Luteotropic complex of the mouse

Abstract

Abstract Pregnant mice were hypophysectomized on day 6 and injected subcutaneously with various hormones from days 6 to 9 to establish the minimal requirements for the maintenance of functional corpora lutea. Luteal activity was assessed by the maintenance of pregnancy, weight of embryonic swellings, mean diameter and morphology of corpora lutea, and vaginal histology. Treatment with 2 mg progesterone maintained pregnancy but not corpora lutea in three of five animals. However, the embryonic swellings were significantly (P < 0.0005) smaller than those of pregnant control animals. Pregnancy was maintained in all animals when progesterone was combined with 1 μg of estrone. The weights of embryonic swellings and the degree of vaginal mucification in the combined steroid group were similar to those of intact control animals. Treatment with either ovine prolactin, bovine LH, ovine FSH or estrone failed to maintain corpora lutea or pregnancy. Combined injection of prolactin with LH or estrone did not maintain pregnancy or corpora lutea. On the other hand, treatment with 500 μg of prolactin and 200 μg of FSH maintained pregnancy in 12 of 14 animals. All of the aforementioned parameters of luteal activity were comparable to values in intact, control animals. The data indicate that luteal function in the mouse during the early post‐implantation period requires a luteotropic complex rather than a single hormone. Prolactin and FSH constitute the minimal luteotropic complex in the pregnant mouse. The luteotropic activity of FSH was not due to its contamination with LH and the effect of FSH was apparently not mediated through estrogen secretion, since pregnancy was not maintained by prolactin and estrone.