SUMMARY yS-Amino proprionitrile (BAPN) at dietary concentrations of 1, 5, and 10 g BAPN/kg rat chow was administered to rats for 14-21 days following surgical constriction of the ascending aorta. Five and 10 g BAPN/kg rat chow prevented the increase in left ventricular collagen content which occurred with cardiac hypertrophy in rats following aortic constriction. In spite of this block in the increase in collagen in the ventricles, isolated trabecular muscles from hypertrophied hearts showed a decrease in maximum velocity of shortening at a preload of 0.5 g/mm 2 (max V) and an increase in time to peak tension as compared with values for sham-operated animals. Max V for rats with aortic constriction was decreased 0.57 muscle length/sec as compared with sham-operated animals (P< 0.01) whereas time to peak tension was prolonged by 12 msec (P < 0.05). In rats with aortic constriction receiving 10 g BAPN/kg rat chow, max V was decreased 0.66 muscle length/sec (P < 0.05), and time to peak tension was prolonged by 21 msec (P < 0.001). Resting tension was increased to 1.70 ± 0.18 (mean ± SEM) g/mm 2 as compared with shams (1.22 ± 0.10 g/mm 2 ; P < 0.002) in cardiac hypertrophy without BAPN. However, the increase in resting tension was not seen when animals with aortic constriction received 10 g BAPN/kg rat chow [1.23 ± 0.9 g/mm 2 as compared with shams, 1.15 ± 0.09 g/mm 2 (not significant)]. We conclude that the decrease in maximum velocity of shortening and prolongation of time to peak tension in experimental cardiac hypertrophy occur independently of elevated collagen content, whereas elevations in resting tension appear to depend upon an increase in collagen content of these hearts.IN THE past decade, numerous studies have attempted to characterize the mechanical performance of hypertrophied cardiac muscle. Several investigators 1 " 6 have reported a decrease in maximum shortening velocity of hypertrophied cardiac muscle when the hypertrophy was induced by a pressure overload. Whether the decrease in shortening velocity reflects a depression of cardiac "contractility" is a matter of controversy. 7 " 9 It seems clear, nonetheless, that an abnormality of cardiac performance follows acute experimental pressure overload. Additional mechanical changes have been described to accompany cardiac hypertrophy induced by pressure overload. These include a prolongation of contraction 2 ' 4l 6 and a change in passive compliance. 2 ' 5 In addition to the increase in RNA 10 ' n and protein synthesis, 12 ' 13 which accompanies experimental cardiac hypertrophy, enhanced thymidine incorportion into DNA has been demonstrated primarily in fibroblasts. 11 ' 14 ' lb Also, increased quantities of collagen are found in hypertrophied heart muscle. 2 ' 16 " 18 /?-amino proprionitrile (BAPN) is a lathyrogen which has been shown in vivo and in tissue culture to inhibit the cross-linking of collagen 19 ' 20 and elastin 21 probably by blocking the initial step in the enzymatic conversion of lysyl residues in peptide linkages to their aldehyde de...

