Differences in myocyte subpopulations from segments of the thoracic aorta and their modifications with age and hypertension in the rat.

Smooth muscle cells obtained from three distinct segments of the thoracic aorta of both Wistar Kyoto (WKY) and Spontaneously Hypertensive Rats (SHR) taken at different stages of development were studied in terms of their volume, DNA content in single cell suspensions, and doubling time in primary cultures. The proliferative activity and mean cell volume of myocytes from WKY rats increase along the thoracic aorta in a gradient from the aortic arch to the diaphragm. The slope of this gradient is increased in SHR because of an extension of the area that contains myocytes with low proliferative activity in primary cell culture and large cell volumes in suspension. Tetraploid myocytes are found in both strains and their proportions are larger in SHR than in WKY, specifically after the onset of hypertension. However, they appear to be evenly distributed along the thoracic aorta with a size distribution that is included in that of the diploid cells from the same area. It is suggested that changes in the structural properties of the aortic-cell compartment, associated with maturation and hypertension, reflect quantitative changes in the relative proportions of several myocyte subpopulations within the aorta of the rat.