Kern Wildenthal

A Longitudinal Study of Adaptive Changes in Oxygen Transport and Body Composition

The effects of a 20-day period of bed rest followed by a 55-day period of physical training were studied in five male subjects, aged 19 to 21. Three of the subjects had previously been sedentary, and two of them had been physically active. The studies after bed rest and after physical training were both compared with the initial control studies. Effects of Bed Rest All five subjects responded quite similarly to the bed rest period. The total body weight remained constant; however, lean body mass, total body water, intracellular fluid volume, red cell mass, and plasma volume tended to decrease. Electron microscopic studies of quadriceps muscle biopsies showed no significant changes. There was no effect on total lung capacity, forced vital capacity, one-second expiratory volume, alveolar-arterial oxygen tension difference, or membrane diffusing capacity for carbon monoxide. Total diffusing capacity and pulmonary capillary blood volume were slightly lower after bed rest. These changes were related to changes in pulmonary blood flow. Resting total heart volume decreased from 860 to 770 ml. The maximal oxygen uptake fell from 3.3 in the control study to 2.4 L/min after bed rest. Cardiac output, stroke volume, and arterial pressure at rest in supine and sitting positions did not change significantly. The cardiac output during supine exercise at 600 kpm/min decreased from 14.4 to 12.4 L/min, and stroke volume fell from 116 to 88 ml. Heart rate increased from 129 to 154 beats/min. There was no change in arterial pressure. Cardiac output during upright exercise at submaximal loads decreased approximately 15% and stroke volume 30%. Calculated heart rate at an oxygen uptake of 2 L/min increased from 145 to 180 beats/min. Mean arterial pressures were 10 to 20 mm Hg lower, but there was no change in total peripheral resistance. The A-V 02 difference was higher for any given level of oxygen uptake. Cardiac output during maximal work fell from 20.0 to 14.8 L/min and stroke volume from 104 to 74 ml. Total peripheral resistance and A-V 02 difference did not change. The Frank lead electrocardiogram showed reduced T-wave amplitude at rest and during submaximal exercise in both supine and upright position but no change during maximal work. The fall in maximal oxygen uptake was due to a reduction of stroke volume and cardiac output. The decrease cannot exclusively be attributed to an impairment of venous return during upright exercise. Stroke volume and cardiac output were reduced also during supine exercise. A direct effect on myocardial function, therefore, cannot be excluded. Effects of Physical Training In all five subjects physical training had no effect on lung volumes, timed vitalometry, and membrane diffusing capacity as compared with control values obtained before bed rest. Pulmonary capillary blood volume and total diffusing capacity were increased proportional to the increase in blood flow. Alveolar-arterial oxygen tension differences during exercise were smaller after training, suggesting an improved distribution of pulmonary blood flow with respect to ventilation. Red cell mass increased in the previously sedentary subjects from 1.93 to 2.05 L, and the two active subjects showed no change. Maximal oxygen uptake increased from a control value of 2.52 obtained before bed rest to 3.41 L/min after physical training in the three previously sedentary (+33%) and from 4.48 to 4.65 L/min in the two previously active subjects (+4%). Cardiac output and oxygen uptake during submaximal work did not change, but the heart rate was lower and the stroke volume higher for any given oxygen uptake after training in the sedentary group. In the sedentary subjects cardiac output during maximal work increased from 17.2 L/min in the control study before bed rest to 20.0 L/min after training (+16.5%). Arterio-venous oxygen difference increased from 14.6 to 17.0 ml/100 ml (+16.5%). Maximal heart rate remained constant, and stroke volume increased from 90 to 105 (+17%). Resting total heart volumes were 740 ml in the control study before bed rest and 812 ml after training. In the previously active subjects changes in heart volume, maximal cardiac output, stroke volume, and arteriovenous oxygen difference were less marked. Previous studies have shown increases of only 10 to 15% in the maximal oxygen uptake of young sedentary male subjects after training. The greater increase of 33% in maximal oxygen uptake in the present study was due equally to an increase in stroke volume and arteriovenous oxygen difference. These more marked changes may be attributed to a low initial level of maximal oxygen uptake and to an extremely strenuous and closely supervised training program.

Influence of starvation on the activities and localization of cathepsin D and other lysosomal enzymes in hearts of rabbits and mice.

An investigation was made in mice and rabbits of the effects of starvation on the activities and cellular localization of lysosomal enzymes in cardiac muscle of the left ventricle. The specific activity of cathepsin D was increased in the atrophying hearts of mice, by 14% after one day and by 26% after 3 days. Simultaneously, the proportion of the enzyme activity that was nonsedimentable during centrifugation at 40 000 g rose significantly, suggesting increased fragility of lysosomes or release of enzyme from lysosomes into the cytosol. In the same hearts protein concentration and the activities of acid phosphatase and beta-acetylglucosaminidase remained unchanged. Changes were similar in rabbit hearts except that specific cathepsin D activity was increased more (46%) and changes in the proportion of the activity that was nonsedimentable were less marked. Immunofluorescent staining for rabbit cathepsin D revealed that this acid proteinase was localized in lysosome-like particles in both interstitial cells and muscle fibres in hearts of normal animals. After 3 days starvation there was no detectable change in interstitial cells, but in the muscle fibres particulate staining was greater and, in addition, intense diffuse cytoplasmic staining was observed. The results indicate that cardiac muscle, like liver but unlike skeletal muscle, develops a significant increase in the activity of the lysosomal protease cathepsin D during starvation. The change occurs specifically in myocytes rather than in interstitial cells. The results suggest a possible role for cathepsin D in contributing to the development of cardiac atrophy and net protein catabolism during prolonged starvation.

