An immunological approach to study gonadotropin action at the cellular and molecular level.

The last two decades have seen a rapid development of a variety of new techniques and probes to understand the regulatory functions of hormones. One such tool is antibodies against hormones. Antibodies against the gonadotropins Lutropin (LH) and Follitropin (FSH), in addition to showing hormonal specificity, react with LH and FSH of a variety of other species (1-3). This property has been found extremely useful in developing heterologous radioimmunoassay (RIA) systems (4) and also for neutralizing endogenous LH or FSH at critical periods of reproduction in a variety of animals (5, 6). The classical approach to study the action of gonadotropins has been to use the hypophysectomized animal model and administer as required hormones having LH or FSH activity. Such an approach would result in the removal, at a stroke, of all the pituitary hormones other than the supplemented gonadotropin. In this procedure the permissive or antagonistic effect that the other pituitary hormones may have on the gonadotropin action when animals are in a normal physiological state is mostly overlooked. In contrast, use of an antibody, whose specificity can readily be manipulated, ensures that a physiologically normal animal can be deprived of a single hormone at any given time for a fixed period. This approach has been taken advantage of in elucidating, beyond reasonable doubt, the luteotropic activity o f L H in the cycling and pregnant rat, hamster, ~nonkey and the rabbit (7,8). Use of a specific FSH antibody similarly helped to establish, for the first time, the need for this hormone in maintaining spermatogenesis and fertility in the primate (9-12). Further, specific gonadotropin antibodies have also been employed successfully in studying events like follicular maturation, ovulation, implantation and also as a vaccine to prevent or terminate pregnancy. This aspect has been reviewed in depth earlier (7, 13,14). In the present paper emphasis will be laid on discussing in some depth how specific LH and FSH antibodies have been used to further our knowledge of the mechanism of action of these hormones at the cellular level.