Beta 2-mediated hypotension and myocardial injury

This study was designed to investigate the importance of beta 2 receptor mediated hypotension in the pathogenesis of myocardial injury. The effect of isoproterenol and the putative beta 2 agonist albuterol on arterial blood pressure, heart rate, the myocardial content of ATP and cAMP, and the serum content of MB-CPK was examined in conscious rats. Isoproterenol (5.25 mg/kg, s.c.) and albuterol (45 mg/kg, s.c.) lowered blood pressure and elevated heart rate to the same extent. Also, both agonists increased the myocardial content of cAMP, decreased the myocardial content of ATP, and elevated serum MB-CPK. The beta 1 antagonist practolol, but not the ganglionic blocking agent chlorisondamine, attenuated the elevation in heart rate to albuterol without reducing its effect on blood pressure. Practolol, but not chlorisondamine, abolished the effects of albuterol on cAMP, ATP, and MB-CPK. These data suggest that the myocardial injury which is associated with an increased heart rate and changes in cAMP, ATP, and MB-CPK following the administration of albuterol is not the result of beta 2-mediated hypotension, but is due to stimulation of myocardial beta 1 receptors.