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I Medugorac

Publications and source records attributed to I Medugorac.

26 records · Page 2Linked to original sources
PubMedDate not supplied

Mechanics of the isolated ventricular myocardium of rats conditioned by physical training.

Force-velocity relations from after-loaded contractions, from isometric and isotonic QR experiments, resting-tension curves and biochemical analyses were conducted on sixteen trabecular muscles (SH) from hearts of rats conditioned by eight weeks of swimming training (increase in heart weight 8%), and compared to a control (CH) of eighteen trabecular muscles. (SH) showed increased tension development (p less than 0.01), whereas the diastolic properties remained almost unchanged. Analysis of the amount of hydroxyproline did not prove any variation. Vmax of (SH) was only slightly increase when there was a singificnat rise in actomyosin and myosin ATPase activity, while PO of the force-velocity relations of (SH) on the x axis (tension) shifted clearly to the right (p less than 0.01). Consequently, the maximum instantaneous power of (SH), expressed by the maximum rectangular plane under the force-velocity curve, increased considerably (p less than 0.01) in comparison with (CH). The experiments show that haemodynamic load induced by training does not alter the passive properties of the myocardium, but does bring about an increase in the contractile capabiltiy.

Actomyosin↗
PubMedDate not supplied

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.

Animals↗
PubMedDate not supplied

Connective tissue content and myocardial stiffness in pressure overload hypertrophy. A combined study of morphologic, morphometric, biochemical, and mechanical parameters.

We investigated samples of left ventricular myocardium from Goldblatt II (4 and 8 weeks after operation) and spontaneously hypertensive rats (SHR; 40 and 80 weeks old) by histological and morphometric methods. From the same hearts, the distensibility of the left ventricular papillary muscle was analyzed by means of resting tension curves, and the collagen content of the whole left ventricular wall was determined by means of hydroxyproline concentration. In all groups, myocardial fibrosis was observed to accompany myocardial hypertrophy. The severity of fibrotic lesions increased with the duration of hypertension, and, in late stages, degenerative changes of cardiac myocytes were found. Morphometric determinations and chemical analysis of the hydroxyproline concentration revealed a decrease in myocardial muscle content, which was paralleled by an increase in collagen content when compared to the respective controls. In general, morphometric and chemical findings correlate with increased myocardial stiffness observed during mechanical measurements in isolated papillary muscle preparations from the same hearts. Differences were found, however, between chemical analysis and mechanical measurements in the 40-week-old SHR group, which may result from different patterns of collagen distribution between interstitium, perivascular spaces, and the walls of blood vessels. The comparison between histological, morphometric, chemical, and physiological data shows that (1) cardiac hypertrophy of Goldblatt and SH-rats is accompanied by myocardial fibrosis, and (2) changes in passive elastic properties of myocardium is better reflected in morphometric than in chemical analysis.

Animals↗
PubMedDate not supplied

Characterization of intramuscular collagen in mammalian left ventricle.

Left ventricular collagen of various mammals (cat, cow, dog, pig, and rat) was successively extracted with neutral salt, and dilute acid solutions, and limited pepsin digestion. The distribution of the various types of collagen molecules in pepsin-solubilized ventricular collagen was analyzed electrophoretically on SDS-polyacrylamide gels in the presence of 3.6 M urea. Yields of dilute-acid-soluble collagen were only 0.4 to 0.6% of the total ventricular collagen, and less than 0.1% with neutral salt solution. Approx. 55-90% of the total collagen was extracted by limited pepsin digestion. Disc patterns of pepsin-soluble collagen revealed the presence of dimeric and trimeric components, as well as higher-molecular-weight aggregates in all samples of nonreduced and reduced ventricular collagen. Taken together, these findings suggest the presence of an extensive interchain and intermolecular cross-linking network in left ventricular collagen. Comparison of electrophoretical disc gel patterns of reduced and nonreduced pepsin-solubilized collagen indicated that left ventricular collagen is heterogenous in nature, consisting of a mixture of type I and type III collagen. It was evident that primarily type I components occur in ventricular collagen. The components of type III collagen molecules occurred in all investigated left ventricles in varying and consistently appreciably lower amounts. The proportions of type III and type I collagen vary in left ventricular tissue of different species.

Animals↗
PubMedDate not supplied

Quantitative determination of cardiac myosin subunits stained with fast green in SDS-electrophoresis gels.

In the present study a procedure is described which permits simultaneous relative quantification of all myosin subunits in the same fast green stained electrophoresis gel. The relative protein quantification can be performed successively in the same gel using densitometry and the elution method, respectively. Thus, the results obtained with one method can be checked with the other. This procedure provided reliable estimates of the stoichiometry of cardiac myosin subunits within a range of about 20--110 micrograms of total myosin protein per elctrophoresis gel.

Actomyosin↗
PubMedDate not supplied

The behavior of some enzymes of the hypertrophied and postnatally developing myocardium of the rat.

The present study was undertaken in order to investigate the behavior of lactate dehydrogenase (LDH) and hexokinase (HK) in the mechanically overloaded and the postnatally developing left ventricle of the rat. In Goldblatt rats (GBR) 2 to 4 months after operation total LDH activity was decreased by 7%, accompanied by an isoenzyme shift towards a higher M proportion. Swimming rats (SR) showed an 11% increase in LDH activity. HK activity was increased by 14% in GBR and unaltered in SR. Histochemical investigations revealed no indication of heterogeneous alterations in various areas of the myocardium. During postnatal development, a gradual increase of activity and H subunit proportion of LDH were observed. HK activity was increased after one week, but underwent a slow decreased thereafter. These changes are interpreted as processes of adaptation to the conditions of extrauterine life.

Aging↗