A COMPARISON OF HPLC AND BIOASSAY METHODS FOR PLASMA MELANOTAN-II (MT-II) DETERMINATION - APPLICATION TO A PHARMACOKINETIC STUDY IN RATS

The pharmacokinetic profile of the melanotropic peptide, melanotan-II (MT-II), was determined in rats following a 0.3 mg kg(-1) intravenous dose. Regression analysis of the plasma MT-II concentrations determine d using HPLC and bioassay methods indicated the existence of a signifi cant linear correlation (r = 0.90, p<0.001). The plasma concentration versus time plots determined using the two assay methods yielded bipha sic disposition profiles that were essentially superimposable. The fol lowing pharmacokinetic parameters were assessed from plasma concentrat ion versus time data using both methods: C-max, AUC, CL(s), t(1/2 beta ), MRT, V-d beta and V-ss+. Statistical comparison showed that the par ameters measured by each method were not significantly different (at t he 0.05 level) except for t(1/2 beta), MRT and V-ss. The presence of e ven one aberrant data point in the beta-phase can significantly influe nce t(1/2 beta) when only a few data points are available in the beta- phase. Since MRT and V-ss were calculated from t(1/2 beta) it is not s urprising that these two parameters also differed between methods.