Isolated, isovolumic rat hearts, perfused by Krebs-Henseleit buffer at constant coronary flow rate, were used to explore the hypothesis that endogenous cardiac glutathione provides protection against myocardial dysfunction associated with short periods of ischemia. Experimental animals were depleted of cardiac glutathione to 35% of control levels by intraperitoneal injections of diethylmaleate (DEM). Left ventricular pressure, coronary perfusion pressure, and glutathione levels were measured in control and experimental hearts after 60 minutes of oxygenated perfusion and after 20 minutes of global, no-flow ischemia and 30 minutes of reperfusion. With each protocol, both control and glutathione-depleted hearts received either standard buffer or one supplemented with 2 mM glutathione. Recovery of systolic function after ischemia-reperfusion was impaired in DEM-treated hearts compared with controls. In addition, the rise in perfusion pressure and chamber stiffness was also greater in DEM-treated hearts compared with controls. Recovery in glutathione-depleted hearts was improved when the reperfusate was supplemented with glutathione. In addition, the supplemented reperfusate prevented the decrease in compliance and the increase in coronary perfusion pressure in the glutathione-depleted hearts. Ischemia-reperfusion alone were not associated with a significant alteration in myocardial glutathione levels. Prewashout myocardial levels of glutathione were elevated after reperfusion with glutathione-supplemented bulfer but fell to baseline levels after a short washout period. These studies demonstrate that endogenous glutathione is important in protection of myocardium from injury after ischemia-reperfusion, presumably by modifying levels of active oxygen intermediates. The smaller changes in left ventricular pressure and coronary resistance after administration of GSH probably reflects an extracellular mechanism because benefit is seen soon after reperfusion. (Circulation 1989;80:1449-1457 D uring oxidative metabolism, cells produce potentially toxic oxygen radicals for which both specific and nonspecific scavenging mechanisms are present. Recently, it has been suggested that hypoxia or ischemia, followed by reoxygenation or reperfusion, increases production of oxygen radical species.1-5Administration of exogenous quenchers of free radicals, such as superoxide dismutase (SOD), catalase or both, improve cardiac function and limit infarct size when administered after experimental global ischemia.6,7From the Cardiology Section,

Diethylmaleate (DEM) decreases glutathione (GSH) levels in various organs by enzymatic conjugation with reduced GSH catalyzed by GSH transferase. We have examined levels of GSH, glutathione reductase (GR), and glucose-6-phosphate dehydrogenase (G6PD) in lungs of 200-250-g rats after intraperitoneal injection of 0.5 or 1 g DEM/kg body wt. The GSH levels are severely depressed at 2 and 4 h but have essentially recovered by 12 and 24 h after either dose of DEM. The GR and G6PD activities in the 1 g/kg group are depressed at 4 h to a lesser extent than the GSH levels and also return to normal by 12 and 24 h. These enzymes are not affected in the 0.5 g/kg group. To determine whether these transient decreases in GSH and related enzymes affected O2 tolerance, we exposed rats injected with DEM to greater than 98% O2 and found that halftime (t1/2) for survival was decreased in rats receiving both 0.5 and 1 g DEM/kg body wt when compared with untreated or saline-injected controls (t1/2 control, 74 h; 0.5 g DEM, 59 h; 1 g DEM, 53 h). No deaths occurred in air controls at 1 mg/kg DEM for up to 5 days. DEM, in itself, caused no morphological alteration of the lung. Thus a decrease in lung GSH and related enzymes, occurring by 4 h and reversed by 12 h, has a significant effect on the subsequent progression of lung pathology and indicates that early biochemical events occurring in lungs exposed to hyperoxia may be very important in determining the degree of longer-term damage to rat lungs.

Rats fed 3% casein diets for 6 days showed an increased susceptibility to greater than 98% oxygen [mean survival time 46.9 +/- 4.1 (SD) h] compared with animals fed 25% casein diets (mean survival time 60 +/- 5 h). The 3% casein diet did not reduce the responses to hyperoxia of lung glucose-6-phosphate dehydrogenase, glutathione peroxidase, and glutathione reductase (NAD(P)H), which maintain tissue levels of reduced glutathione or lung superoxide dismutase levels. While supplementation of the 3% casein diet with the sulfur-containing amino acids (cysteine, cystine, or methionine) prevented the increased oxygen toxicity, supplementation with leucine, a nonsulfur-containing amino acid, had no effect on potentiation of toxicity. Animals fed the unsupplemented 3% casein diet failed to show an elevation of lung glutathione in response to hyperoxia. When the 3% casein diet was supplemented with cysteine, total lung glutathione levels increased normally during oxygen exposure. Supplementation of the 25% protein diet with cysteine did not further protect these animals. We conclude that potentiation of oxygen toxicity by dietary protein deficiency in the rat is due to the low sulfur-containing amino acid content of the diet; the mechanism of increased toxicity by hyperoxia is probably related to an inability to increase glutathione levels due to a shortage of the cysteine component of the glutathione tripeptide.

