β ₂‐ADRENOCEPTORS REGULATE INDUCTION OF MYOCARDIAL ORNITHINE DECARBOXYLASE IN MICE in vivo

The pharmacological characteristics of the myocardial adrenoceptor of the mouse have been examined during embryogenesis by measuring ornithine decarboxylase (ODC, EC 4.1.1.17) induction. A four fold elevation of ODC activity was observed after isoprenaline (10 mg/kg, s.c), and enzyme activity was increased two to three fold following adrenaline (1 mg/kg, s.c.) or terbutaline given by direct injection to the foetus (10 μg/500 mg). Pretreatment with the β‐adrenoceptor antagonist, propranolol (10 mg/kg), totally blocked the increase in ODC activity. Elevation of myocardial ODC activity was not inhibited by metoprolol, a relatively specific β₁‐adrenoceptor antagonist, at a dose of 10 mg/kg. Since the increase in ODC activity was blocked by a β‐adrenoceptor antagonist (propranolol) and enzyme activity was stimulated by terbutaline, a β₂‐agonist, we conclude that β₂‐adrenoceptors are selectively coupled to the regulation of murine cardiac ODC activity following catecholamine stimulation. 1982 British Pharmacological Society