and hydroxyproline content even though they had received, over the same time period, a cumulative dose of BLM equal to that achieved by injecting 9 mg/kg of BLM every 3 days × 12. These data indicate that, subacute treatment of mice with BLM leads to an elevation in pulmonary and serum ACE activity and a decrease in renal ACE activity at the time of the development of fibrosis. The increase in lung ACE activity and hydroxyproline content appears to depend not only upon the total cumulative dose but also the dosage schedule. The elevation in serum ACE activity may reflect the loss of kidney enzyme or the shedding of pulmonary enzyme.

Biochemical and morphological assessments of bleomycin pulmonary toxicity in rats

Low doses (5 units) or high doses (15 units) of bleomycin were administered ip twice weekly to separate groups of male rats. A progressive dose-dependent reduction in body weight gain with a concomitant increase in wet lung weight to body weight ratio was observed over 6 weeks of treatments. Light microscopic confirmation of perivascular edema suggested that the increase in wet lung weight resulted from fluid accumulation. Although histological evidence of mild fibrosis was also present following low-dose treatment, only a slight increase in collagen content was observed biochemically. In vivo elevation of prolyl hydroxylase activity was observed in lungs of animals treated with low-dose bleomycin for 6 weeks. High-dose bleomycin regimen did not accelerate fibrosis, but rather inhibited the prolyl hydroxylase activity. In vitro, this enzyme activity was also stimulated at 1–10 μ m concentration, but was inhibited at 0.1 m m. Lung angiotensin-converting enzyme activity was examined as an indication of damage to endothelial cells. This activity was unchanged after low-dose bleomycin treatments until 6 weeks, at which time a 59% decrease in activity was observed. High-dose bleomycin treatment produced a biphasic response in angiotensin-converting enzyme activity, with an initial 32% stimulation after 1.5 weeks of treatment followed by a 41% inhibition after 3 weeks. Kinetic analysis of the in vitro interaction of purified porcine plasma angiotensin-converting enzyme with bleomycin indicated that bleomycin acts as a competitive inhibitor with a K i of 3.7 μ m. Stimulation of angiotensin-converting enzyme activity following acute high-dose bleomycin administration could be due to the initial endothelial cell repair, while the inhibition at later stages may indicate extensive destruction of endothelial surface upon repeated bleomycin administration. Direct inhibition of the enzyme by the chelating effect of bleomycin may also be a possibility.