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stances directly influence cardiac metabolism, growth, contractile performance, and

rhythmicity of the adult heart.

In recent years, endothelial progenitor cells that contribute to angiogenesis have

been identified as a circulating cell population in the peripheral blood. They are

derived from the bone marrow [ 106 ]. Endothelial progenitor cells are rare in the

circulation, but they can be mobilized into the circulation from the bone marrow by

vascular trauma or some types of cytokines. They may be associated with some

degenerative diseases, such as progressive progenitor cell deficits that may contrib-

ute to the development of atherosclerosis [ 107 ]. The study of Rehman et al. [ 108 ]

demonstrated that exercise can acutely increase two distinct cell populations that are

known to be involved in angiogenesis and endothelial repair. These include circulat-

ing endothelial progenitor cells, which may supply new endothelial cells to the vas-

culature, and circulating angiogenic cells, which secrete growth factors that promote

endothelial growth and angiogenesis. Furthermore, Adams et  al. [ 109 ] confirmed

that there is an increase in the number of circulating endothelial progenitor cells in

patients who undergo exercise-induced myocardial ischemia after exercising on an

electronically braked bicycle. It seems that an ischemic stimulus may trigger the

release of endothelial progenitor cells from the bone marrow in the peripheral blood.

These results are in accordance with a recently published meta-analysis of 16 differ-

ent studies [ 110 ]. This meta-analysis found that exercise training improved endo-

thelial function in patients suffering from heart failure. It is likely that bot, acute and

chronic exercise have the potential to mobilize endothelial progenitor cells, which

are important players in endothelial repair.

Pericytes (Rouget cells) are cells closely encircling endothelial cells in capillar-

ies and microvessels. They have a branched, flattened cytoplasm and oval nuclei.

The antigenic profile is important for immunohistochemical identification, and it

includes the expression of CD146, PDGFR-beta, and alkaline phosphatase [ 111 ]. In

general, pericytes are involved in the preservation of vascular homeostasis, includ-

ing the regulation of blood flow, angiogenesis, structural stabilization of the vascu-

lature, and vascular permeability [ 112 ]. However, the functions of pericytes are

varied. The initial hypothesis that pericytes are only supportive perivascular cells

can now be considered obsolete. These cells should be considered to be

heterogeneous, tissue-specific, and multipotent populations with myogenic, osteo-

genic, chondrogenic, and adipogenic potentials. In myocardial ischemia, pericytes

have been shown to be involved in fibrosis and scar formation [ 112 ]. In skeletal

muscle, pericytes accumulate in muscle as a type of mesenchymal stem cells and

they contribute to the formation of new muscle fibers and vessel remodeling follow-

ing exercise (which increases the diameter of vessels and arteriolar density) [ 113 ].

Acknowledgments This study was supported by a grant from the Slovak Research and
Development Agency No. APVV-0434-12 for “Morphological characterization of reparative and
regenerative mechanisms in myocardium during chronic diseases.”

8 The Non-cardiomyocyte Cells of the Heart. Their Possible Roles...