Effect of tissue norepinephrine depletion by 6-hydroxydopamine on blood pressure in spontaneously hypertensive rats

Blood pressure was studied in normotensive and spontaneously hypertensive rats (SHR) in which catecholamine depletion had been produced by 6-hydroxydopamine. After i.v. administration of 80–200 mg/kg 6-hydroxydopamine, norepinephrine (NE) levels in heart, spleen, and kidney were markedly reduced (14–66% of control value) while brain NE remained unchanged. These doses did not affect development of hypertension in SHR or the blood pressure in normotensive control rats during a 20 day period of study. A transient decrease of blood pressure was observed acutely (1–3 days) after an 80 mg/kg dose in normotensive and hypertensive animals. Depletion of NE in the brainstem (to 33–42% of control value) after intraventricular injection of 6-hydroxydopamine, 50–300 μg, had no effect on blood pressure of SHR and normotensive rats. It is concluded that only a small portion of tissue NE content is sufficient for development and maintenance of hypertension in the SHR.