Direct demonstration of intrinsic follicle-stimulating hormone receptor-binding activity in acid-treated equine luteinizing hormone.
After dissociating equine gonadotropins as a function of time at pH 3, we examined them by radioligand assay and sodium dodecyl sulfate polyacrylamide gel electrophoresis under nondissociating conditions (low, 0.1% SDS). Equine follicle-stimulating hormone (FSH) rapidly lost its receptor-binding activity, and low SDS-polyacrylamide gels demonstrated dissociation into subunits. Maximum dissociation occurred after 20-30 min of pH 3 incubation. Equine luteinizing hormone (LH), however, retained most biologic activity and was largely intact after 72 h of pH 3 incubation. Dose-response curves of acid-treated equine LH and FSH and intact equine LH and FSH were compared in five types of radioligand receptor assays. LH and FSH receptor-binding activities of equine LH were unaffected by pH 3. Equine LH showed 19- and 32-times more activity in the rat testis FSH assay than it did in chicken or horse FSH assays, respectively, directly demonstrating the intrinsic FSH receptor-binding activity of equine LH and the relative lack of specificity for these hormone preparations of the rat FSH receptor. Acid-treated 95% of its biologic activity in FSH assays. In LH assays, the slight (0.2%) activity of equine FSH was relatively unaffected by acid treatment, suggesting that contamination by equine LH accounts for this activity.
D000818:Animals; D002645:Chickens; D004591:Electrophoresis, Polyacrylamide Gel; D005640:Follicle Stimulating Hormone / Q000032:analysis* / Q000378:metabolism; D006736:Horses / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007986:Luteinizing Hormone / Q000032:analysis*; D008297:Male; D011869:Radioligand Assay; D051381:Rats; D011956:Receptors, Cell Surface / Q000378:metabolism; D011962:Receptors, FSH; D013737:Testis
D011956:Receptors, Cell Surface; D011962:Receptors, FSH; D007986:Luteinizing Hormone; D005640:Follicle Stimulating Hormone