The three-phase response of urinary serotonin and dopamine in subjects simultaneously taking amino acid precursors of serotonin and dopamine has been defined.1,2 No model exists regarding the renal etiology of the three-phase response. This writing outlines a model explaining the origin of the three-phase response of urinary serotonin and dopamine. A "dual-gate lumen transporter model" for the basolateral monoamine transporters of the kidneys is proposed as being the etiology of the three-phase urinary serotonin and dopamine responses.
Hinz, M., Uncini, T., & Stein, A. (2010). The dual-gate lumen model of renal monoamine transport. Neuropsychiatric Disease and Treatment, 387. https://doi.org/10.2147/ndt.s11704