Biological and Immunological Potencies of Lutropin (LH) in Human Serum: Comparative Studies Using Different Standard Preparations

Summary

The mouse Leydig cell in vitro bioassay for LH, first reported by van Damme, Robertson and Diczfalusy (1974) was modified and applied to female and male serum. Non-parallelism of dose-response curves between serial dilutions of individual male as well as female sera and LH standards was caused by damage to incubated interstitial cells in the presence of human serum. The extent of cell damage - paralleled by an inhibition of testosterone production - was a characteristic of individual human sera rather than a general protein effect. This inhibition could be completely avoided by mild heating of the serum for 15 min at 50°C prior to the assay. Using this pretreatment, reliable LH values were obtained for normal males, cycling females and postmenopausal women. Biological LH measurements were compared with RIA-LH potencies. The following LH values were obtained by both methods (mean ± sd) in terms of mIU 2nd IRP HMG/ml serum: males (n = 35), BIO: 23.3 ± 9.0, IMMUNO: 11.0 ± 4.3; cycling females (n = 30), BIO: 30.9 ± 14.6, IMMUNO: 17.4 ± 5.9; postmenopausal women (n = 12), BIO: 324 ± 138, IMMUNO: 117 ± 43. It could be shown that the use of different reference preparations caused great differences in the ratios of biological to immunological potencies e.g. for male serum 0.9-6.9, female serum 0.7-5.6 and post-menopausal female serum 1.1-8.8. Irrespective of the standard used, significant differences between the B:I ratios of male, female and postmenopausal female sera were found.

Key-Words:

Human Lutropin (LH) - In Vitro Bioassay - Interfering Serum Factor(s) - Reference Preparations - Biological vs. Immunological Activity