Lack of effect of increased pineal serotonin content on H3-tryptophan uptake

Major increases in the serotonin concentrations of rat pineal organs were produced by administering Catron, a monoamine oxidase inhibitor, prior to autopsy, or by preincubating the glands with serotonin (3X10-4M). These increases had no effect on pineal uptake of H3-tryptophan, the amino acid precursor for serotonin. These observations provide further evidence that the control of serotonin synthesis involves an important "open-loop" component.