Pharmacokinetics of melatonin in healthy rats and rats with adjuvant arthritis

Objective: To establish a high performance liquid chromatography(HPLC) method for analyzing the concentration of melatonin(MT) in plasma,and to compare the pharmacokinetic parameters of melatonin after intragastric(ig) MT in healthy rats and rats with adjuvant arthritis(AA).Methods: Plasma samples were collected at various time points to measure MT after ig administration of MT in healthy and AA rats.The pharmacokinetic profiles were analyzed by plotting drug concentration versus time.Results: The pharmacokinetics after ig MT inrats was fitted to non-linear pharmacokinetics.As compared with healthy rats,the maximum concentration(Cmax),area under the curve(AUC) and mean residence time(MRT) were significantly increased at low and moderate doses of ig MT(10 and 100 μg·kg-1) in rats with AA;the Tmax,CL/F and Vss/F were significantly decreased;the Cmax and t1/2 were further increased at high dose(1 000 μg·kg-1),while the Tmax,Vss/F,AUC and MRT were significantly decreased.Conclusion:Rate of absorption,total amount of absorption and MRT are increased after ig MT at 10 and 100 μg·kg-1;while total amount of absorption and MRT are decreased at 1 000 μg·kg-1 in rats with AA.