ber das Verh�ltnis Mitochondrien: Myofibrillen in den Herzmuskelzellen der Ratte bei Druckhypertrophie des Herzens

Low-dosage statins reduce choroidal damage in hypercholesterolemic rabbits

PURPOSE

To describe the ultrastructural changes in the choroid of long-term hypercholesterolemic rabbits after a low-dosage statin treatment and to evaluate some pleiotropic effects of these drugs on the morphology of endothelial cells (EC) and vascular smooth-muscle cells (VSMC).

METHODS

New Zealand rabbits were divided into three groups: G0, fed a standard diet; G1, fed a 0.5% cholesterol-enriched diet for 8 months and G2, fed a 0.5% cholesterol-enriched diet for 8 months plus administration of fluvastatin sodium or pravastatin sodium at a dose of 2 mg/Kg/day each. Eyes were processed for transmission-electron microscopy.

RESULTS

G1 had a lipid build-up at the suprachoroidea that compressed the vascular layers with the lumens of the vessels to the point of collapse in some instances. By contrast, G2 underwent a substantial decrease in suprachoroidal foam cells and of lipids in the vascular layers while the vascular lumens were normal. The preservation of cytoplasmic organelles, caveolar system and other ultrastructural features of EC and VSMC in G2 contrasted with the numerous signs of necrosis observed in G1. Bruch's membrane (BM) in G2 contained fewer lipids and more collagen than in G1.

CONCLUSION

Treatment with a low dosage of fluvastatin sodium or pravastatin sodium reduced the lipid build-up as well as the macrophages in the choroid and restored the vascular lumens of choroidal vessels independently of the cholesterol effect. The normal ultrastructural features of choroidal EC and VSMC in statin-treated animals suggest that the endothelial function is preserved and the ischaemia reduced.

Pravastatin protection from cold stress in myocardium of rats

The aim of this research was to evaluate the possible protective effect of pravastatin on ultrastructural alterations induced by cold stress in the myocardium of rats. Sixteen EPM-Wistar rats (Rattus norvegicus albinus) were used and distributed into four groups: 1) control; 2) pravastatin; 3) cold stress, and 4) pravastatin + cold stress. A daily oral dose of 10 mg/kg of weight of pravastatin was administered to each rat in groups 2 and 4 for 15 days. The stress induced by cold was obtained by keeping the group 3 and 4 rats in a freezer at -8 degrees C for 4 hours. The animals were killed and the heart and fragments of the left ventricles (LV) were removed and processed prior to conducting electron microscopic analysis. The ultrastructural alterations in cardiomyocytes were quantified through the number of mitochondrial cristae pattern (cristalysis). The group subjected only to cold stress showed a significant increase in cristalysis (391.9) when compared with control group (42.0). In the cold stress and pravastatin pretreatment group, a statistically significant (96.9)*, P<0.05 cristalysis reduction was observed when compared with cold stress group. The mitochondrial cristalysis profiles of the control and pravastatin groups were 42.0 and 65.7, respectively. Cold stress induced a significant increase in the rate of mitochondrial cristalysis. In the group that received pravastatin and was exposed to cold stress, the drug protected the LV cardiomyocytes. This fact was confirmed by a reduction mitochondrial cristalysis pattern.

Pressure induced hypertrophy in the hearts of growing dwarf pigs

The left ventricles of 8 sibling dwarf pigs were stressed by banding the aorta ascendens for 7 to 49 days. There was no developmental retardation. Neither light nor electron microscopic controls showed signs of insufficiency. 3.7 X 10(7) Bq/kg (1 mCi/kg) body weight (3 H-)methyl thymidine had been applied as pulse at the end of the experiment. The 3 H-index (LI) of the left ventricular wall increases with the pressure registered (r = 0.95). At the same time the values for the right ventricular wall and the left atrium showed an inverse tendency corresponding to the fact that all indices decrease during normal growth. The relation of the indices is two to one for each atrium and its corresponding ventricle, as well as for the stressed left ventricular wall to the right one. The 3 H marked cells are found in groups with constant distances (75-85 microns). High LI are the consequences of the enlargement of these groups. There is no detectable relation to an anatomic structure. Some rare mitoses could be seen, especially in the left ventricular wall. Signs of a high biochemical activity are accumulations of mitochondria, high number of polysomes and large Golgi areas as well as laminas of ergastoplasm. The nuclei are extremely invaginated.

