Hormonal Control of Lactation
The problems involved in the hormonal control of lactation are extremely complex, and researches now in progress, while adding to our knowledge of the factors at work, have not led to the postulation of any all-embracing or coherent theory. Ample evidence for this statement is given in the comprehensive review by Folley,' to whose work we referred in a leading article on lactation in July of last year. At the moment the chief interest in this country is focused on the actions of oestrogens and pituitary fractions and their relations. It is by now well established that mammary development may be incited in most mammals by combined treatment with an oestrogen and progesterone. In general, oestrogens appear to stimulate duct development and progesterone appears to be responsible for alveolar growth. There is no clear-cut evidence that these actions are direct, for experiments in hypophysectomized animals. have given conflicting results in the hands of different workers. In this connexion Speert2 performed an interesting experiment by painting the left nipples of immature male monkeys with an alcoholic solution of oestrone, the right nipples being painted with alcohol alone. He found that the oestronetreated mammae enlarged while the control right nipples were uiaffected, which goes to show that the pituitary was not involved. This conclusion, however, at present applies only to the mammary glands of the immature male monkey, because one of the most confusing factors in research on lactation has been the quite different results obtained by similar procedures in different species and in the different sexes of the same species. The technique of unilateral inunction does, however, provide a method for testing the direct action of hormones absorbed through the skin without removing the animal's own glands, which inevitably results in undesirable and usually uncontrollable secondary effects. Turning to the question of the secretion of milk by the mammary glands when they are fully developed, the pituitary is found to be accepted as the most important factor at work. It is perhaps unfortunate that the early researches of Riddle showed that anterior pituitary extracts which initiate lactation in a variety of species would also cause the growth of crop-glands in the pigeon. This was made the basis of an assay method for preparations and was almost universally adopted. It is only lately that it has been appreciated that this method of assay has distinct disadvantages. It is now realized that an extract capable of stimulating the pigeon's crop-gland does not necessarily initiate milk secretion in mammals. The commercial preparations of prolactin at present available are usually standardized by the crop-gland response, a fact which may accouint for conflicting clinical reports. Folley' therefore proposes that the name " prolactin " should be confined to crop-stimulating activity, and Folley and Young3 suggest the term " galactopoietic factor " for the anterior pituitary fraction responsible for increasing the milk yield of an animal already producing milk. " Lactogenic " is applied to the initiation of lactation in hypophysectomized animals. Folley and Young in their experiments showed that injections of crude anterior pituitary extracts increase the milk yield in cows in declining lactation to a greater extent than do purer preparations containing seven times as much prolactin (crop-stimulating) activity. This leaves open the question whether prolactin is galactopoietic, but proves that there is a distinct galactopoietic factor in the pituitary apart from a prolactin, or a principle which, acting with prolactin, has a synergistic galactopoietic effect. The present difficulty
Further Observations on the Effect of Hypophysectomy on Lactation
The removal of the pituitary from a lactating rat leads promptly to a cessation of milk secretion. 1 Immature female rats treated with the anterior-pituitary-like hormone long enough to induce full development of their mammary glands secrete milk when the luteinized ovaries are removed, but not if the pituitary is removed at the same time. 2 These observations seem to support the view of Riddle 3 and others who believe that lactation is controlled by a pituitary hormone, prolactin. Less easily reconciled with this view was the observation 4 that pregnant rats hypophysectomized 10 days before term showed milk secretion for a few hours after parturition. It seemed possible that in these last experiments pituitary function was partly replaced by some stimulus from the pregnant uterus. We found in 10 experiments that if the uterus was emptied by Caesarian section late in pregnancy, lactation set in within 36 hours; similar observations have been made in the guinea pig 5 and the goat. 6 In 6 other experiments, however, in which the pituitary was removed when the uterus was emptied, no milk secretion was observed. This indicates that milk secretion is not possible in the rat if both the fetuses and the pituitary are absent.
HAS OVOTHERAPY, AS NOW PRACTICED, AN EXPERIMENTAL BASIS ?
INTRODUCTION Our knowledge relating to the function of the corpus luteum is limited to a few isolated and disjointed facts. The minority are based on reliable experimental data ; the majority are insecurely founded on clinical observations, which permit of widely differing interpretation. Even a cursory study of the corpus luteum under the microscope will convince an unbiased observer that a structure which is stamped with all the hallmarks of an extremely active gland must possess at least some, and probably important functions. As Fraenkel has shown, the corpus luteum is widely distributed in the mammalian series. It should be classed among the glands of internal secretion, enjoying the unique distinction of being transitory, appearing with each cycle of rut or menstruation, and persisting during the major part of gestation. The voluminous literature dealing with the corpus luteum is readily accessible.1In this connection only the following articles need