Orientation of arterial smooth muscle and strength of contraction of aortic strips from DOCA-hypertensive rats.

The functional orientation of vascular smooth muscle in the walls of aortae of DOCA-hypertensive and normotensive rats was determined by measuring the maximum force-generating capacity of strips cut at various angles from their aortae. The greatest tension produced by strips of aortae of either group was generated by strips cut perpendicular to the long axis of the artery. Strips of aortae from either group produced less tension if cut at different angles with respect to the circumferential axis. Cut at any angle, the strips of aorta from DOCA-hypertensive rats produced less tension than those from control rats at the same preload. In length-active stress studies, stress developed by strips cut from DOCA-hypertensive rats was less than that of control rats throughout the entire range of resting lengths. Stereologic analysis of histologic sections of aortae demonstrated a decrease in the volume fraction of smooth muscle in the media of aortic wall. No differences between the carotid arteries of the same DOCA-hypertensive and normotensive rats were found in the proportion of water (by weight) in their walls.