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The Biological Standardisation of Human Growth Hormone (HGH Stroud)
Abstract
Radio-immunological determinations reflect antigenicity but not necessarily biological activity; consequently the purified HGH Stroud extract was calibrated using the tibia test of Evans, as modified by Greenspan et al. This was conducted concurrently with the X-ray plate method of Leget et al. In this way the true dimensions of the tibial epiphyseal slit in vitro could be compared with the in vivo state, obtained by means of X-ray plates. A total of 92 test animals was used. The experimental procedure was aimed at eliminating the rat factor as far as possible, and the 4-point biological calibration method was employed. The first International Standard for bovine growth hormone (BGH), which contains 1 IUjmg, was used as standard, in low and high doses of 15 and 60 ,ug BGH/ml respectively. According to the silver nitrate method the HGH concentration was 3,4 IU/mg of purified extract, whereas with the X-ray plate method this value was 1,9. The corresponding λ-value for the silver nitrate and X-ray plate methods were 0,793 and 0,728. The λ value for the tibia test usually varies between 0,301 and 0,491. The λ values obtained were therefore comparable but disappointingly high for both methods, in spite of all the precautions taken. Calibration according to these two methods also produced divergent results. For the silver nitrate method the 0,95 confidence 'limits fell at 3,0 and 19,6, with a potency of 11 ug standard per ug test sample; for the X-ray plate method the 0,95 confidence limits fell at 1,9 and 102,3, with a potency of 4,9 ug standard per ug of HGH extract. Since the silver nitrate method has been in use longer and is consequently better known, greater value was attached to the potency value obtained by using this method. The average value obtained thus indicated that the HGH extract was about three times as potent physiologically as the International Standard for BGH. It is concluded that the X-ray plate method provides an alternative to the silver nitrate method, one where a permanent record is available and where the test animals need not be sacrificed. Uncertainty still exists concerning the dependability of the X-ray method since a poor correlation was found with the results of the silver nitrate method. No significant contamination with glycoprotein hormones, ACTH, TSH or prolactin, could be demonstrated
