ABSTRACT
Melatonin (MT) is a lipophilic amino acid derivative and is not stored but directly released from the pineal gland by diffusion. About 60%–85% of the circulating MT is bound to albumin [1,2]. MT displays high lipid and water solubility and gains access to various —uids, tissues, and cellular compartments. It is therefore detected in saliva [3], urine [4], cerebrospinal —uid (CSF) [5], semen [6], amniotic —uid [7], and milk [8]. Just like the serum/plasma hormone pro£le, levels of MT likewise display a circadian rhythm in other body —uids. Besides measurements of MT levels in plasma or serum, measurements have also been carried out in all kinds of other body —uids both to monitor the circadian rhythm of MT and to understand the multiple molecular functions of MT, for example, in the ventricular system of the brain. Because the concentrations of proteins and other constituents can vary several folds in body —uids according to the presence of any kind of disease, the sampling time, or methods, the matrix effects of these constituents can be expected to in—uence the measurement of MT.
