Evaluation of a Rat Testis Homogenate Radioligand Receptor Assay for Human Pituitary LH1

Abstract

A rat testis homogenate radioligand receptor assay (RTH-RLA) has been characterized with respect to its usefulness for measurement of LH activity in fractions derived from human pituitary glands. The precision of the RTH-RLA appears adequate as judged by standard statistical analysis of inter- and intra-assay variations in response. The accuracy and specificity of the RTHRLA was determined by measurement of hLH activity in a variety of human pituitary fractions having widely divergent contents of LH, FSH and TSH, and comparison of these results with those obtained using the ovarian ascorbic acid depletion (OAAD) and ventral prostate growth (VPW) bioassays. LER-907 was the reference preparation for all assays used in these comparisons. However LER-907, the 2nd IRP-HMG and the 2nd IS-hCG all gave parallel inhibition curves in the RTHRLA. The mean index of discrimination (ID) RLA/OAAD for measurement of LH content in 20 human pituitary glycoprotein hormone preparations was 1.29. The mean ID RLA/VPW for 8 similar preparations was 3.09. The order of activity found among the various fractions however was similar in each assay system. An exception was desialylated hLH, which showed a significantly higher activity in RLA than OAAD or VPW. This emphasizes that the RTH-RLA is a measurement of hormone binding rather than in vivo biologic activity. The variations in ID and relative potency estimates are explained on the basis of factors affecting the plasma survival time of hLH and the relative importance of these in the dynamics of the chronic (VPA) compared to the acute (OAAD) in vivo bioassays. Our conclusion is that the RTH-RLA can be used to measure hLH activity in pituitary fractions provided the interpretive caveats mentioned above, are kept in mind. (Endocrinology91: 901, 1972)