A Comparative Study of the Lipolytic Activity of Thyroid-stimulating Hormone and Luteinizing Hormone

Abstract

Abstract The lipolytic activity of bovine thyroid-stimulating hormone and its subunits have been compared to the lipolytic activity of ovine-luteinizing hormone and its subunits. When tested on white adipocytes isolated from epididymal fat pads of BALB/c mice, thyroid-stimulating hormone was a potent lipolytic agent, active at a concentration of 7 x 10-10 m. In contrast, the isolated subunits of thyroid-stimulating hormone were free of lipolytic activity from 7 x 10-10 m to 4 x 10-7 m. When recombined, 20% of the biological activity of native thyroid-stimulating hormone was regained, indicating that cooperation between the two subunits of thyroid-stimulating hormone is needed to get maximal biological activity. In white adipocytes isolated from epididymal fat pads of rats, thyroid-stimulating hormone was 7 times less active. Treatment by dexamethasone of intact or hypophysectomized rats induced an increased sensitivity to the lipolytic activity of thyroid-stimulating hormone in the adipocytes isolated from epididymal fat pads of these rats. Our data are interpreted to indicate that glucocorticoids are involved in the control of one of the components of the effector system for thyroid stimulating hormone. When the lipolytic activity of bovine- and ovine-luteinizing hormone was tested on the white adipocytes isolated from epididymal fat pads of mice, BALB/c, it was 1000 times less active in comparison with thyroid-stimulating hormone. As reported earlier (Gospodarowicz, D. (1971) Endocrinology 89, 699), all of the biological activity was concentrated in the α chain, and the β chain was free of activity. Our results tend to indicate that the lipolytic activity of luteinizing hormone may be a residual thyroid stimulating hormone activity due to the sharing of common determinants (mainly the α chain).