Effects of endothelin-1 and vasopressin on resistance arteries of spontaneously hypertensive rats.

Previous studies have shown an impairment of responsiveness of resistance arteries to endothelin-1 in experimental hypertensive rats. This study was undertaken to demonstrate whether responses were also blunted in adult 20-week-old spontaneously hypertensive rats (SHR). Resistance arteries from the mesenteric vascular bed exhibited normal active tension responses to endothelin-1 and arginine vasopressin, and exaggerated responses to norepinephrine. Since the media was thicker in SHR, media stress responses to endothelin-1 and arginine vasopressin were significantly impaired, while norepinephrine media stress responses were similar in SHR and Wistar-Kyoto rats (WKY). Active pressure responses to endothelin-1, arginine vasopressin, and norepinephrine were significantly amplified by the narrowed lumen of blood vessels in SHR. Additionally, media cross-sectional area was similar in SHR and WKY, but was greater in SHR when normalized for the smaller body weight of the hypertensive rats. These results demonstrate the presence of remodeling in resistance arteries of 20-week-old SHR, and show that the altered morphology of these blood vessels may significantly amplify impaired wall stress responses to endothelin-1 and arginine vasopressin, which may contribute to elevation of blood pressure.