Dehydrogenases and nucleic acids in rat mammary gland during involution initiated at various stages of lactation

Do inflammatory cells participate in mammary gland involution?

The processes by which the involuting mammary gland clears residual milk and milk fat, as well as apoptotic cells, have gone largely unstudied in the modern literature. Here we review the evidence for and against the involvement of professional phagocytes of hematopoietic lineage in this process. Additionally we present evidence that mammary epithelial cells themselves are capable of phagocytosis and may be responsible for the majority of apoptotic cell and residual milk clearance during murine involution. In this scheme these cells regulate their cytokine production in response to apoptotic cells in a manner similar to other cells, including macrophages. The ensuing model describes a process of involution that actively suppresses an inflammatory response in the gland, allowing for effective tissue remodeling and damage prevention.

Properties of pyruvate dehydrogenase of rat mammary tissue and its changes during pregnancy, lactation and weaning

Pyruvate dehydrogenase of rat mammary tissue showed many of the regulatory properties of the analogous enzyme in other mammalian tissues. It was inactivated in the presence of low concentrations of ATP and this rate of inactivation was slowed if pyruvate or PP(1) was also present. Reactivation by Mg(2+) in the presence of low concentrations of Ca(2+) occurred over a similar time-course. The K(m) value for Mg(2+) in this process was about 2mm. The enzyme was assayed in extracts of freeze-clamped mammary glands removed from pregnant, lactating or recently weaned rats under halothane anaesthesia. Both the initial activity and the activity after full activation (;total enzyme activity') were determined. The former parameter, when expressed on a DNA basis, varied within a range of 40 times its lowest value. Maximum total enzyme activity was about 1 unit/g wet wt. The total enzyme activity and the fraction in the active form increased in step from pregnancy to mid-lactation, remained elevated until the end of lactation and then fell steeply within 3 days after weaning. The correlation of these two parameters of enzyme activity may indicate a common regulatory factor or else an interdependence arising from inherent properties of the multi-enzyme complex.