Morphometric, histochemical and autoradiographic studies on myocardial cells in experimental cardiac hypertrophy and ischemia

Experimental studies were conducted into 170 adult male Wistar rats for the purpose of analysis of cellular adaptation processes of the myocardium to acute ischemia. One group of the animals were exposed to physical endurance training, i.e. 180 h of swimming exercises, up to 3 h daily. Positive verification of cardiac hypertrophy was considered a measure of accomplished cellular adaptation. Training-induced increase of relative and absolute heart weight was 25 and 30%, respectively. Acute myocardial ischemia had been produced by ligature of the left coronary artery. There were no significant differences between trained and untrained animals for incidence and size of infarction and postoperative lethality, while cardiac decompensation was less often recorded from trained animals. To study cellular adaptation as well as differences between trained and untrained animals, tissue samples were taken from the non-ischemic part of the left ventricle and checked by means of histology, electron microscopy, morphometry, quantitative histochemistry, and histo-autoradiography 1, 2, 4, 7, and 14 days after occlusion of the coronary artery. The studies have shown endurance training to result in unambiguous modification of structural as well as functional response of the nonischemic heart. Included in such structural modification at cellular level are significant changes in mitochondrial membranes, sarcoplasmic reticulum, and T-system. Structural modification was reflected in changes to the oxidative enzymes and DNA metabolism. Different patterns of cellular reaction could be positively verified up to 14 days after myocardial infarction.

Papillary muscle structure-function relations in the aging spontaneously hypertensive rat

Isolated left ventricle papillary muscle mechanics and structure were studied in male spontaneously hypertensive (SHR) rats and two control groups of animals, the normotensive Wistar (NR) and the Wistar-Kyoto rat (WKY). Active tension and its first derivative (dT/dtmax) normalized for muscle cross-sectional area were increased in preparations from the SHR at all ages studied relative to control groups (P less than 0.01). However, when these parameters were normalized for myofibrillar cross-sectional area determined from electronmicroscopic point counting data, differences between groups were no longer significant. Force-velocity relations provided no evidence for a depression of shortening velocity at any load in the SHR at any age relative to the two control groups. The duration of mechanical activity, as determined by time-to-peak isometric tension and analysis of muscle force-velocity-time relations, was prolonged only in the 18 month old SHR (P less than 0.01). Thus, while changes in isolated muscle performance occur at a time when hemodynamic impairment is reported in the intact animal (male 18 month SHR), no evidence for depression of isolated muscle function is seen in the SHR at 6, 12 or 18 months of age.

Synergistic effects of diabetes mellitus and renovascular hypertension on the rat heart--stereological investigations on papillary muscles

The effects of combined renovascular hypertension and diabetes mellitus on the rat heart were investigated in order to detect possible synergistic effects of the two conditions. Hypertensive diabetic and hypertensive nondiabetic young male Wistar rats were compared with diabetic and non-diabetic controls. Since the normal body weight increase of the diabetic animals was markedly suppressed a weight-matched nondiabetic control group was introduced in addition. Hypertension was established for eight weeks by a surgical stenosis of the left renal artery, diabetes mellitus was maintained for four weeks after a single intraperitoneal injection of 75 mg/kg streptozotocin. Light and electron microscopic stereological parameters were obtained for the left ventricular papillary muscles. The whole hearts were also investigated histologically. Qualitative morphology failed to substantiate synergistic effects in the hypertensive diabetic rats. Vascular abnormalities were not observed. The stereological parameters, however, revealed microstructural reactions which were observed exclusively in the hypertensive diabetic group: the volume ratio of mitochondria-to-myofibrils was decreased, the surface-to-volume ratio of mitochondria was increased (reduction of mitochondrial size) and the mean cross sectional area of capillaries was decreased. Similar quantitative mitochondrial changes have been frequently described in long-standing hypertension, but in the present investigation, they were not found in the nondiabetic hypertensive group. It is therefore concluded that diabetes mellitus potentiates the effects of chronic pressure overload on myocardial cells. However, the myocardial fibrosis which has been found by other groups at later stages of hypertension and/or diabetes mellitus was not detected in the present study. The reduced mean cross sectional area of capillaries in hypertensive-diabetic rats may be correlated with early molecular changes of the myocardial interstitium or with early abnormalities of small arteries. Thus our stereological results support the hypothesis that a non-coronary hypertensive diabetic cardiomyopathy occurs in mammalian hearts.

