Alteration of respiratory cycle timing by propranolol

The present study was undertaken to explore the effect of propranolol on respiratory cycle timing and breathing pattern using mice and guinea pigs. Propranolol was administered via aerosol or via injection. Mice exposed to propranolol aerosols exhibited a breathing pattern that was characterized by a pause between breaths. The length of such pauses (TP) increased as the propranolol exposure concentration was raised. We also observed at increasing propranolol concentrations that the time of inspiration (TI) and time of expiration (TE) decreased. Thus, the respiratory rate of these animals was seen to increase, remain unchanged, or decrease depending on the balance between TP versus TI and TE. Guinea pigs also exhibited pauses between breaths during exposure to propranolol aerosols, but such pauses were not observed as consistently as in mice. TP again rose while TI and TE fell in guinea pigs exposed to increasing propranolol concentrations. This species was, however, less sensitive than mice. Intraperitoneal injections of propranolol failed to elicit such alterations in respiratory pattern or timing in either species. These changes in respiratory timing obtained with an aerosol of propranolol were most probably due to a local effect on vagal nerve endings or to its bronchoconstricting effect.