Kathleen H. McDonough

Exercise Training Improves Cardiac Performance in Diabetic Rats

Abstract Diabetes mellitus is often associated with a cardiomyopathy characterized by alterations in cardiac metabolism and declines in cardiac performance. We sought to determine whether exercise training would attenuate the depressed cardiac performance seen in diabetic animals. Female rats were divided into four groups: sedentary control, trained control, sedentary diabetics, and trained diabetics. After 1 week of training, we induced diabetes by intravenous injection of streptozotocin (65 mg/kg). We trained animals on a treadmill using a progressive protocol that plateaued at 27 m/min for 1 hr/day, 5 days/week for a total of 8 weeks. We measured cardiac output at a variety of left atrial filling pressures with an isolated working heart apparatus; glucose was the sole metabolic substrate for the heart. Training increased succinate dehydrogenase activity in the soleus muscle of exercised rats, but did not change heart and body weights or plasma glucose and thyroid hormone levels. The diabetic groups exhibited depressed cardiac outputs at high workloads compared to nondiabetics. Training increased the cardiac output of both sedentary and diabetic animals at high, but not low, preloads. We suggest that exercise can attenuate the severity of diabetic cardiomyopathy. [P.S.E.B.M. 1993, Vol 203]

Effect of chronic alcohol consumption by rats on tumor necrosis factor-α and interleukin-6 clearance in vivo and by the isolated, perfused liver☆

The effects of chronic (16-week) alcohol consumption by rats on [125I]tumor necrosis factor (TNF)-α and [125I]interleukin (IL)-6 plasma clearance and organ distribution in vivo and uptake and metabolism by the isolated, perfused liver were studied. Alcohol was administered to rats in a liquid diet for 16 weeks, and caused a decreased (48%) plasma clearance rate of IL-6 and converted the plasma clearance kinetics of the cytokine from a biphasic exponential in normal rats to a monophasic exponential decay. Alcohol feeding significantly increased (101%) plasma clearance of TNF-α, which followed a biphasic exponential decay and decreased the T12 for both the α (67%) and β (76%) elimination components. The distribution of both cytokines in trichloroacetic acid precipitable and non-precipitable fractions of liver, spleen, stomach, small intestine (ileum), lung, kidney, and blood was also studied. The only effect of alcohol treatment was a significant decrease in IL-6 uptake and metabolism by the small intestine. Perfused livers, isolated from alcohol-fed rats, took up and metabolized larger amounts of IL-6 than did livers isolated from pair-fed rats. TNF-α uptake and metabolism by the isolated, perfused liver were not affected by chronic alcohol consumption. Regardless of the animal treatment, the isolated perfused liver took up and metabolized significantly larger (17-fold) amounts of TNF-α than IL-6, in spite of identical concentrations of cytokines (6 nM) in the perfusion medium. The data presented in this study along with our previous results demonstrating the effects of alcohol consumption on TNF-α and IL-6 receptors on various liver cells suggest that the effects of chronic alcohol treatment on cytokine clearance cannot be ascribed to changes in the receptors for the two cytokines. Also, no correlation was found between the effects of alcohol treatment on plasma cytokine clearance and uptake and metabolism of cytokines by the isolated, perfused liver. Experimental data and theoretical considerations suggest that cytokine receptor recycling may play an important role in mediating alcohol effects on cytokine clearance.

The effect of acute ethanol exposure on the chronotropic and inotropic function of the rat right atrium.

Consumption of ethanol (CH2CH3OH), both acutely and chronically, is known to affect cardiac function and may alter the autonomic control of the heart. This study investigated the effects of two modes of acute exposure to ethanol on the chronotropy and inotropy of the rat right atrium with emphasis on alterations in the adrenergic responses.

Effects of oxygen radicals on substrate oxidation by cardiac myocytes

Freshly isolated adult rat heart cells were used to study the effects of oxygen-free radicals on the myocardial oxidation of different substrates. The calcium-tolerant quiescent cells were incubated with xanthine plus xanthine oxidase as the source of free radicals. The oxidation of exogenous glucose, lactate and octanoate was severely inhibited (approx. 70%) by products of xanthine oxidase activity. Superoxide dismutase plus catalase effectively prevented the inhibition of oxidation. Cellular high energy phosphate levels were decreased in the presence of the oxygen free radical generating system although cell viability determined by Trypan blue exclusion and light microscopic assessment of normal morphology was not affected. These data suggest that oxygen free radicals decrease myocardial substrate oxidation which may contribute to the functional and ultrastructural changes in the myocardium under conditions such as reoxygenation after hypoxia and reperfusion after ischemia.