Morphological reaction patterns in experimental cardiac hypertrophy--a quantitative stereological study

Four experimental models of myocardial hypertrophy were investigated in rats: 1. Mild hypertrophy induced by physical exercise, 2. mild hypertrophy induced by chronic pressure overload (24 weeks), 3. moderate hypertrophy induced by chronic pressure overload (8 weeks), 4. moderate hypertrophy in diabetes induced by chronic pressure overload (8 weeks). Stereological investigations on left ventricular papillary muscles disclosed different morphological reaction patterns: 1. The capillary bed of the myocardium responded differently in mild hypertrophy:physical training, but not mild chronic pressure overload, evoked neoformation of capillaries. 2. Mild hypertrophy and moderate hypertrophy induced by chronic pressure overload were not associated with quantitative structural reactions of myofibrils and mitochondria. Those alterations appeared, however, in hypertensive-diabetic rats with moderate hypertrophy. Our data provide further experimental evidence for the existence of a hypertensive-diabetic cardiomyopathy.

Ultrastructural morphometric analysis of myocardium from dogs, rats, hamsters, mice, and from human hearts

Volume densities of mitochondria, myofibrils, and unspecified cytoplasm were measured by ultrastructural morphometry in myocardium from dogs, rats, hamsters, mice, and in biopsied tissue from human hearts. Human myocardium was composed of 23% mitochondria, 59% myofibrils, and 18% cytoplasm. Volume densities for mitochondria were 22% for dogs, 28% for rats and hamsters, and 32% for mice. Myofibrillar volume densities were highest in dogs with 63%, 57% for rats and hamsters, and 49% for mice. Differences were significant between all except man and dog, and rat and hamster. In an extensive analysis of canine myocardium, it could be shown that the quantitative composition of tissue from the left ventricular free wall (anterior, lateral, posterior) and the papillary muscles was identical. There were also no differences between subepi- and subendocardium as well as the midmyocardium. Volume densities from longitudinal sections were identical to those from transversal sections. Fixation with glutaraldehyde by perfusion or immersion provided identical results. There were no differences between volume densities in samples from the left ventricular free wall (anterior, lateral, and posterior) in rats, hamsters, and mice. It is concluded that each mammalian species is characterized by a very typical quantitative composition of the myocardium. The increase in mitochondrial volume correlated well with the increase in heart rate and oxygen consumption in smaller animals. These quantitative data are regarded as the morphological correlate of the differing functional capacity of hearts from different species.

Age-dependent structural changes in the myocardium of rats. A quantitative light- and electron-microscopic study on the right and left chamber wall

Myocardial fine structure of 6-week-old and 2-year-old female Wistar rats was examined after fixation by perfusion. Qualitatively, lipid droplets, lipofuscin granules and myelin figures were found more often in the older animals. Quantitatively, the volume density of the interstitium of the right ventricular myocardium had significantly increased (52%) in the 2-year-old rats. In these animals a reduction (9%) in the volume fraction of mitochondria in the left ventricular myocytes was seen, while the volume fraction of myofibrils had increased by 10%. The numerical density of mitochondria had significantly increased in the left ventricular myocardium of the older rats by 42%. A decrease in the average size of a mitochondrion by 36% could be shown in the left and by 11% in the right ventricular myocytes of the 2-year-old rats. In these animals the myofibrillar transverse diameter diminished by 15% in the left and by 6% in the right ventricular wall, while the number of myofibrils had increased by 36% and 12%, respectively; these findings signify a close relationship in the number of mitochondria and myofibrils in myocytes. Quantitative alterations in the myocytes of aged rats are more obvious in the left than in the right chamber wall. A reduced mitochondria/myofibril ratio may contribute to the diminished functional adaptability of the aging heart.

