Selective beta-adrenoceptor antagonism of induced formation of 14C-N-acetylserotonin in rat pineal glands in organ culture.

Stimulation of β-adrenoceptors in cultured rat pineal glands increased the formation of (¹⁴C)-N-acetylserotonin (NAcS) from (¹⁴C)-serotonin. The non-selective β-adrenoceptor antagonist dl-propranolol and the selective β₁-adrenoceptor antagonist practolol both decreased the response to the directly acting β-agonist terbutaline 2×10^?4 M, when measured as the amount of (¹⁴C)-NAcS released into culture medium during a 24 h period. A 1,000 times higher concentration was required in the medium using practolol than propranolol to decrease (¹⁴C)-NAcS formation 50% as compared to the level reached using terbutaline 2×10^?4 M by itself.Two different selective β₂-adrenoceptor antagonists were tried: butoxamine (0.05 mM–0.10 mM) and H 35/25 (0.01 mM–0.25 mM). Butoxamine was without effect in the concentrations tested and H 35/25 either did not affect or in the lowest concentration potentiated terbutaline induced (¹⁴C)-NAcS formation. The results indicate that the rat pineal gland β-adrenoceptors studied in organ culture respond similar to the β₁-adrenoceptor subgroup.