Effects of Hypoxia and Reoxygenation on Adult Rat Heart Cell Metabolism

Abstract Isolated adult rat heart cells were used to study the effects of oxygen deprivation followed by reoxygenation upon myocardial metabolism. Calcium-tolerant nonbeating myocytes were incubated for 5, 30, or 60 min under 100% oxygen or 100% nitrogen and then rinsed with oxygenated buffer. Substrate oxidation was studied by incubating the cells with 14C-labeled glucose, pyruvate, or octanoate and determining the rates of 14CO2 production from the individual substrates. After 5 min of hypoxia, metabolism of glucose, as assessed by glucose oxidation and lactate production, was significantly depressed. Pyruvate and octanoate oxidation were unaltered. Oxygen consumption was also unchanged by short-term hypoxia and reoxygenation. With reoxygenation after 30 min of oxygen deprivation, more exaggerated changes in glucose metabolism were noted as well as a depression in pyruvate oxidation and unaltered octanoate oxidation. Oxidation of octanoate was slightly depressed after 60 min of hypoxia. Cell viability assessed after reoxygenation was not significantly altered until 60 min of oxygen deprivation. The results indicate that cytosolic changes occur after short periods of hypoxia followed by reoxygenation, whereas mitochondrial function is more resistant to damage inflicted by hypoxia and reoxygenation.

The Right Ventricular Working Heart Preparation

Abstract An isolated working rat heart preparation was modified to study right ventricular (RV) performance. All hearts were perfused with a Krebs-Henseleit bicarbonate buffer via a Langendorff column at 90 mm Hg. Right atrial filling (preload) was varied by raising a buffer reservoir from 5 cm below to 10 cm above the right atrium while pulmonary artery outflow resistance remained fixed. RV systolic pressure and the maximum rise and decrease in pressure development (±dP/dt) were measured via a catheter in the RV. Cardiac output was collected with a catheter placed in the pulmonary artery. One group of hearts, monitored at a fixed preload (0 cm H2O) for 2 hr, and another group of hearts, in which two ventricular function curves were performed, demonstrated the stability and reproducibility of the preparation. Additionally, the ability of this preparation to measure changes in inotropy was studied. A negative inotropic effect was measured after verapamil (5 × 10-8 M) treatment. Positive dP/dt showed the greatest depression (30%) and was significantly lower at every preload. A positive inotropic effect was demonstrated by reducing the buffer Ca2+ concentration to 1.9 mM for the first work curve followed by an addition of Ca2+ (2.8 mM final concentration) or ouabain (5 × 10-5 M) for the second work curve. Again, the greatest effect was found in the dP/dt measurements (elevated by 20 and 30%, respectively). Thus, this preparation manifests qualities similar to those used in studying the left ventricle and allows investigation of various cardiac diseases which may affect RV pump function.

Effect of essential fatty acid deficiency on forskolin binding sites, adenylate cyclase and cyclic AMP-dependent protein kinase activity, the levels of G proteins and ventricular function in rat heart

Three groups of rats were fed semi-purified diets. Diet I was deficient in essential fatty acids (EFAD), diet II was marginally deficient in essential fatty acids (MEFAD), and diet III contained adequate levels of essential fatty acids (control). After 9 weeks, some rats within each group were killed and cardiac membranes were prepared. Adenylate cyclase activity, [3H]forskolin binding sites, the levels of G proteins (Gi and Gs) and fatty acid composition of the membrane phospholipids were measured. Typical changes of EFA deficiency were observed in fatty acid composition of the membrane phospholipids. Adenylate cyclase activity was significantly lower in membranes of EFA-deficient rats than those of the controls. The MEFAD group gave intermediate values. Similar results were obtained with forskolin-stimulated activity with different concentrations of forskolin. Concentrations of the forskolin binding sites were also lower in the EFAD, but not in the MEFAD rats compared with the controls. There was no significant difference in forskolin binding affinities among the three groups. The decrease in adenylate cyclase activity in EFA-deficient rat heart was partially restored by feeding the control diet for 5 weeks to the EFAD or the MEFAD rats. The levels of Gi alpha and Gs alpha were not significantly different in cardiac membranes of rats fed the EFAD or the MEFAD diets from those of the control group. Lower adenylate cyclase activity in hearts of EFAD rats was also reflected in correspondingly lower activity of cAMP-dependent protein kinase. The results suggest an impairment of the cellular signalling pathway for the production of cAMP in rat heart during EFA deficiency. The beta-adrenergic response of isolated heart preparations obtained from rats fed the three diets was, however, not significantly altered.