Fig. 2.

Amphetamine pretreatment elicits hypertensive response sensitization (HTRS). Rats that received a history of amphetamine during induction (IND) exhibited elevated mean arterial pressure (MAP) to a slow-pressor dose of angiotensin II during an expression phase (EXP) displayed in A. Control MAP during recordings 1–5 (B1–B5) was used to assess that MAP was equivalent across groups at baseline. Amphetamine was injected on days 1–7 (IND), and the delay period (DEL) occurred between days 8 and 14. On day 15, EXP began. A significant elevation in MAP in amphetamine-pretreated rats was observed on days 23–25 compared with saline-pretreated rats (*P < 0.05), demonstrating HTRS. Furthermore, MAP was blocked across experiment phases (B). We analyzed the difference between MAP during EXP week 1 and EXP week 2 as we hypothesized MAP would be elevated during EXP. A significant elevation in MAP was found during the 2nd week of EXP (*P < 0.05).