Intracellular glutathione was increased by 80% after exposure of bovine pulmonary arterial endothelial cells to 80% O2 (hyperoxia) for 24 h. No change in glutathione occurred in cells exposed to hypoxia (3% O2) for a corresponding period of time. The rate of uptake of [3H]glutamic acid also increased by 35-55% after 24 h of exposure of cells to hyperoxia, whereas exposure to hypoxia had no effect on the [3H]glutamic acid uptake. The increase in glutamic acid uptake reflected a specific effect on amino acid transport systems rather than a change in cell membrane permeability. The major portion of the increased uptake was inhibited by the elimination of sodium and the addition of the competitive inhibitor, cystine, to the incubation medium. Thus increases in glutamic acid uptake parallel increases in cellular glutathione, and glutamic acid may be a regulating factor in the increase in glutathione after exposure to hyperoxia.

The angiotensin I converting enzyme was purified 101 000-fold to homogeneity from human plasma by a combination of chromatographic and electrophoretic techniques. The enzyme is similar to other angiotensin I converting enzymes. It is an acidic glycoprotein consisting of a single polypeptide chain of molecular weight 140 000 with an isoelectric point of 4.6. The enzyme requires chloride ion for activity and is inhibited by ethylenediaminetetraacetic acid, angiotensin II, bradykinin, bradykinin potentiating factor nonapeptide, and 3-mercapto-2-D-methylpropanoyl-L-proline (SQ-14,225). The purified preparation cleaves bradykinin as well as angiotensin II and hippuryl-L-histidyl-L-leucine. Its specific activity with angiotensin I is 2.4 units per mg and with hippuryl-L-histidyl-L-leucine is 31.4 units per mg.

Oxygen-derived free radicals (OFR) have been implicated as mediators of tissue injury in various disease states. Their participation in myocardial injury due to ischemia-reperfusion has also been suggested. To characterize the mechanical dysfunction associated with OFR-induced injury, we studied alterations in isometric contractions of rat papillary muscle at 28 degrees C. A purine-xanthine oxidase system was used to generate OFR. Neither purine nor xanthine oxidase alone had significant effects on rest or active tension, duration of the contraction, or peak rates of tension development or decline. In contrast, their combination resulted in a reduction of active tension to 38% of base-line values without alteration in rest tension. This reduction was largely due to a decline in the peak rate of tension development. When catalase or superoxide dismutase was introduced into the bath prior to the generation of OFR, catalase but not superoxide dismutase offered essentially complete functional protection. These results substantiate that impaired myocardial function can result from exposure to OFR. In this case the active radicals appear to be either peroxides or hydroxyl and not superoxide. These observations provide a basis for understanding the functional protection afforded ischemic myocardium by OFR scavenging enzymes.

Chemo-irradiation induced oxidative damage to vascular endothelium may contribute to pulmonary complications of hematopoietic stem cell transplantation (HSCT). We measured antioxidants, markers of oxidative stress and plasma antioxidant capacity in plasma or serum from 24 subjects at day 7 before HSCT and 20 control subjects. The plasma concentration of extracellular glutathione peroxidase (GPX-3) was significantly reduced in the HSCT subjects compared with controls (HSCT: 98742 lg/ml, control: 169756 lg/ml, Po0.0001). The concentration of c-tocopherol was significantly higher in the HSCT subjects compared with controls (HSCT: 2077103 lg/dl; Control: 98752 lg/dl; P ¼ 0.0002). The plasma concentrations of protein carbonyl, nitrotyrosine, malondialdehyde, a-tocopherol, vitamin A, homocysteine, cysteine and cysteinylglycine did not differ between HSCT and control subjects. Plasma from HSCT subjects was as effective as control plasma in quenching menadione-induced intracellular reactive oxygen species production in human microvascular endothelial cells. In summary, subjects before HSCT have significantly reduced plasma concentrations of GPX-3, elevated plasma c-tocopherol yet retains the ability to quench an acute oxidative stress. These changes may play a role in chronic oxidative stress in the HSCT population.