The effects of experimental coronary atherosclerosis on myocardial high energy phosphates and regional coronary perfusion and oxygen delivery were studied. Hypercholesterolemic (HC) New Zealand white rabbits developed mild to moderate coronary vascular disease in 4 months when serum cholesterol levels were maintained at 1500--2000 mg/dl. Resting left ventricular levels of creatine phosphate, adenosine triphosphate (ATP), and the cellular energy charge were unaltered after 2 months of diet but were decreased after 4 and 6 months. Tissue lactate and the lactate/pyruvate ratio were increased after 4 months, suggesting mild tissue ischemia. The regional blood flow rate was measured in rabbits given pentobarbital after 6 months of diet using labeled microspheres, and the response to stress was tested after 5 minutes of hypoxic ventilation (5% O2/N2). The percentage of cardiac output to subendocardium (endo) and subepicardium (epi) in HC rabbits and that in control animals were similar at rest, but unlike that of control animals, the endo perfusion did not increase significantly in HC animals during hypoxic stress. Baseline regional left ventricular oxygen deliveries were similar between groups, but the baseline endo/epi oxygen delivery ratio was reduced in HC rabbits. In control rabbits hypoxia did not alter total O2 delivery, and the endo/epi oxygen delivery ratio was constant, whereas hypoxia in HC animals produced a decrease in total oxygen delivery and a further decrease in the endo/epi oxygen delivery ratio. Thus, moderate long-term coronary occlusive disease produced alterations in the distribution of coronary perfusion that are similar to those after acute partial occlusion, ie, selective reductions in blood flow and oxygen delivery to subendocardium. These results may relate to the pathogenesis of subendocardial infarction in man, which often occurs in the absence of complete coronary occlusion.

The rate of ATP supported Ca2 uptake by mitochondria isolated from normal swine aorta was found to be influenced by Ca2+, ATP, protein and H+ concentrations. Vmax was not reached even at 273 μM, the highest [Ca+] tested. Initial rate of uptake at this concentration was 1200 nmoles/min/mg and maximal uptake was 1400 nmoles/mg. At a mitochondrial protein concentration of 90 μg/ml and 118 μM Ca2+, the pH optimum for uptake was 7.5 and optimal ATP was 1.2-2.3 mM.

Aspects of myocardial oxidative phosphorylation and Ca2+ metabolism were studied in a swine model in which coronary atherosclerosis was induced by a combination of denudation of the endothelium of the coronary arteries plus 7--11 months of feeding a high fat--high cholesterol diet. By microscopy, a moderate amount of coronary atherosclerosis was present at the time of sacrifice, and 2 of the 14 swine hearts had old myocardial infarcts. Myocardial mitochondria from grossly normal areas showed partial uncoupling and decreased state 3 O2 uptake with 3 of 4 substrates tested. In addition, Ca2+ stimulated mitochondrial respiration was decreased in the atherosclerotic swine. In the sarcoplasmic reticulum Ca2+ uptake under conditions of heavy loading was greater in the atherosclerotic swine than in control animals. The degree of atherosclerosis was not great enough to suggest that persistent myocardial ischaemia was present. Possibly coronary artery spasm induced an intermittent ischaemia resulting in the metabolic abnormalities observed, or the changes may have been brought about by the effects of the high fat--high cholesterol diet on subcellular membranes.

The effect of methyl prednisolone and colchicine on the development of both the early proliferative and advanced atherosclerotic lesion in swine aorta was studied. In order to accelerate the development of atherosclerosis, the abdominal aortic endothelium was partially denuded by a balloon before the animals were placed on either a moderate or severe hypercholesterolemic diet. Neither drug in either dietary group inhibited the development of atherosclerosis. Swine receiving methyl prednisolone and severe hypercholesterolemic diet actually had a significantly greater number of the advanced necrotic lesions and more arterial calcification than the group receiving the atherogenic diet alone. In addition, the thoracic aorta of swine receiving the moderate hypercholesterolemic diet and methyl prednisolone showed larger amounts of lipid than did the non-drug fed control group. In swine receiving the moderate hypercholesterolemic diet, methyl prednisolone significantly raised serum cholesterol levels. Colchicine only slightly worsened the atherosclerosis in swine aorta and had no effect on serum cholesterol levels.

Hepatic mitochondria of swine fed ethylchlorophenoxyisobutyrate (CPIB) at a level of 0.3% (w/w) for 8 weeks showed partial uncoupling of oxidative phosphorylation and increased state 4 QO2 values. Both cytochrome oxidase and the calculated theoretical mitochondrial protein were increased per gram of total liver. Whether related or not these changes were accompanied by the appearance of tubular spiral structures within the mitochondria. Swine fed CPIB for 4 weeks showed similar but fewer functional and morphologic changes. Feeding the drug 1 week produced no abnormalities of oxidative phosphorylation or QO2 values, and no morphologic changes were present. However, at this time calculated theoretical mitochondrial protein, cytochrome oxidase, and monoamine oxidase activities were already increased per unit of liver weight.

Intimamedia tissue from atherosclerotic rabbits showed a 15-fold increase in the amount of [U-14C]palmitic acid oxidized to CO2 compared to normal intimamedia. The findings suggest that oxidation of free fatty acids may at least in part contribute to the increased oxygen uptake seen in atherosclerotic tissue. The concentration of endogenous free fatty acids in atherosclerotic tissue was much higher than in normal tissue. The higher level may have been partly due to the increased levels of serum free fatty acid in the atherosclerotic rabbits, and to the increased permeability of atherosclerotic intimamedia to free fatty acids demonstrated in vitro. The tissue from atherosclerotic rabbit aortas exhibited a different pattern of fatty acid esterification than did that obtained from control aortas. In atherosclerotic tissue more cholesterol ester than triglyceride was formed from palmitate. In determining the specific activity of the free fatty acid tissue pool(s), equilibration of medium and tissue free fatty acid was found to be slow. In addition, the amount of free fatty acid in aorta was substantial and somewhat variable from animal to animal. Therefore, it was necessary to base calculations of fatty acid metabolic pathways on the specific activity of the palmitate in the tissue and not on that of the medium.

An improved method for isolating aortic mitochondria with good respiratory control has been developed. Using this method, mitochondria were isolated from atherosclerotic and normal aortic intima-media tissue in both swine and rabbits. No differences could be found in State 3 O 2 uptake, acceptor control ratios or ADP O ratios in mitochondria from the atherosclerotic vs normal tissue in either species. The study suggests that mitochondrial function in the proliferative (non-necrotic) phase of atherosclerosis is not impaired.

High energy compounds (adenosine triphosphate and creatine phosphate), lactate and mitochondrial function and morphology were investigated in swine suffering from persistent myocardial ischemia. The myocardial ischemia was secondary to severe diffuse coronary artery atherosclerosis induced by hypercholesterolemia enhanced by X-irradiation to the heart.