Figure 2. Maximum evoked change in blood pressure (expressed as the mean +/- SEM) as a percentage of the change in blood pressure measured before drug injection at time zero. The response at each time point was evoked by compressing the knee joint to 200 mmHg for 2 min in rats that received an intraarticular injection of kaolin and carrageenan 3.5 hr before treatment. The bottom panel indicates the control response associated with kaolin and carrageenan alone (IA CAR) or carrageenan plus intraarticular saline at time zero. The top two panels show the effects of U-50,488H (3 mg, middle) or morphine (3 mg, top) given at time zero. Because the intraarticular injection alone exaggerates the response, all intramuscular injections of drug were accompanied by a concurrent injection of saline into the knee joint (e.g., intraarticular saline). Each line presents the mean +/- SEM of four to eight rats.