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
An Experimental Enquiry into the Factors which Determine the Growth and Activity of the Mammary Glands
The correlation between the mammary glands and the other organs concerned in generation presents perhaps the most striking example of the interdependence of the growth and activities of different organs of the body. Although the manner in which this correlation is brought about has been the subject of speculation for many years, especially among medical men, it is only quite recently that any attempt has been made to apply experimental methods to its explanation. In the case of the mammary glands we have organs which are present in both sexes, and at birth are in the same immature condition. In both sexes there is frequently, during the few days after birth, an enlargement of the glands and an actual secretion of fluid, which is known as “witch’s milk.” This state of activity disappears at the end of the first or second week, and till puberty the glands remain in the same undeveloped condition. At this period in Man the first difference appears between the mammary glands of the two sexes, a rapid growth taking place in the female, and accompanying the commencement of the ovarian functions.
On the ovarian factor concerned in the recurrence of the oestrous cycle
IT is now generally recognised that the menstrual cycle in man and the oestrous cycle in animals cease to occur after double ovariotomy, and that in those cases in which heat and menstruation have been supposed to take place after spaying or surgical removal of the ovaries, the occurrence of the phenomena has been due to the fact that the operation was incomplete. Thus it has recently been shown that in "so-called" spayed sows which experienced heat and behaved more or less like normal unoperated animals ovarian tissue had been left at the time of the operation and had subsequently hypertrophied(ui). Moreover, it has been shown by several investigators that successful transplantation of the ovaries to abnormal positions such as the ventral peritoneum or the tissues of the kidney does not inhibit the recurrence of the cycle, for the uterus in such animals retains its normal functional activity instead of undergoing atrophic changes(s, 9, 14). The inference drawn from these experiments is that heat and menstruation are brought about by some chemical substances or hormones which are elaborated by the ovaries and act either directly or indirectly upon the tissues of the uterus and mammary glands, as well as upon all the other organs which undergo cyclical changes associated with the female sexual functions. The object of the present investigation was to elucidate the problem as to what part of the ovary is responsible or mainly responsible for the recurrence of the prooestrum and oestrus. The problem had already been approached by physiologists, and notably by Pfliiger(15) and Strassmannol, and more recently by Fraenkel(4). The views of Pfluger and the older investigators may be dismissed briefly, since they assumed that the finctional correlation between the ovaries and uterus was nervous in character, and this is now known to