Withdrawal syndrome follows abrupt cessation of intracerebroventricular infusion of epinephrine in spontaneously hypertensive rats

Aortic blood pressure and heart rate were measured directly during chronic (5-day) intracerebroventricular infusion of epinephrine in conscious, unrestrained spontaneously hypertensive rats (SHR), and following abrupt cessation of drug infusion. During the infusion period, no statistically significant differences in mean aortic pressures were observed between SHR that received vehicle and those which received epinephrine at 1.25, 2.5, or 5.0 micrograms (base) per hour for 5 days via osmotic minipumps. A significant reduction in heart rate was noted during some, but not all, days of the epinephrine infusion period; the onset of bradycardia appeared to be dose-related. Immediately following abrupt cessation of epinephrine (but not vehicle) infusion, a complex withdrawal syndrome was observed to include: a significant and sustained elevation of aortic blood pressure, tachycardia, increased water consumption, and several distinct behavioral effects. The reaction appeared maximal at about 2 hours, and lasted less than 24 hours.