Cardiac hypertrophy in rats after supravalvular aortic constriction. II. Inhibition of cellular autophagy in hypertrophying cardiomyocytes

Adult male Sprague-Dawley rats were killed by retrograde perfusion fixation 3, 7, 14, 21 and 35 days after supravalvular aortic constriction (n = 33) or sham-operation (n = 25). Subepicardial specimens of the left ventricular myocardium were evaluated by conventional electron microscopic morphometry, and in addition were examined for the occurrence of autophagic vacuoles (AVs) using large test areas (3.9 X 10(4) micron 2 per animal). The quotient of mitochondrial to myofibrillar volume fraction was largely unchanged during hypertrophy but was reduced by 25% compared with controls after termination of growth at 35 days. During the process of hypertrophy which eventually led to an increase in average single cell volume of the cardiomyocytes by 78%, the volume fraction and the numerical density of AVs was significantly lower than in sham-operated rats. The most striking difference was observed 7 days after the operations, the stage at which the growth rate of the cardiomyocytes relative to controls was at its maximum of 4.5% per day. At this point the volume fraction as well as the numerical density of AVs were reduced by about 50% compared with controls. At 14 and 21 days after operation, when the relative growth rate of the hypertrophying cardiomyocytes was still 2% and 1% per day, the AV volume fraction was reduced to a lesser extent (by 47% and 28%, respectively). After termination of adaptive growth at 35 days significant differences in fractional volume and numerical density of AVs were no longer detectable. These results suggest that degradation of cytoplasmic components is inhibited in cardiomyocytes undergoing hypertrophy. Such an anticatabolic reaction seems to play an important role in establishing the positive balance of cellular metabolism generally required for growth processes.

Carbon monoxide inhalation: effect on heart cytochrome c in the neonatal and adult rat

Male rats, 5 and 90 d of age, continuously inhaled 500 ppm CO [40% carboxyhemoglobin (COHb)] for 5.5-8.0 wk. Cardiomegaly and polycythemia developed as previously reported. Heart weight gain in young and old rats treated with CO was accompanied by increased cytochrome c content (nmol) in both left ventricle (LV) and right ventricle (RV) relative to controls. Cytochrome c concentration (nmol/g wet weight), however, was significantly depressed in LV and RV of young CO-exposed rats relative to controls, while there was no change in LV and RV of the old CO-exposed group. LV cytochrome c concentration was significantly higher than that of RV in both young and old, CO-exposed and control rats. On the other hand, cytochrome c concentration in young and old control LVs was similar, as was cytochrome c concentration in RVs of young and old control rats. Three additional experiments were carried out with 5-d-old rats inhaling 500 ppm CO, for 47 and 25 d. These also showed the increase in myocardial cytochrome c content and compromise of cytochrome c concentration, and both changes were greater with longer exposure.

Selective effects of alpha-methyldopa on myocardial cell components independent of cell size in normotensive and genetically hypertensive rats

Alpha methyldopa has been shown to modify left ventricular mass and normalize mitochondria/myofibrils volume ratio in spontaneously hypertensive rats (SHR) when administered during the stage of developing cardiac hypertrophy (Tomanek et al., Cardiovas Res 23: 173, 1979). To evaluate the long-term effects of this antihypertensive agent, the drug was administered to SHR and normotensive (WKY) rats between the ages of 1 and 12 months. In another group of SHR and WKY, treatment was delayed until the age of 12 months and the animals were then treated for 3 months. Treatment with alpha-methyldopa had similar effects on systolic blood pressures in both SHR groups; group means (+/- SEM) were 151 +/- 1 in the long-term treatment group and 157 +/- 5 in the delayed treatment group compared to 178 +/- 4 and 176 +/- 3 for their respective controls. While left ventricular weight and cell size were significantly lower after early long-term treatment (compared to nontreated SHR), delayed treatment had no significant effect on these indices of left ventricular mass. Despite the effectiveness of early long-term treatment in modifying left ventricular mass, the relative volumes of mitochondria and myofibrils, as well as other cellular components (sarcoplasm), were not altered. In contrast, delayed treatment caused a significant increase (approximately twofold) in relative sarcoplasmic volume and a decrease in relative myofibrillar volume in both SHR and WKY. These findings indicate that shifts in the relative volumes of intracellular components after alpha-methyldopa are independent of cell size and blood pressure. Furthermore, the data suggest that the effects of alpha-methyldopa on the myocardial cell are dependent on or influenced by factors associated with the development or stabilization of hypertrophy and/or age.

