RAT PLACENTAL HORMONAL ACTIVITIES CORRESPONDING TO THOSE OF PITUITARY MAMMOTROPIN

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Abstract
Rat placenta, at an early stage of development contains a substance, (or substances) with luteotropic, mammotropic, lactogenic, and crop sac-stimulating activities. Compared to pituitary mammotropin (prolactin) it is potent in the first three of these activities and weak in the last. Luteotropic activity was shown by inducing a prolonged luteal phase in the rat ovary and thus inhibiting the estrous cycle. It was also shown by injecting estrone plus placenta into hypophysectomized rats to demonstrate growth changes in the mammary gland. Placental lactogenic activity was shown in hypophysectomized-oophorec-tomized rats injected with estrone, progesterone and placenta to induce mammary growth and then with placenta with or without hydrocortisone. A better lactogenic combination was placenta plus hydrocortisone and pituitary somatotropin. By using the highly sensitive local test it was possible to demonstrate crop sac-stimulating activity in the equivalent of a single 12-day rat placenta. Three parts of the 12-day rat placenta were tested separately for mammotropic activities. All of these parts were active; but fragments of the decidua capsularis were especially potent. Wet weight equivalents of this tissue approximating 5 mg showed activity corresponding to that of about 2 mg of the purified pituitary mammotropin.