Variability in the preventive action of the B-blockers on genetic hypertension in the rat.

Changes in arterial blood pressure were compared in young male SHR rats untreated or treated orally with a beta-blocker for 5 days out of 7 from the 5th to 9th week of life. Propranolol, acebutolol and practolol, at a daily dose of 50 mg/kg, prevented the occurrence of hypertension, not only during the 4 weeks of treatment, but also during 6,9 and 11 weeks respectively after cessation of treatment. Alprenolol and metoprolol (50 mg/kg/day) and atenolol (100 mg/kg/day) proved to be active only during the period of treatment, whereas oxprenolol (100 mg/kg/day) was totally inactive. Propranolol and acebutolol were, however, inactive under identical conditions with SHR of the same strain but bred in another laboratory. The physiological difference between the two groups of SHR was confirmed by the fact that the resistance of their erythrocytes to osmotic shock was different. This suggests that all the beta-blockers do not necessarily have the same preventive activity with respect to hypertension in the SHR and that two groups of SHR bred in two different places can be physiologically dissimilar even though they originate from the same strain.