Methoxyindole production by the pineal gland appears to be dependent on the concentration of hydroxy precursors and their affinity for hydroxyindole-O-methyltransferase.

Various pineal gland indole metabolites were separated by thin-layer chromatography after organ culture with tritiated serotonin. The amounts of methoxyindoles produced were remarkably constant and female rats in oestrus appeared to produce greater amounts than male rats. The results show a correlation between methylation and the concentration and affinity of the various hydroxyindoles for hydroxyindole-O-methyltransferase.