John E. Gadsby

New Perspectives on the Endocrine Regulation of the Rabbit Corpus Luteum

In many species a luteotrophic hormone has been identified which maintains the morphological and functional integrity of the corpus luteum. For example, in large domestic animals and in primates LH is thought to have the preeminent role as the luteotrophic hormone (Hansel et al., 1973; Niswender et al., 1980; Knobil, 1973), and prolactin is recognized as the major luteotrophic hormone in the rat (Rothchild, 1981). However, it has become evident that other hormones can act upon the corpus luteum, and thus potentially have a significant influence upon steroidogenic activity as well as lifespan of the gland. To illustrate this feature, progesterone synthesis can be stimulated in cow and sheep corpora lutea by catecholamines in vitro, and this action, at least in sheep, is directly upon steroidogenic luteal cells (Jordan et al., 1978; Condon and Black, 1976). The ultimate control of steroidogenesis in sheep luteal cells is unclear in view of the recent observation that the large luteal cells, which comprise the major progesterone secretory component of the ovine corpus luteum in vivo, exhibit no steroidogenic response either to LH or to elevated cyclic AMP (Fitz et al., 1982; Hoyer et al., 1983). The rat corpus luteum passes through an LH-sensitive period which is thought to be mediated by estrogen produced within the corpus luteum (Gibori et al., 1977; 1978). In the rabbit, 17β-estradiol of follicular origin is considered the essential luteotrophic hormone (Keyes et al., 1983), although the luteal tissue is clearly responsive to LH (Dorrington and Kilpatrick, 1969; Hunzicker-Dunn and Birnbaumer, 1976) and also possesses a catecholamine sensitive adenylyl cyclase (Hunzicker-Dunn, 1982).