Influence of Temperature on the Mechanical Properties of Cardiac Muscle

The influence of temperature on contractile performance, total myocardial stiffness, and the elastic and viscous components of stiffness was studied in intact hearts (dog) and isolated cardiac muscle (cat). In 12 dogs on whole-heart bypass, stiffness (ΔP/ΔV) was determined by inducing sinusoidal 0.5-ml volume changes in paced, isovolumically contracting left ventricles and measuring the resultant pressure changes (ΔP). In eight cat papillary muscles contracting isometrically at Lmax, stiffness (ΔT/ΔL) was similarly determined from the changes in tension and length during sinusoidal length changes of 0.25% L max. Total stiffness was linearly related to ventricular pressure or muscular tension during both contraction and rest. As the temperature rose from 33° to 40°C in vivo and from 22° to 40°C in vitro, the slopes of the stiffness-pressure and stiffness-tension relationships and the intercept of the latter declined; therefore, stiffness is inversely related to temperature. Since both preparations responded as linear second-order systems, stiffness could be separated into its elastic and viscous components. The moduli of both components varied in the same direction as total stiffness during temperature changes; however, the viscous component was more sensitive to the influence of temperature.

Effect on Left Ventricular Performance of Stimulation of an Afferent Nerve from Muscle

The effect on left ventricular performance of electrical stimulation of the cut central end of the quadriceps nerve was studied in open-chest dogs. Stimulation of the nerve at 2 to 4 times threshold for the flexion reflex, which presumably activated intermediate-sized afferent fibers, caused a decrease in heart rate and arterial pressure. Stimulation at 5 to 25 times threshold, which presumably activated small-sized, high-threshold afferent fibers, increased heart rate, arterial pressure, and cardiac output. When heart rate, arterial pressure, and cardiac output were controlled, activation of high-threshold afferent fibers caused a significant increase in the maximal rate of pressure rise, stroke power, and mean rate of ejection of the left ventricle without an increase in the end-diastolic pressure. These same fibers may in some way be activated during muscular exercise and be partially responsible for the increase in left ventricular contractility that occurs during that time.

Studies of foetal mouse hearts in organ culture: Metabolic requirements for prolonged function in nitro and the influence of cardiac maturation on substrate utilization

Abstract Isolated, intact hearts from foetal mice of 14 to 21 days gestational age survive and beat in organ culture for several days when the sole external substrate available for energy production is pyruvate, acetoacetate, β-hydroxybutyrate, octanoate, or glucose. Survival with glucose is significantly longer than with the other substrates. Inhibition of oxidative phosphorylation or of glycolysis causes early death of the hearts. Utilization of glucose is greater in hearts of younger (14 to 17 day) foetuses than in those of older foetuses near term (> 19 days gestation). Release of lactate is also greater in younger foetuses, both in absolute terms and as a proportion of the glucose consumed. The results suggest that long-term function in vitro of intact hearts of late-foetal mice requires the utilization of glucose as well as the oxidation of substrates through the tricarboxylic acid cycle. Glycolytic capacity assumes relatively less importance in cardiac metabolism as the foetus approaches term, but the availability of glucose remains essential for prolonged function.

Cardiac lysosomal derangements in mouse heart after long-term exposure to nonmetabolizable sugars.

SUMMARY Hearts of late fetal mice were maintained in organ culture in the presence of 30–100 mM sucrose or mannitol. Activities of several lysosomal enzymes (cathepsin D, β-acetylglucosaminidase, acid phosphatase) were increased by up to 30% after 18–24 hours and by up to 50% after 48–72 hours, as compared to enzyme activities in litter-matched hearts maintained in control medium or medium supplemented with equimolar urea. Simultaneously, the ratio of nonsedimentable to sedimentable enzyme activity was significantly increased, suggesting increased lysosomal fragility. Light and electron microscopic examination of the hearts revealed marked vacuolization in myocytic, interstitial, and endothelial cells. The vacuoles were limited by single membranes, often contained particulate or amorphous cellular debris resulting from autophagocytosis, and in cytochemical preparations frequently exhibited an electron-dense reaction product indicative of acid phosphatase activity. Hydrocortisone failed to prevent the marked lysosomal activation induced by the sugars. In conclusion, prolonged exposure to nonmetabolizable sugars induces severe lysosomal derangements with prominent autophagy, in fetal mouse heart maintained in organ culture.