VALIDATION OF AN IMPROVED INVITRO BIOASSAY TO MEASURE LH IN DIVERSE SPECIES

Cultured Leydig tumor cells (MA-10) respond to luteinizing hormone (LH ) by synthesizing and secreting progesterone (P). The specificity of t he response to LH prompted us to develop this system for use as a simp le and rapid in vitro bioassay for LH. The aims of this study were to (1) improve sensitivity and reproducibility, and (2) optimize the assa y for use in diverse animal species. A minimum sensitivity was observe d at 0.05 mIU/well of LH with 0.5 x 10(4) cells/well for 1.5 hours. At higher concentrations of LH, shorter incubation periods also signific antly stimulated P production. Addition of human LH standard or serum samples resulted in a dose-dependent increase in P production. Paralle l dose-dependent curves were observed with LH preparations from mammal ian, avian, and amphibian species. In conclusion, these findings demon strate that (1) the assay is rapid, sensitive, and reproducible; (2) s erum LH levels analyzed using this assay and the mouse Leydig cell bio assay are comparable; (3) shorter incubation times suggest the impleme ntation of this assay for rapid qualitative determination of LH surges ; and (4) the assay can be used for the analysis of samples from diver se species, especially those lacking radioimmunoassays. Therefore, thi s assay system allows for the simple and rapid measurement of circulat ing bioactive LH levels in humans and diverse animal species, and shou ld provide insight regarding the role of bioactive LH in physiogical a nd pathological conditions.