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Different profiles of isoelectric avian luteinizing hormone components in biological activity and immunoreactivity
Abstract:
Chicken LH components from the glycoprotein fraction of the anterior pituitary glands have been separated to isoelectric homogeneity by means of isoelectric focusing, and investigated for their biological activities in vitro. The activities of these components were measured with LH receptor binding, cyclic AMP accumulation and testosterone production in rat Leydig cells at equal doses expressed as immunoreactivity of IRC-2 (Gunma). All the components were active in the heterologous assay systems, although the relative potency expressed as the ratios of biological activity to immunoreactivity (B:I) differed significantly among the components. Component I, the amount of which is the largest (40-50%), with the most alkaline isoelectric point (pI) showed the highest B:I ratio, and the B:I ratio decreased with decreasing pI in the same way as in rat LH components (Wakabayashi, 1980; Hattori et al., 1983). Therefore, pituitary LH from photostimulated male quail, where the relative amount of component I was increased, was estimated to have higher B:I ratios than that from short-day (SD) treated male quail. Furthermore, the differences in activities among the components obtained by the three assays were in the following order: testosterone production greater than cyclic AMP accumulation greater than receptor binding, suggesting that the hormonal actions of components with higher B:I ratios (I, II and III) are efficiently amplified in the biological response to the final step. In the incubation of pituitary glands with hypothalamic extracts, component I in the pituitary glands from the long-day (LD) treated group was mostly decreased after the incubation, while all the components were decreased in parallel in the SD-treated group. The results suggest that the LH component releasable to GnRH changes in endocrine status though component I with the highest B:I ratio is relatively releasable in both SD- and LD-treated groups.