Propranolol in DOCA hypertensive rats: development of hypertension inhibited and pressor responsiveness enhanced.

D,L-Propranolol given in single doses by gavage or s.c. injection to awake rats, always slowed the heart without affecting blood pressure. Doses of 0.2 mg/100 g injected twice daily lowered systolic pressure after 3 days in DOCA hypertensive but not in normotensive or spontaneously hypertensive rats. When chronic treatment with propranolol preceded the induction of DOCA hypertension, the pressure elevation attained 14 weeks later was less in treated than in untreated rats. Pressor responses to injected norepinephrine and to posterior hypothalamic stimulation were significantly larger in DOCA hypertensive rats that had been treated chronically with propranolol than in those that had not. These results suggest that propranolol's antihypertensive effects are unimpressive because they are simultaneously opposed by an enhanced cardiovascular responsiveness to pressor stimuli.