[Hormonal regulation of lactation (author's transl)]

Abstract

Lactation is controlled by hormones from several endocrine glands. An undisturbed function of the anterior pituitary, of the adrenals, and of the ovaries is a prerequisite for a normal morphogenesis of the mammary gland. The epithelial ducts proliferative under the combined influence of estrogens, glucocorticoids and growth hormone, whereas the lobuloalveolar development depends on progesterone and prolactin in addition to the fore-mentioned hormones. During pregnancy pituitary prolactin may be substituted by placental lactogen. Milk synthesis begins in the second half of pregnancy. It is supported by prolactin and cortisol, which directly act on enzyme activities and processes of differentiation of the alveolar cells. The sudden surge in the secretion of milk after parturition is most likely due to the rapid decline of the serum levels of progesterone. The ejection of milk from the lactating mammary gland is controlled by a neuroendocrine reflex mechanism. Suckling is the appropriate stimulus for the release of oxytocin from the posterior pituitary. Oxytocin increases intramammary pressure by inducing contraction of the myoepithelial cells and thus aids in expelling the milk from the mammary glands. Maintenance of normal postpartum lactation depends on frequent and intensive suckling. Suckling does not only stimulate the release of oxytocin, but also provokes secretion of prolactin and ACTH. This increase in prolactin caused by suckling guarantees galactopoesis. Influencing secretion of prolactin has been proven to be a useful tool for regulating lactation. The experimental ergot derivative 2-Brom-alpha-ergocryptine is a potent suppressor of prolactin secretion from the anterior pituitary. In contrast to estrogens, alone or in combination with progestagens or androgens, this drug is not only effective in suppressing the onset of lactation, but also in inhibiting lactation once milk secretion had started. As to stimulating lactation in the human there is no effective drug available up to now.