Molecular composition of two different batches of urofollitropin: analysis by immunofluorimetric assay, radioligand receptor assay and in vitro bioassay.

The molecular heterogeneity of two different batches of commercially available urofolitropin was analyzed after fractionation by isoelectric focusing (IEF). FSH was measured before and after IEF by a highly specific time-resolved immunofluorimetric assay (IFMA), by a radioligand receptor assay (RRA) employing a preparation of calf testis FSH receptors, and by the in vitro bioassay based on FSH-dependent aromatase stimulation in immature rat Sertoli cells. An overall good correspondence between the results obtained with the three different methods was observed. However, the RRA and the in vitro bioassay appeared to be more suitable than the IFMA in resolving individual FSH isoforms. The mean isoelectric points of the two FSH preparations analyzed were slightly different, due to different molecular composition. These differences, however, seem too minute to be considered as cause of the different pharmacokinetics of FSH described in the literature or to explain the inconsistent therapeutical results seen in patients treated with FSH of urinary origin.