Synthesis and degradation of mitochondrial components in hypertrophied rat heart

The accumulation of inner mitochondrial components of rat heart was studied 1 and 3 days after constriction of the ascending aorta of rats. By 1 day after aortic constriction, the activities of three mitochondrial respiratory enzymes/mg of cardiac homogenate protein were increased; after 3 days, specific activities had levelled off or decreased. Selective accumulation of inner mitochondrial membrane components 24h after aortic constriction was further indicated by increased left ventricular cytochrome c concentration (nmol/mg of protein). By 3 days after surgery, cytochrome c concentration was significantly diminished. Low-temperature spectroscopy of isolated mitochondria showed that the ratios of cytochromes c, b and a+a(3) remained unchanged after aortic constriction, suggesting that cytochrome c was a good indicator of the response of the other mitochondrial inner-membrane cytochromes as well. The effect of cardiac hypertrophy on the turnover of cytochrome c was also examined. Cytochrome c was labelled in its haem group with delta-amino[2,3-(3)H(2)]laevulinate 3 days before aortic constriction. By 1 day after surgery the total ventricular radioactivity in cytochrome c of aortic banded animals was significantly higher than in sham-operated controls, indicating a decreased degradation rate in the former during the first postoperative day. delta-Aminolaevulinate was shown to be a particularly suitable precursor for such turnover studies, since it results in rapid pulse-labelling of cytochrome c (peak activity in 90min), is rapidly removed from the precursor pool (t((1/2))=30min) and is not reutilized.

Biochemical "defect" in the hypertrophied and failing heart: deleterious or compensatory?

"It is generally established that the normal heart may become incapable of maintaining an adequate cardiac output or preventing venous engorgement whenever it is presented acutely with an overwhelming load beyond its pumping capacity. This state is not failure of a diseased heart, but it has been designated `failure' by many. It is more difficult to define the situation where such an overload sets up a vicious cycle which progressively potentiates the load upon the heart for hours or days. After a lapse of time, this load strains the mechanisms available for compensation to the point where venous congestion or reduced cardiac output becomes evident. Does this turning point mean that the heart has become abnormal, in a functional sense, and, therefore, is it now to be a case of heart failure in the accepted sense? . . . How much of the circulatory change is due to the load and how much to mechanisms called upon to meet the load? When does myocardial deterioration begin, and when does myocardial failure start? . . . How can one determine whether it is cardiac loading or myocardial failure whch is responsible for invoking the compensatory mechanisms?" 1

Triglycerides, cholesterol, and phospholipids in normal heart papillary muscle and in patients suffering from diabetes, cholelithiasis, hypertension, and coronary atheroma

The triglyceride, cholesterol, and phospholipid contents of heart papillary muscle were measured in groups of obviously healthy and diseased females and males on whom either routine or forensic necropsies were performed. In healthy men the triglyceride content was 1.77 +/- 1.30 mg/g of wet weight and in women 1.25 +/- 0.48 mg/g wet weight. The corresponding values for cholesterol were 1.07 +/- 0.24 mg/g and 1.21 +/- 0.22 mg/g and those for phospholipids 17.70 +/- 5.15 mg/g and 19.65 +/- 10.21 mg/g. The differences between the sexes were not significant. The hypertensive or cardiac hypertrophy group had about the same or slightly lower means for lipid content. In the cholelithiasis group, women had significantly high triglyceride values (3.38 +/- 2.36 mg/g). The cholesterol values were not significantly elevated in either men or women. In the diabetic group, triglycerides were significantly increased both in men (mean 8.12 +/- 0.54 mg/g) and in women (6.85 +/- 5.66 mg/g). The cholesterol mean values were also high in both sexes, but the rise was not significant because of the great variation. In the coronary atheroma group, both male and female hospital cases had high triglyceride contents (mean 4.48 +/- 4.25 mg/g and 3.65 +/- 3.94 mg/g) whereas the forensic cases had only slightly elevated or normal values. Cholesterol assays paralleled the triglyceride ones, but phospholipids showed an inverse trend. The results showed that the lipid content of papillary muscle was increased in diseases where disturbances of lipid metabolism are evident, as in diabetes and cholelithiasis. In coronary atheroma only those cases with advanced obstruction of the arteries were associated with abnormal values of papillary lipids. No increase of the lipid content with age alone was found, nor was there any correlation with obesity.

