Endogenous angiotensin II enhances phenylephrine-induced tone in hypertensive rats.

Subthreshold concentrations of angiotensin II (Ang II) potentiate agonist-induced tone in a variety of blood vessels. We measured in vivo the mesenteric artery diameter and blood flow in 12-week-old normotensive Wistar-Kyoto (WKY) rats (n = 20) and spontaneously hypertensive rats (SHR, n = 20); systemic blood pressure was monitored continuously. Phenylephrine (10 mumol/L) superfused on the exteriorized mesentery reduced arterial diameter from 480 +/- 40 to 256 +/- 18 microns (P