Autocrine Control of Milk Secretion: Development of the Concept

Abstract

Over the past twenty years it has been established that the mammary gland is subject to more than one level of physiological control. The ultimate pattern of parental expenditure is obviously subject to natural selection and is, therefore, controlled genetically. The strategic level decisions, which may also involve interplay between mother and young, are signalled to the mammary gland by the endocrine system (see Peaker, 1989). This strategic level of control is then subject to environmental constraints, including nutrition, which can modify the rate of milk secretion systemically (see Loudon and Racey, 1987; Peaker, 1989). Such plasticity in the rate of milk secretion also appears to be mediated mainly, if not solely, by the endocrine system. However, these strategic and environmental forms of control, exerted systemically, are modulated by a tactical control mechanism operating within each mammary gland to set the actual rate of milk secretion. This local, intra-mammary mechanism responds to the frequency or completeness of milk removal by the young or by milking in dairy animals. The intra-mammary control of secretion has now been shown to operate in all mammals which have been studied&3x2014;from dairy cows and goats to marsupials and man. This article describes the discovery of local control and its mechanism.