Enhancement of hydroxyindole-O-methyltransferase and DNA-dependent RNA polymerase activities induced by oestradiol in rat pineals in culture.

1. Hydroxyindole-O-methyltransferase and DNA-dependent RNA polymerase activities were determined in the pineal gland removed from the ovariectomised rat and cultured under various experimental conditions. 2. The transferase activity declined very slowly during 24 h of incubation. 17beta-Oestradiol significantly increased the transferase activity within 2h after the addition, and the extent of increase was dose-dependent within the concentration range from 0.1 to 15 nM, being increased by 80% at 15 nM. Enhancement of the transferase activity by oestradiol was abolished not only by inhibitors of protein synthesis (cycloheximide and puromycin), but also by those of RNA synthesis (actinomycin D and alpha-amanitin). It was also blocked by clomiphene citrate, an agent which is known to inhibit the binding of steroid hormones to their respective receptors. 3. RNA polymerase activity (forms A and B) declined rapidly during the initial period of pineal culture. Oestradiol (15 nM) increased the RNA polymerase B activity by 50% within 2 h after the addition. The increase was dose-dependent within the concentration range from 0.1 to 15 nM, and was abolished by clomiphene citrate. 4. The possibility is suggested that the pineal is a target organ of oestradiol, and that the steroid-induced reaction sequence in the pineal conforms to that is known in other target organs.