Effects of norepinephrine on pineal tryptophan hydroxylase, using an improved [14C]CO2-trapping microtechnique

Measurement of tryptophan hydroxylase activity in rat pineal glands and pinealocytes using an HPLC assay with electrochemical detection

A method for measuring tryptophan hydroxylase activity by assaying the product 5-HTP using high-performance liquid chromatography (HPLC) with electrochemical detection is described. A nocturnal elevation (80%) in rat pineal gland tryptophan hydroxylase activity was detected. Experiments on isolated rat pinealocytes with the protein synthesis inhibitor cycloheximide indicate that tryptophan hydroxylase turns over rapidly in these cells. This method will be valuable in studies of the adrenergic mechanisms regulating pineal tryptophan hydroxylase activity.

Effect of oxygen on the induction of tryptophan hydroxylase by adrenergic agents in organ cultures of rat pineal glands

Rat pineal glands, cultured under 95% air and 5% CO2, lost 50% of their tryptophan hydroxylase activity within 5 h. This loss was accelerated by the addition of cycloheximide or puromycin to the medium. Activity was, however, largely maintained in 95% O2 and 5% CO2. Under these conditions, L-noradrenaline (100 microM), L-isoproterenol (10 microM), and dibutyryl cyclic AMP (1 mM) induced enzyme activity. They failed to do so when 95% air and 5% CO2 was used. Noradrenaline induced serotonin N-acetyltransferase activity with either atmosphere.

Diurnal variation in the serotonin content and turnover in the pineal gland of the Syrian hamster

Serotonin and 5-hydroxyindoleacetic acid were measured in the pineal gland of Syrian hamsters by high performance liquid chromatography over a period of 24 h. A distinct 24 h rhythm was detected for both indoles. Turnover studies revealed a higher rate of serotonin synthesis during the day than during the night. We therefore suggest that the serotonin content in the pineal gland of the Syrian hamster is regulated by changes in its synthesis rate, rather than by changes of serotonin catabolism, via N-acetyltransferase activity.