Effect of long-term physical stress on collagen growth in the lung, heart, and femur of young and adult rats

Male Wistar rats, 1.8 and 7.5 months old, were adapted to exercise on the treadmill for a period of 7 weeks. The animals were trained 3 h daily at the treadmill speed of 24 m/min. Wet and dry weights and collagenous hydroxyl-proline content in the lung, heart, and femur were analyzed. Physical stress did not affect any of the parameters studied in the lung. Cardiomegaly developed only in the young rats exposed to training. There was significantly higher total amount and density of collagen in the hyper-trophic heart. In contrast to the reactivity of the heart to physical stress, the amount and density of collagen in the femora was significantly increased only in the adult rats. There was no effect on the content of calcium in the bone. The calcium-collagen ratio was, therefore, significantly lower in the trained rats. It is concluded that collagen in every organ reacts differently to physical stress in relation to age.

Functions of cells and biosynthesis of protein in aging

The relationship between cell function and protein biosynthesis undergoes a change in aging. In old animals a continuous stress in the action of cells in a smaller degree activates the protein biosynthesis system; the activity of their genetic apparatus is easier to suppress or inhibit. A new and important molecular mechanism of applying the cell function in aging has been demonstrated shifts in protein biosynthesis have an effect on hyperpolarization of cellular membranes, and this leads to a change in cell function through aging.

Biochemical correlates of cardiac hypertrophy. V. Labeling of collagen, myosin, and nuclear DNA during experimental myocardial hypertrophy in the rat

The incorporation of [2, 3- 3 H]proline into collagen hydroxyproline and into noncollagenous protein was measured during development of cardiac hypertrophy produced by surgical constriction of the ascending aorta in rats. Heart weight increased sharply during the first 4 days after aortic banding and then slowly rose to a plateau. Free intracellular proline concentration remained unaltered 2 days after banding and increased by 38% on the fifth postoperative day. Specific radioactivity of free proline 3 hours after injection of [ 3 H]proline was elevated by 40% on the second postoperative day but was unchanged on the fifth day. Incorporation of [ 3 H]proline into collagen hydroxyproline peaked sharply on the second day after aortic constriction (550% above control) in one experiment, and on the fourth day (330% above control) in another. The peak labeling of noncollagenous protein by [ 3 H]proline (100% over control) was less than that of collagen. To further evaluate the differences in synthetic response of muscle cells and interstitial cells to increased work load, incorporation of radioactive precursors into myosin, collagen, nuclear DNA, and noncollagenous protein were measured simultaneously, after aortic constriction. Collagen labeling was maximal either on day 2 or 4, depending on the degree of hypertrophy. Labeling of myosin and noncollagenous protein reached a plateau on day 4. Incorporation of [ 3 H]thymidine into nuclear DNA peaked on day 7. Thus both muscle cells and connective tissue cells respond independently during cardiac hypertrophy with an increased synthesis of specific proteins.

Myosin synthesis and degradation during development of cardiac hypertrophy in the rabbit

Metabolism of left ventricular myosin was studied in rabbits (2.7-3.2 kg) following banding of the ascending aorta (65% occlusion). In 26 rabbits the incorporation of amino acid into myosin was determined 2, 3, 4, 9, and 15 days after either stenosis or sham operation by injecting 3 H-lysine (0.5 mc/kg) 4 hours before the animals were killed. In 32 rabbits the same dose of 3 H-lysine was injected 24 hours before surgery, and disappearance of isotope from myosin was measured by killing the rabbits after 3, 5, 7, 10, or 16 days. Specific radioactivity of free lysine, myosin, and total proteins was determined in left ventricular samples from each animal. The experimental results indicate that: (1) left ventricular peak systolic pressure increased from 97 to 163 mm Hg; (2) the ratio of left ventricular weight to body weight increased about 16% (3) disappearance of free 3 H-lysine was similar in rabbits with aortic stenosis and those with sham operations; (4) after the second day myosin synthesis was greater in rabbits with aortic coarctations, reaching a maximum increase of 117% on the tenth day; (5) synthesis of left ventricular total proteins also reached a maximum of about 56% on the tenth day; (6) the decrease in specific radioactivity of myosin in rabbits with aortic coarctation was slower than it was in sham-operated animals. The experimental results were analyzed by a computerized simulation of myosin metabolism which allowed the rate constant for myosin degradation to be calculated on successive days after coarctation. The best fit to the observed changes in myosin content was obtained when degradation was increased with the increase in synthesis; when degradation was assumed to be unchanged from sham-operated animals or was decreased, myosin content was overestimated. Moreover, these calculations showed that decay in specific radioactivity of labeled myosin was affected very little even by a large (hundredfold) decrease in degradation. It is concluded that the increased myosin content during development of cardiac hypertrophy is primarily a consequence of increased synthesis.