Giant mitochondria in the human myocardium--morphogenesis and fate

Electron-microscopical examination of myocardial biopsy material obtained from a 58-year-old man revealed giant mitochondria having a length of 30 micron. Such giant mitochondria (also called megamitochondria) evolve by fusion of the membranes of numerous large individual organelles. Initially they are polymorphous and of diverse shapes, but later they are seen to be arranged among and parallel with the filaments of the myocardial fibres, where they present a smooth, cigar-like appearance. Deposits of glycogen in the giant mitochondria result from the accidental inclusion of glycogen granules during fusion. The abundance of cristae, which often form dense stacks in the megamitochondria, is evidence for the genuine synthesis of new cristal material. The aetiological and exact pathogenetic mechanisms of the evolution of giant mitochondria in the myocardium, as also their function, remain unclear. Particularly large specimens are obviously inefficient and disturbing to the cell. They are degraded by autophagy.

Ultrastructural and morphometric study of the human heart muscle cell in acute coronary insufficiency

In 13 patients with acute coronary insufficiency (intermediate syndrome, postinfarction angina, and progressive angina), samples of the ischemic area of the myocardium were studied with the electron microscope and by morphometric methods in order to describe quantitatively the mitochondrial population. Three indices were measured: the fractional volume of the mitochondrial compartment of the cytoplasm, the number of mitochondria per unit volume of heart tissue, and the average individual mitochondrial volume. As a control, the same study was performed on samples obtained from patients with chronic coronary insufficiency and mitral stenosis. In all the ischemic hearts the most conspicuous ultrastructural modification of the muscle cells consisted in an irregular distribution of the mitochondriranules. Generally, odd shaped mitochondria were found. The modifications were not diffuse, and almost normal heart muscle cells were seen alongside deeply altered ones. In addition a definite decrease in the fractional volume of the mitochondrial compartment was found, which was apparently due to a decrease in the number of mitochondria per unit volume of cytoplasm. The average individual mitochondrial volume was similar in acute coronary insufficiency and in the control cases. On the basis of this evidence it is postulated that in sublethal ischemia definite ultrastructural modifications of the heart muscle cells are associated with a decrease in the number of mitochondria per unit volume of cytoplasm.

Cellular mechanisms of normal growth in the mammalian heart. II. A quantitative and qualitative comparison between the right and left ventricular myocytes in the dog from birth to five months of age

This paper describes and contrasts the changes in myocytes taken from the right and left ventricules of dog heart over the first 5 months of life. The development of the two populations of cells differs in important respects: sarcomeric volume, the proportion of the myocyte occupied by the contractile apparatus, and the volume and surface area of the transverse tubular system all were greater on the average in the left than in the right ventricle (P less than 0.001). Other intracellular structures also changed significantly as development progressed, but did so in both chambers; the surface area and surface-to-volume (s/v) ratio of both right and left ventricular myocytes increased with age (P less than 0.001) as did mitochondrial and mitochondrial-myocyte volume (P less than 0.001). The surface area (P less than 0.01) and the s/v ratio of the mitochondria (P less than 0.001) also increased with development. Nuclear and nuclear myocyte volume grew smaller with age in both chambers (P less than 0.002), as did the surface area (P less than 0.001) and the s/v ratio of the nucleus (P less than 0.01). Not only does myocyte composition change quantitatively, striking changes in intracellular architecture and the appearance and arrangement of intracellular organelles occur during postnatal life.

