Measurement of melatonin in blood by radioimmunoassay. Analytical considerations and clinical usefulness

Graphene and Co-polymer composite based molecularly imprinted sensor for ultratrace determination of melatonin in human biological fluids

A novel molecularly imprinted polymer (MIP) sensor based on a composite of graphene (GR) and a co-polymer of 4-amino-3-hydroxy-1-naphthalenesulfonic acid (AHNSA) and melamine (MM) has been fabricated for detecting melatonin.

An ultra-high sensitive bioanalytical method for plasma melatonin by liquid chromatography-tandem mass spectrometry using water as calibration matrix

For the endogenous substances with an ultra-low level in biological fluids, such as melatonin, the blank biological matrix is obviously not "blank". This problem leads to a serious issue of the bioanalytical methods development and validation by liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS). This work developed and validated an ultra-high sensitive bioanalytical method for plasma melatonin by LC-MS/MS using water as calibration matrix. The lower limit of quantitation of the method was verified to be 1.0 pg/mL and the method exhibited a linear range of 1-5000 pg/mL. Potential matrix effects, accuracy and precision were fully monitored and validated by two complementary quality control approaches respectively using water and the pooled plasma as matrix. The intra-run and inter-run precisions were less than 11.5% and 12.2%, respectively, and the relative error was below ± 13.8% for all of 5 quality control levels. The method was successfully applied to investigate the daytime (8:00 AM-8:00 PM) baseline level of endogenous plasma melatonin, as well as the pharmacokinetic profiles of exogenous melatonin after oral administration in beagle dogs.

Rapid determination of serum melatonin by ESI-MS-MS with direct sample injection

This paper describes a rapid, simple and sensitive analytical method for the quantitative determination of melatonin in human serum by ESI-MS-MS with direct serum sample injection and on-line extraction. The method uses N-acetyltryptamine as the internal standard. It has high specificity and sensitivity for serum melatonin analysis. The internal calibration curve shows a wide linear range from 0.500 to 200 ng/ml with a correlation coefficient, R(2) > 0.999. The limit of quantitation is 0.500 ng/ml and the limit of detection is 0.100 ng/ml with 10-microl sample injection. The recoveries of serum melatonin at three levels are approximately 70%. The intra-assay precision (n = 5) is between 0.8 and 2.0% and the inter-assay precision (n = 3) is between 1.5 and 5.9% over the calibration range. This method has a total analysis time of less than 9 min. It can be used for the measurement of melatonin in human blood.

Exogenous melatonin entrains rhythm and reduces amplitude of endogenous melatonin: an in vivo microdialysis study

The circadian rhythm of melatonin production was studied using on-line, in vivo microdialysis in the rat pineal gland. With this technique it was possible to record a pronounced melatonin rhythm with very high time resolution. Three phase-markers of the rhythm were calculated from the data, indicating increase (IT50), decrease (DT50) and amplitude of the rhythm. Comparing these phase markers led to several conclusions. Entrainment of the rhythm under constant darkness was performed with melatonin administration at different circadian stages [circadian time (CT) 8 and CT12] and for different periods of time (2 weeks and 4 weeks). Also, entrainment was established by applying 15 min light pulses at CT0. Entrainment of IT50 with melatonin partially uncoupled it from DT50. Four weeks entrainment in constant darkness (DD) caused a phase-delay in DT50 of 2.2 hr. Entrainment of IT50 with light at CT0 for 2 weeks in DD caused a phase-advance in DT50 of 1.3 hr. The entrainment with melatonin was restricted to a narrow window for melatonin to be applied, since injections at CT8 did not result in entrainment. Exogenous melatonin reduced the amplitude of the rhythm of endogenous melatonin. This effect was not circadian time dependent, since administration at CT8 for 2 weeks and at CT12 for 4 weeks resulted in a highly significant decrease. Light did not seem to have an effect on the amplitude. The data presented here provide us with new information about the nature of entrainment by melatonin. Since the present development of melatonergic agents for clinical use focuses on the entrainment capacity, effects of these compounds on amplitude of circadian rhythms needs to be addressed. In vivo microdialysis seems to be a good technique for that.