THE ASSAY OF HUMAN FOLLICLE-STIMULATING HORMONE PREPARATIONS: THE CHOICE OF A SUITABLE STANDARD

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Abstract
Eleven pituitary or urinary preparations of varying purity were assayed for FSH [follicle stimulating hormone] activity by an in vitro bioassay method, a receptor binding assay (RBA) technique and a radioimmunoassay (RIA) procedure, employing 2 anti-FSH sera with and without absorption with h[human]CG [chorionic gonadotropin]. All methods were specific for hFSH, since other glycoproteins (hFSH.alpha. and hFSH.beta. subunits, hLH [luteinizing hormone], hCG and hTSH [thyrotropin]) elicited little, if any, response. A partially purified hFSH preparation (1st IRP [International Reference Preparations] of human pituitary gonadotropins (FSH and LH) for bioassay, code No. 69/104) was used as standard in all assays. In addition, potency estimates were expressed in terms of a highly purified hFSH preparation (hFSH-Kabi, Lot No. 19344) and in terms of the hMG [menopausal gonadotropin] (2nd IRP). Significant differences in the ratios of biological activity to receptor binding activity (B/R) and to immunological reactivity (B/I) were observed between preparations which were unrelated to their level of purity. The use of the 69/104 preparation as standard gave significantly higher B/R and B/I ratios than the use of the hMG (2nd IRP) and of a highly purified hFSH preparation. In addition, the use of the hMG (2nd IRP) as a standard gave significantly higher B/R ratios than that of the highly purified hFSH preparation. The 69/104 and hMG (2nd IRP) preparations contain significantly more biologically inactive receptor binding material than the more extensively purified hFSH preparation. Furthermore, the 69/104 preparation contains significantly more biologically inactive immunologically reactive material than both hMG reference standards and the highly purified hFSH preparation. Because of the presence in the 69/104 preparation of relatively large quantities of biologically inactive material which behaves in both the RBA and RIA procedures as hFSH, this preparation is not suitable as standard for the quantitation of FSH activity by methods other than bioassays. For the same reason, the relatively crude 2nd IRP (but not its replacement, the 1st IS [International Standard] for human urinary FSH and LH for bioassay) appears to be unsuitable as a standard for the assay of hFSH by RBA procedures. Among the limited number of preparations studied, a highly purified pituitary hFSH preparation appears to be the most satisfactory as a provisional standard for hFSH assays, although even this material contains some biologically inactive hFSH-like material.