Comparative studies on the electric nature of amphibian gonadotropin

The isoelectric focusing (IEF) profiles of pituitary gonadotropic (GTH) activity in six species of adult male amphibians were examined in addition to the newt and bullfrog. The GTH activity was measured by two radioreceptor assay (RRA) systems; one with Xenopus laevis testicular homogenate as the receptor preparation, and the other with Anolis carolinensis testicular homogenate, both employing 125I-labeled rat FSH as the radioligand, or by a radioimmunoassay (RIA) system for bullfrog basic GTH (LH). The IEF profiles were classified into four groups: (1) Cynops pyrrhogaster pyrrhogaster, Onychodactylus japonicus, (2) X. laevis, (3) Rana japonica, Bufo japonicus formosus, (4) Rana nigromaculata, Hyla arborea japonica, Rana catesbeiana. In Onychodactylus japonicus (Group 1), Anolis RRA-positive peaks and Xenopus RRA-positive peaks were found in almost the same fractions. They were in the alkaline to neutral pH region. This IEF profile was very similar to that of newt pituitary GTH in July when spermatogenesis was active. In X. laevis (Group 2), the IEF profile was similar to that of urodeles. However, the most alkaline peak was found at pH 9.02, which was lower than those of urodeles. These peaks showed some differences in the reactivity to the RRA systems. In R. japonica (Group 3), the major peak obtained by Xenopus RRA was found at pH 10.27, which corresponded to the only positive peak obtained by the RIA system for bullfrog basic GTH. Furthermore, this peak was also recognized by Anolis RRA as one of the eight peaks, which appeared in the alkaline to acidic region. In B. japonicus formosus (Group 3), similar results were observed. In H. arborea japonica, R. nigromaculata and R. catesbeiana (Group 4), Anolis RRA-positive and Xenopus RRA-positive peaks were quite independent, indicating distinct separation of LH and FSH, though pIs of FSH-like GTH in the frogs were not so acidic as those of mammalian and avian FSH.