Estrogen Action in the Corpus Luteum

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Abstract
The search for unifying concepts and mechanisms concerning the hormonal regulation of the corpus luteum has been frustrated by the numerous reports of marked species differences in requirements for luteotropic hormones. Astwood’s (1) observation that prolactin is luteotropic in the rat has been confirmed by many but a primary luteotropic role for prolactin in other species has not been found. Instead, LH seems to have a primary role (e.g., in the human female, 2) and in some species estradiol is luteotropic (3,4). To add a further disquieting note, it remains a mystery how the gonadotropic hormones maintain both steroidogenesis and cellular morphology. Prolactin is recognized for its luteotropic action in the rat (5), but the cellular mechanism of action is unknown. Rat luteal cells have LH receptors (6) and the corpora lutea are LH-dependent for several days during pregnancy (7,8), yet the respective roles of LH and prolactin in the regulation of the corpus luteum have not been defined. In those species in which estrogen is thought to act on the corpus luteum, the mechanism is unknown and the role of pituitary gonadotropic hormones is a matter of speculation. The research reported here will add some new ingredients to the ferment of research on the corpus luteum, in the hope that a fruitful new avenue of research might be realized and pursued.