Resistance vessel abnormalities in spontaneously hypertensive rats.

This paper summarizes and discusses investigations in the author's laboratory designed to determine whether certain cardiovascular parameters which differ in 12- to 14-week-old spontaneously hypertensive rats (SHR) and age-matched Wistar-Kyoto rats (WKY) are associated with the cause of the difference in the blood pressures of these animals. The investigations include age studies, antihypertensive-treatment studies, studies of hybrid SHR/WKY, as well as studies of renal hypertensive and of normotensive Wistar rats. The parameters studied include heart/body-weight ratio and the media/lumen ratio and calcium sensitivity of the norepinephrine response of mesenteric resistance vessels (internal diameter 150-200 micron). The results indicate that heart/body-weight ratio and media/lumen ratio of resistance vessels are increased in 12- to 14-week-old SHR and suggest that this is due primarily to genetic factors rather than to the increased blood pressure. Furthermore, these structural abnormalities do not appear to be a sufficient cause of the increased blood pressure. On the other hand, the calcium sensitivity of the resistance vessels, which is also increased in SHR, may be associated with the genetic factors responsible for the increased blood pressure.