The effects of acute and chronic beta-adrenoceptor blockade on the myofibrillar contractile system in the dog heart.

Electrophoretic and enzyme techniques have been used to study the structure and function of the contractile protein system in the myocardium of dogs before and after beta-adrenoceptor blockade. Animals were examined after acute beta-adrenoceptor blockade by using intravenous atenolol (0.2 mg/kg) and following chronic therapy with oral atenolol (100 mg twice daily) for a mean period of 106 days. Two-dimensional polyacrylamide-gel electrophoretic techniques were used to examine the myocardial contractile and regulatory proteins present in endomyocardial biopsy specimens obtained after acute and chronic beta-adrenoceptor blockade. No differences in charge, molecular weight or the relative proportions of actin, myosin light chains, tropomyosin or troponin-C were seen after either acute or chronic beta-adrenoceptor blockade. The maximal activity and calcium sensitivity of the myofibrillar adenosine triphosphatase (ATPase) was also unchanged after acute and chronic atenolol therapy. It is concluded that beta-adrenoceptor blockade has no significant adaptive effect on the structural or functional properties of the myofibril.