Binding of melatonin to human and rat plasma proteins.

Abstract

3H-Melatonin was not metabolized when incubated with rat venous blood in vitro and 72-82% of the added radioactivity was recovered in the plasma fractions. The binding of 3H-melatonin to rat and human plasma proteins was studied by equilibrium dialysis; there were no significant differences between the binding capacities of human and rat plasma, and the proportions bound (77.8 ± 4.3% and 60.7 ± 4.8% at 4 and 37 C, respectively) were independent of melatonin concentration up to 1.5 HIM, indicating a highcapacity binder protein. The in vitro binding of melatonin to plasma proteins was not modified by the presence of other indole derivatives. Equilibrium dialysis of 3H-melatonin with purified plasma protein fractions and electrophoresis of plasma preincubated with melatonin revealed that albumin was the only melatonin-binding protein detectable in plasma. No significant association was observed between melatonin and macromolecules in fresh cerebrospinal fluid (CSF) from goats unless the protein concentration...