[Ultrastructural morphometric analysis of hypertrophied human myocardial left ventricles (author's transl)]

Biopsies of hypertrophied human myocardial left ventricles were investigated morphometrically. The diagnoses of the patients were stenosis of the aortic valve, aortic insufficiency or a combination of both lesions. The results were compared with those from normally loaded human left ventricles. There are no differences on light microscopical level between the volume densities of interstitial tissue and of heart muscle cells in the three groups of patients. A significant diminution of the volume density of the nuclei (P less than 0.001) and the number of nuclei per test area (P less than 0.001) when compared with normal groups suggests an increase in volume of the single heart muscle cell. The ultrastructural study shows marked increase in volume density of myofibrils (P less than 0.0001), with accompanying decrease in the volume densities of mitochondria (P less than 0.0001) and the remaining cytoplasm (P less than 0.001). A gross decrease in the surface area of mitochondria (P less than 0.001) and of cristae mitochondriales (P less than 0.0001) is found. The morphological equivalents of this result are numerous stages of mithochondrial destruction including cristolysis. All myocardial weights were beyond the "critical heart weight".

[Ultrastructural morphometric analysis of normally loaded human myocardial left ventricles from young and old patients (author's transl)]

An ultrastructural and morphometric analysis was performed on human myocardial left ventricle, obtained during surgical heart operations on normally loaded ventricles. The diagnoses of the patients were a) Persistant foramen ovale b) Atrial septal defect stage (I.-II) c) Mitral stenosis (stage III.-IV.). The median values of left ventricular pressure were not pathologically elevated. The patients were divided in 2 groups, the younger one ranging from 5-15 years, the older from 42-78 years. It was shown that the volume density of the interstitial tissue does not differ with the aging process. The number of the nuclei per test area of the heart muscle cells decreased within age (P less than 0.001). This finding suggests a decreasing process in the number of the heart muscle cells and an increase in size of the individual myocardial cell. Increase in the volume density of myofibrils was demonstrated at electron microscopical level with aging (P less than 0.02). The volume density of mitochondria is the same in both groups, whereas the volume density of the remaining cytoplasm (without myofibrils and mitochondria) decreases (P less than 0.05). The numberical density of the mitochondria increased in the older patient group (P less than 0.001).

Nuclear DNA of myocardial cells in the periphery of infarctions and scars

In 20 hearts the enlargement of muscle fibers and the increase in nuclear DNA is studied in the periphery of fresh and healed infarctions. The data of attack is verified by ECG records in most cases, five had passed undiagnosed. Selective cytophotometry is performed by measuring the largest nucleus in each of 50 fields of comparable density. Since significant differences in polyploidization exist between the control regions of hearts of similar weight primarily regions of the same heart are compared. No differences are observed in five hearts with infarctions about one week old. After five to six months the enlargement of the fibers is significaant (P less than 0.0005) while the increase in polyploidy is still slight (P less than 0.15). In all cases with scars one to nine years old the enlargement of fibers is significant (P less than 0.0005) while the increase in DNA is significant in most of them (5 X P less than 0.0005, 3 X P less than 0.005, 2 X P less than 0.01). In a case with two lesions, one posterior five (P less than 0.0005) and one anterior seven years old (P less than 0.0005), there is still slight increase in polyploidy with age (P less than 0.1). In the five undiagnosed cases only one has no significant increase in DNA. There is no correlation found between the enlargement of fibers and the increase in polyploidy in this limited number of cases.

