Therapeutic preparations of FSH, used primarily for treatment of infertility, are calibrated by in vivo bioassay against international standards (IS) derived from different sources deemed appropriate to their use according to pharmacopoeial monographs. Menotrophins, which have been used for several decades to treat infertility, have been calibrated against the IS for urinary FSH and LH (ISU) but are now being replaced by highly purified urinary FSH or rDNA-derived FSH (rFSH).The aim of this study was to evaluate two preparations of human rFSH and one preparation of highly purified urinary FSH as candidate WHO IS for bioassay in an international collaborative study by 27 laboratories in 12 countries, and to characterise them in a range of in vitro bioassays and immunoassays.The biological activity of the three candidate standards was confirmed by all laboratories using all assays contributed to the study. Dose-response relationships by in vivo bioassay for any of the candidate standards did not differ significantly from that for the ISU. Dose-response relationships obtained in in vitro bioassays and immunoassays were also broadly similar among these preparations although dose-response lines for some preparations appeared to be non-parallel in some immunoassays. For each of the three candidate IS, estimates of the relative potency in terms of ISU by in vivo bioassay did not differ significantly between laboratories. In contrast estimates by immunoassays and in vitro bioassays showed significant differences between laboratories. Estimates of relative potency of the highly purified candidate IS materials in terms of one another exhibited less inter-laboratory variability than estimates in terms of ISU. Each of the candidate standards showed adequate stability to serve as an IS.On the basis of the results of this study rFSH (code 92/642) was established as the first IS for FSH, human, recombinant for bioassay with an assigned unitage of 138 IU per ampoule and urinary FSH (code 92/512) was established as the first IS for FSH, human, urinary (urofollitropin) for bioassay with an assigned unitage of 121 IU per ampoule, based on their respective calibration by in vivo bioassay in terms of ISU. These assignments of unitage maintain continuity of unitage for preparations in therapeutic use and also appear to be consistent with one another.

Dear Sir,We read with concern the article by Parte and Juneja (Assessment of Bioactivity of WHO/NIH Research Standard for Inhibin [code 86/690] using two separate pituitary cell culture systems. Parte, P. P. and Juneja, H. H, Horm. Metab. Res. 25: 356-359 [1993]). As distributors of this standard, we wish to make the following comments:The preparation of porcine inhibin ampouled in 1986 under code number 86/690, was intended to serve as an internationally available interim research standard for in vitro bioassays pending the availability of more suitable highly purified material, ideally recombinant human inhibin, in sufficient quantity for ampouling. This research standard was initially assessed for bioactivity in a number of independent expert laboratories involved in the characterisation of inhibin at that time. In the interests of making a research standard for in vitro bioassay available on a world wide basis as quickly as possible, the results of that study were published in 1987. It is significant that Parte and Juneja do not cite that reference (Waites, Bialy, Gordon, Findlay, de Jong, Robertson, Schwartz and Storring 1987).A formal international collaborative study under the auspices of the World Health Organization was initiated in 1988, this time with ten independent expert laboratories in eight countries and again assessing the biological activity of 86/690 with a number of other ampouled or local preparations of different inhibins in in vitro bioassays. A detailed report of that study was drafted in 1990 and circulated to all the participants (who included scientists from the same address as Parte and Juneja) to invite their comments. The assigned potency of 2000 International Units (to maintain continuity with the biological potency originally adopted for its research use) was agreed by the participants who recommended to the WHO Expert Committee on Biological Standardisation that ampoule code 86/690 appeared suitable to serve as a biological standard for in vitro bioassay. The publication of the report of that international collaborative study appeared in Journal of Reproduction and Fertility in 1992 (Gaines-Das, Rose and Zanelli 1992) -again, Parte and Juneja do not cite that reference.It is clear that the experimental data presented by Parte and Juneja do not include a positive control such as a test of the responsiveness of their two pituitary cell systems to inhibins other than 86/690 (eg recombinant human inhibin which is now available). The preparation of porcine inhibin in 86/690 was well described in 1987 as being of 1 -3 % purity and of course the possibility of other active components cannot be excluded as discussed further in reference (Gaines-Das, Rose and Zanelli 1992). Nevertheless, this preparation appears to have served the scientific research community well since 1987; some 300 ampoules have been distributed and, to our knowledge, the report by Parte and Juneja is the first to suggest that the preparation does not show a dose dependent inhibition of basal FSH release in a pituitar...