Fig. 1.

Phenylephrine-induced changes in cardiovascular parameters. Time course of changes in the MAP (top) and the baroreflex index (Δ heart rate/Δ MAP) (bottom) induced by sustained intravenous infusion of PE. Data are presented as mean ± SEM; n = 4/dose. PE-induced hypertensive responses differed significantly from controls (***p < 0.005) and from one another (++p < 0.01 compared with the moderate dose). Thesolid bar below the curves represents the 25 min duration of drug or vehicle infusion. The pronounced changes in baroreflex indices are assumed to be indicative of rapid resetting of baroreceptor sensitivity in response to a conditioning pressure ramp.