EFFECTS OF PROPRANOLOL AND ATENOLOL ON IMMOBILIZATION STRESS-INDUCED HYPERTENSION AND DOWN-REGULATION OF CENTRAL BETA-ADRENOCEPTORS IN RATS

Effects of chronic treatment with propranolol or atenolol on stress-in duced changes in blood pressure, body weight, and cerebral beta-adreno ceptors in rats were examined and compared with the effects of chronic treatment with prazosin. Immobilization stress (2 h daily for 2 weeks ) induced a moderate elevation of blood pressure, loss of body weight gain, and downregulation of cerebral beta-adrenoceptors, but produced no changes in the cerebral alpha(1)-adrenoceptors. Chronic administrat ion of propranolol (5 or 50 mg.kg(-1)), atenolol (5 or 50 mg.kg-1) or prazosin (2 or 20 mg.kg(-1)) stress-induced hypertension but did not a ffect loss of body weight gain. Propranolol increased the density of c erebral beta-adrenoceptors by 77% and reduced the downregulation induc ed by stress. Atenolol also increased the density of cerebral beta-adr enoceptors by 34% and abolished the stress-induced downregulation in c erebral beta-adrenoceptor density. In contrast, prazosin had no effect on the cerebral beta-adrenoceptors in nonstressed or stressed rats. T hese results suggest that the antihypertensive action of propranolol a nd atenolol may be partly associated with the inhibition of stress-act ivated central beta-adrenoceptor transmission.