Vascular structure and smooth muscle contractility in experimental hypertension.

The possible role of vascular structure as a pathogenetic factor in hypertension has been investigated by determining the media dimensions in resistance (mesenteric, renal, cerebral, and femoral) vessels taken from a variety of hypertensive rat models [spontaneously hypertensive (SHR), stroke-prone SHR (SHRSP), and one-kidney, one-clip renal hypertensive rats]. Resistance vessels from hybrid SHR/Wistar-Kyoto rats (WKYs) and from hybrid SHRSP/WKYs were also examined. In all cases, there was a correlation between media dimensions (media cross-sectional area or media/lumen ratio) of the resistance vessels (internal diameter of 100-300 microns) and the blood pressure of the rats concerned. Furthermore, the media of the SHR mesenteric resistance vessels were only increased in vessels larger than about 100 microns, indicating that structural changes were not to be expected in the microvasculature. These results suggest a causal relationship between blood pressure and the structure of the proximal resistance vasculature. Evidence that the increased structure is not solely a consequence of the increased pressure has been obtained from antihypertensive therapy experiments in which SHRs treated with hydralazine had resistance vessels with increased media/lumen ratios even though the animals had never become substantially hypertensive. The results point to a possible role for vascular structure in the development of hypertension.