The study of isolated preparations of experimental white rats of 14 months and older reveals that the longitudinal orientation of cardiomyocytes is replaced by an angular orientation in older mice. The number and structural integrity of myofibrils occupy one of the leading places in the regulation of the contraction-relaxation cycle and the implementation of the adaptive capabilities of the myocardium in the normal functioning of cardiomyocytes. Our experimental studies aim at describing the quantitative a n d m o r p h o l o g i c a l c h a r a c t e r i s t i c s o f m y o f i b r i l s i n r a t s o f t w o a g e g r o u p s a n d a n a l y z i n g t h e morphological and functional results. Isolated heart preparations were examined in two age groups of white rats (middle -8-14 years; elderly -14 months and more. The number of rats in each group amounted to six) using different histological staining methods. The results obtained show that, compared with middle-aged rats, the development of degenerative changes in myofibrils is observed in old rats, which is manifested in structural inferiority and quantitative reduction. Degenerative changes revealed with age at the intracellular level can be considered an important morphological basis for the formation of functional heart failure and the depletion of adaptive capabilities.

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BACKGROUNDDespite recent achievements regarding the pathogenesis of leiomyoma, the exact mechanisms and role of angiogenesis are not well understood. According to the existing evidence, the excess of steroids, their influence on the apoptosis mechanisms, and the expression of local growth factors may stimulate the formation of leiomyomas in women of reproductive age. OBJECTIVES The present study aimed to ascertain the pathophysiological mechanisms underlying angiogenesis disorders and shed light on the function of steroids in this process. METHODS The central and peripheral parts of the 42 postsurgical uterine leiomyoma nodes were examined with the aim of assessment of angiogenetic changes in the proliferating, recurrent, and latent leiomyomas, using (i) hematoxylin and eosin (H and E), and Masson's trichrome stain of formalin-fixed paraffin-embedded sections, and (ii) immunohistochemistry evaluation of estrogen receptor (ER), progesterone receptor (PR), and CD34 (transmembrane phosphoglycoprotein protein encoded by the CD34) markers. RESULTSThe small proliferative leiomyomas (1-2 cm) are characterized by prominent angiogenesis with a dominance of small and medium-caliber aberrant vessels. The tendency to decrease intranodal blood vessels with the growth of tumor nodes (3-4 cm in size) indicates to depletion of resources of the autonomous vascular collector (tumor bed), after which the leiomyomata may enter the recurrence phase with the formation of a new locus of angiogenesis. The uniform distribution of the blood vessels throughout the proliferative leiomyoma node indicates that tumor growth occurs throughout the whole vascular collector. The depletion of the capacity of angiogenesis has an inhibitory effect on the growth of latent nodes and increases the risk of the secondary lesion because of blood supply alterations. CONCLUSIONS Angiogenesis plays an important role in the progression of leiomyoma. The tumor growth occurs throughout the whole vascular bed (in the central and peripheral parts of the leiomyomata) and not from a single smooth muscle cell. KEYWORDS CD34 marker; estrogen receptor (ER); latent leiomyoma; progesterone receptor (PR); proliferating leiomyoma; recurrent leiomyoma; uterine body leiomyoma.