Different fractions in the normal and hypertrophied rat ventricular myocardium: an analysis of two models of hypertrophy

Long-term hemodynamic overload of the heart leads to an increase in myocardial mass. In most cases it is not known to what degree the single components in the myocardium (water, protein, nonprotein substance) increase. As an answer to the overloading of the myocardium, many authors have established an intensification in the synthesis of myocardial proteins. It is, however, little known which proteins are then more intensively created and accumulated. This study examines the dynamics of the protein and nonprotein content as well as of single protein fractions (sarcoplasmic, myofibrillar, and stromal) in both hypertrophied and normal tissue from rat myocardia. The results revealed that in Goldblatt rats, 4-24 weeks after stenosis of one renal artery, no noteworthy differences in the relationships of protein and nonprotein content were caused by hypertrophy (34-54%) due to left ventricular pressure overload. The same is true of the tissue from moderately hypertrophied myocardia (12-17%) of rats exercised for several weeks by swimming training. Determination of hydroxyproline concentration showed that significant differences in the content of the collagen tissue in relation to control animals of the same age occurred only in Goldblatt rats 24 weels after operation. However, greater alterations in the concentrations of various protein fractions could be registered. The increase in the concentration of myofibrillar proteins in hypertrophied myocardial tissue is of particular significance and is to be considered as an adaption of the muscle to the increased mechanical demands. Certain changes regarding the relation of the single components within the myofibrillar fraction (relation of actomyosin concentration to T-fraction; relation of both components to total fraction), whose cause and significance is as yet unclear, could be observed.

Quantitative changes of canine diaphragm muscle cells following electrostimulation

1. In 12 dogs the right part of the diaphragm was stimulated 4, 5, 8, 11, and 14 weeks by means of a pacemaker. 2. Essential findings have been the increase of the amount of glycogen after 5 weeks, the increase of myofilaments per myofibril after 8 weeks, and the increase in the share of mitochondria in the 11th week. After 14 weeks all values have reached again their initial level as the result of an adaptation. 3. From the quantitative structural findings it can be taken that the diaphragm musculature is not changed by the electrostimulation in such a way that the functional preconditions for covering heart muscle deficiencies by diaphragm flaps are given.

Myofibrillar mass in rat and rabbit heart muscle. Correlation of microchemical and stereological measurements in normal and hypertrophic hearts

A sequestered fraction of myofibrillar magnesium presumably bound to thin filaments during polymerization of actin was used to determine myofibrillar mass in rat left ventricles and rabbit hearts. Myofibrillar volume was also determined by stereological measurements on electron micrographs of rat ventricles. Myofibrillar Mg (1.11 mmoles/kg dry ventricle) can be determined in glycerinated ventricle either by measuring 28 Mg-inexchangeable Mg or Mg remaining after extraction with EDTA, KCl, and a nonionic detergent. These measurements, combined with the Mg content of myofibrillar suspensions similarly extracted (3.2 mmoles/kg protein), indicated that myofibrillar mass was 347 g myofibrillar protein/kg dry ventricle. In rabbit hearts, increases in myofibrillar Mg per unit dry weight were as follows: auricular appendage < right ventricle < left ventricle ⋍ interventricular septum. After production of left ventricular hypertrophy in rats by constriction of the ascending aorta, both myofibrillar Mg and volume increased within 24 hours. After 10 or more days, myofibrillar Mg and myofibrillar volume increased proportionately more than tissue dry mass and cell volume, and the ratio of mitochondrial volume to cell volume decreased.

Disorder in excitation-contraction coupling of cardiac muscle from cats with experimentally produced right ventricular hypertrophy

The contractile and electrical activity of papillary muscles from hypertrophied right ventricles of cats with artificial stenosis of the pulmonary artery was investigated. Contractility was considerably decreased along the entire force-velocity relationship, whereas no measurable alterations could be detected in the electrical activities as recorded by intracellular microelectrodes. By supramaximal Ca 2+ activation, the contractility of both the hypertrophied and the normal control preparations was increased to about the same final value. These findings are consistent with the concept that a disorder in the mechanism of excitation-contraction coupling underlies the depressed contractile state of hypertrophied cardiac muscle. In addition, it could be shown that the increase in volume of each cellular unit is clearly related to the decrease in contractility. This can tentatively be explained by the following assumptions. If the amount of Ca 2+ entering the cell per unit area is not changed in hypertrophy, then in a cell of increased diameter, the amount of Ca 2+ distributed per unit cell volume will be diminished. Since the excitation-contraction coupling of the heart is very sensitive to Ca 2+ , this Ca 2+ deficit should be reflected in a depression of contractility.