DYNAMICS OF ENDOTHELIUM-MUSCLE CELL CONTACTS IN THE CORONARY-ARTERY OF THE DOG IN ONTOGENY

The myo-endothelial area in the coronary artery conduit was described in 3 developmental stages: in fetuses, newborns, and adult dogs. Trans mission and scanning electron microscopy were used for the study, and morphometry was used for quantitative evaluation. In all three stages, the internal elastic lamina was found to be fenestrated. Endothelial cells and smooth muscle cells (SMC) approached the fenestrae, and prot rusions of one or both cells entered into the fenestrae. In some place s contacts between endothelial and SMC were found. The patterns of mut ual approaches of smooth muscle and endothelial cells, as well as the entering into the fenestrae were similar in all three stages. The myoe ndothelial contacts were counted per 100 mu m inner circumference of t he coronary artery and the numbers observed, i.e. 5.17 +/- 0.50 in fet uses, 1.94 +/- 0.17 in newborns and 0.33 +/- 0.09 in adult animals, pr oved clearly that the frequency of myo-endothelial contacts, highest i n fetuses, decreases with age. With regard to the dual control of the coronary smooth muscle and/or diameter, it is noteworthy that an oppos ite trend can be observed in the development of innervation of the cor onary artery: the autonomic nerve fibres with varicosities are missing in the coronary wall 1 week before birth, while after birth their num ber keeps increasing. Remarkable enough is also the difference in dist ances between the endothelium and SMC on the one hand and nerve varico sities and SMC on the other. The above facts indicate a prevalence of endothelial control of coronary diameter.