Rapid distribution of tryptophol (3-indole ethanol) to the brain and other tissues

Tryptophol (3-indole ethanol) is a compound which induces sleep, and is formed: (a) in the liver after disulfiram treatment, and (b) by the parasite in trypanosomal sleeping sickness. We prepared, purified, and characterized radiolabeled tryptophol for the purpose of defining its tissue distribution in animals. Tryptophol was found to be highly lipophilic, with an octanol:water partition coefficient of 29.8. Brain extraction, determined after intracarotid injection, was high (brain uptake index = 117 +/- 3.5%), and nonsaturable, suggesting the absence of a carrier system. After intravenous administration, tryptophol distribution to tissues correlated with relative blood flow. More than 85% of the radioactivity remaining in brain 2-5 min after intravenous injection co-migrated with tryptophol standards when analyzed by thin-layer chromatography. Other evidence suggested that tryptophol binds to serum and in vivo may be stripped from serum albumin and taken up by brain in a single capillary transit. Our study suggests that in states such as trypanosomal sleeping sickness or disulfiram treatment, remotely formed tryptophol gains ready access to brain (it is 100% cleared in a single capillary passage), and could thus cause somnolence.