Comparative physiological disposition of melatonin and its benzo(b)thiophene analog in the rat

Melatonin and its benzob]thiophene analog were labeled by acetylation of the corresponding 5-methoxyarylethylamines with ³H-acetic anhydride. The benzob]thiophene analog had a much higher lipid solubility. When administered to rats, both compounds disappeared from plasma and tissues by first-order decay. The dispositions were similar, with the higher lipid solubility of the benzob]thiophene analog resulting in higher tissue: plasma ratios, especially in adipose tissue, kidney and liver, and longer half-lives in plasma and tissues.