Immunological studies with the gonadotropins and their subunits from the green sea turtle Chelonia mydas

Abstract

Antisera generated in rabbits against highly purified follicle-stimulating hormone (FSH), luteinizing hormone (LH), and the β subunit of LH from the green sea turtle, Chelonia mydas, were used to obtain additional biochemical information on the chemical and biological relatedness between the two turtle gonadotropins. Evidence that the antisera were directed against the biologically active gonadotropins was obtained from neutralization studies. At concentrations of 1 ml of antiserum per 100 μg of hormone, FSH and LH could each be selectively neutralized with homologous antisera. These results provide additional evidence that both gonadotropins have intrinsic biological activities in assays related to testis growth and androgen production in lizards and in vitro androgen production by snake testes. Each antiserum ( a s ) showed some binding to the heterologous radioiodinated hormone, but binding was clearly maximal with homologous tracer, and some of this cross-reaction was shown to be due to heterogeneity in antibody populations. Highly specific radioimmunoassays (RIAs) were developed for both FSH and LH with these antisera. When FSH a s was used in conjunction with 125I-labeled FSH, Chelonia LH and thyroid-stimulating hormone (TSH) showing virtually no cross-reaction (e.g., contamination of LH with FSH was < 1%). Alternatively, RIA using either LHβ a s or LH a s combined with 125I-labeled LHβ as tracer was highly specific for LH and especially the β subunit; there was no cross-reaction with either FSH, TSH, or the α subunit of LH. When LH a s was used with 125I-labeled α as tracer, the specificity of the RIA was reduced; in this case, LHβ alone showed no cross-reaction but LHα was highly potent. Thus, these systems provide a means for studying the importance of the two separate subunits in immunorelatedness among pituitary glycoprotein hormones and for measurement of circulating gonadotropin levels.