Microdialysis of melatonin in the confluens sinuum of the rat following quantification by gas chromatography-mass spectrometry in the negative chemical ion mode

In this study, an original surgical implantation technique in the confluens sinuum via the superior sagittal vein was developed to quantify melatonin secretion by the pineal gland. Melatonin (CAS 73-31-4) was determined using gas chromatography couples to negative ion chemical ionisation mass spectr ometry following liquid extraction and derivatisation by pentafluoropropion ic acid anhydride (PFPA). The minimum detectable amount was 40 fg per injec tion, corresponding to 1 pg.ml(-1) in dialysate. The assay was linear in th e range 20-1000 pg.ml(-1). This method was suitable for routine melatonin d etermination in dialysats of peripheral and central circulation with coeffi cients of variation of 11.2 and 24.6%, respectively for within and between analyses. Profiles of melatonin concentration were obtained (n = 3 rats) ov er a 2-day experimentation with a slowly diminution of the filtration capac ity of the probe during the second day. The nocturnal concentrations of mel atonin in the confluens sinuum dialysat ranged from 1003.9 to 2345 pg.ml(-1 ) in the dialysat, indicating wide interindividual variations in the melato nin levels.