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Abstract
This work was performed to study the possible histological changes that may occur in the cardiac muscles of male albino rats from birth till aging. For this purpose, forty healthy male albino rats were utilized. The animals were classified into four age groups (ten rats each); Group A: Neonatal animals (0-3 days old rats), Group B: Prepubertal animals (4-5 weeks old rats), Group C: Adult animals (4-6 months old rats), and Group D: Senile animals (12-18 months old rats).
The animals were anaesthetized, thoracotomy was performed, and the hearts were dissected out. Paraffin sections were prepared, stained with H & E stains as well as Masson’s trichrome stain, and examined by light microscope. Also, minute specimens were rapidly taken and processed to obtain semithin sections stained with toluidine blue to be examined by light microscope, and ultrathin sections stained with uranyl acetate, to be examined by TEM.
The results of light microscope examination of the cardiac muscles of all age groups of rats revealed cardiac muscle fibers in different directions lined by endocardium and covered by epicardium. The muscle fibers were branched and showed eosinophilic sarcoplasm and cross striations in the form of alternating dark and light bands. The nuclei were oval and central. The intercellular spaces showed blood capillaries, collagen fibers, and fibroblasts. Ultrastructurally, longitudinally-sectioned cardiac myocytes demonstrated long, parallel, and striated myofibrils. The myofibrils showed A, I, and H bands as well as Z and M lines.
Examination of the newborn rat ventricles showed the cardiac myocytes with large euchromatic nuclei. Some of them were binucleated. Numerous small mitochondria appeared as clusters in the perinuclear regions and between the myofibrils. Intercalated discs were represented by disc-like zones between adjacent myocytes. Few collagen fibers were seen in the intercellular spaces.
Examination of the prepubertal rat cardiac muscle showed that some cardiac myocytes had irregularly-outlined nuclei while others were binucleated. The sarcoplasm showed numerous mitochondria and glycogen granules. Well-developed intercalated discs were identified between adjacent myocytes. The transverse portion of the disc showed adherens junctions while the longitudinal portion displayed gap junctions. Collagen fibers were detected in the intercellular spaces and were more dense in the epicardium.
The cardiac myocytes of adult rats revealed elongated euchromatic nuclei. However, some myocytes displayed irregular nuclei. Numerous mitochondria appeared around the nucleus and as rows between the myofibrils. Some mitochondria were large and distorted. Glycogen granules as well as sarcoplasmic reticulum were seen in the sarcoplasm. T-tubules appeared at the level of Z-lines. Well-developed intercalated discs were identified between adjacent myocytes. Collagen fibers were observed in the intercellular spaces and around blood vessels.
Examination of senile rat ventricles revealed some myocytes with irregularly-outlined nuclei. Clear perinuclear regions were observed in some cells. Other cells showed myofibrils with areas of disorganized or lost microfilaments. Mitochondria appeared between the myofibrils. Some of them were large, deformed and displayed vacuoles of different electron densities. Also, the sarcoplasm showed some vacuoles surrounded by membrane whorls. Besides, some electron dense bodies variable in size and shape were seen in the sarcoplasm. Well-developed intercalated discs with their transverse and longitudinal portions appeared between myocytes. There was a marked increase in collagen fibers in the intercellular spaces and around blood vessels which had thickened wall. Fibroblasts were also observed in the intercellular spaces.
It is concluded that several age-related changes occur in the cardiac muscle that may lead to development of cardiac incompetence following loading in old age.