Effect of an Ectopic Pituitary Gland on Luteal Maintenance in the Hamster

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Abstract
Luteotropic activity in the hamster was studied by transplanting single anterior pituitary glands from cycling or pseudopregnant donors to the kidneys of cyclic recipients. Luteal status was assessed by ovarian histology and decidual cell response (DCR). In hamsters transplanted with pituitaries from donors at similar stages of the estrous cycle, the length of the first cycle was prolonged to 8 days in only a few day 1 and 2 recipients. Pituitaries of pseudopregnant animals on days 3 or 4 consistently induced pseudopregnancy in day 1 recipients. Pituitaries from cyclic animals on day 3 or 4 were also effective in inducing pseudopregnancy in day 1 recipients. Corpora lutea normally begin to regress on day 3 of the cycle; it is therefore understandable why pseudopregnancy could not be elicited in day 3 or 4 recipients. Succeeding cycles were invariably pseudopregnant in type (8-10 days in duration) in all recipients. To determine the mechanism involved in recurrent pseudo-pregnancies, hypophysectomies followed by replacement therapy were performed on pseudopregnant or pregnant animals bearing ectopic pituitaries or lacking transplants. After hypophysectomy in animals without ectopic pituitaries, only replacement with a combination of FSH [follicle-stimulating hormone] and prolactin was able to maintain pregnancy. In animals with ectopic pituitaries after hypophysectomy, only FSH replacement was needed to elicit a DCR or maintain pregnancy. These results indicate that the functional corpus luteum in pregnant or pseudopregnant hamsters is dependent on a minimal complement of FSH and prolactin. The ectopic pituitary induces pseudopregnancy in cycling hamsters by providing the prolactin component.

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