Assay with the Guinea Pig of the Lactogenic Hypophyseal Hormone. ∗

Abstract

Corner's 1 results on mammary stimulation in virgin ovariecto-mized rabbits by injections of hypophyseal extracts were confirmed by Nelson and Pfiffner 2 in guinea pigs. They obtained lactation in 3 ovarieetomized, virgin guinea pigs following injections of hypophyseal extracts alone.

In our own investigations of the lactogenic hypophyseal hormone,† rats, rabbits, guinea pigs, cows, dogs, a monkey and an opossum have been used. Lactation was readily induced in all forms except the rat, which was poorly responsive. We have also used the squab test of Riddle et at 3 for lactogenic hormone on some hundred birds. While satisfied with it, more particularly because the test animals may be used for simultaneous assay of other anterior pituitary hormones, we have nevertheless been interested in using the guinea pig as a favorable mammalian form in which to study mammary response. We have observed lactation in more than 100 virgin guinea pigs (600-700 gm.) ovariectomized in oestrus and injected immediately thereafter with lactogenic hormone. Such animals, contrary to Riddle's 3 opinion, are very reactive without previous injections of ovarian hormones (the influence of preceding ovarian cycles probably suffices to “prepare” the gland). Virgins in oestrus are chosen because at this time of the cycle a few drops of clear, watery fluid containing colostrum-corpuscles may be expressed from the gland, indicating that the gland is at the height of its cyclical growth. 4 To date we have never observed milk secretion in normal or ovariectomized virgin guinea pigs uninjected with the lactogenic hormone. As early as 8 hours following the injection of the lactogenic principle, the serous secretion may be replaced by a turbid one; and it has been possible following potent hormonal injections to express milk in streams within 24 hours.