Summary
This study was prompted by the initial observation of Steelman and Pohley [Endocrinology 53, 604 (1953)] that the dose-response curve was restricted to a narrow range of FSH standard and furthermore that at levels above 0.3 mg FSH (Armour standard 264-151-X of porcine origin) the curve begins to plateau. Later, indications of a similar plateau effect using NIH-FSH-(S1, S2, S3 and S8) all of ovine origin were noted (2–4). In this report optimal conditions for routine bioassay of FSH are presented. Separate site injections of NIH-FSH-S9 (90 and 180 μg) augmented with 40 IU hCG twice daily for 3 days yields a dose-response curve of satisfactory slope for bioassay. The validity and extent of the plateau effect in ovarian response to 180–1000 μg NIH-FSH-S9 augmented with 20, 40, 60 and 80 IU hCG are clearly illustrated. The possibility remains feasible that the plateau and apparent suppression of ovarian response to high FSH concentrations “may” be related to either the biological half-life of FSH in the plasma and/or negative feedback by gonadal steroid hormones.
