Regulation of Mammary Gland Metabolism

Abstract

1.A method for the preparation of isolated mammary gland cells of the rat is described. 2. The procedure involves disaggregation of the tissue in a collagenase-hyaluronidase mixture and subsequent purification of the heterogeneous population of cells by centrifugation in discontinuous Ficoll-400 gradients ; the preparation takes 60 minutes. The yield of cells is approximately 147.6.3. The cells as prepared have high rates of metabolism and synthetic capacity and exhibit metabolic characteristics comparable to intact tissue.4. Measurements of the content of metabolic intermediates show cells to have, and retain, 'outstandingly high levels of ATP and to have an energy charge close to 0.9. Levels of other intermediates approximate to those found in the intact tissue. The level of glycolytic inkrmediates below the triose phosphate stage indicate the highly aerobic state of the cells.5. The pattern and scale of glucose utilization, measured using specifically labelled glucose incorporation into I4CO2 and 14C-labelled lipid production, approximates closely in isolated cells at 5 and 20 mM glucose and in tissue slices at 20 mM glucose concentration. Mammary gland slices incubated with 5 mM glucose have a considerably lower rate of metabolism. Isolated cells exhibit a higher proportionate rate of glucose utilization by way of the pentose phosphate pathway.6. The isolated cells are hormone responsive. Insulin increases the oxidation of glucose by the pentose phosphate pathway and stimulates lipid synthesis. Addition of progesterone and cortisone in vitro (10 pM) leads to a marked and rapid decrease in the rate of glucose oxidation and conversion to lipid.The metabolic activity of rat mammary tissue varies sharply over the lactation cycle. Two transitions, that from the relatively quiescent pregnant gland to the actively secreting gland which occurs at parturition and the second from the fully active lactating gland at the end of lactation to the inactive state which results from the cessation of suckling, are controlled by shifts in the hormonal balance of the animal (see Folley [l]) and by changes in the intracellular concentrations of a few metabolites [2]. Similar factors control the progressive rise in the rate of milk formation which occurs over the whole of the lactation period in response to the increasing needs of the growing pups.

Reviews of the progress of Dairy Science: Secretion of citrate into milk

“…Plasma concentrations of citrate are generally lower than those found in mammary tissue, which are themselves lower than those in milk (see Table 1 for concentrations in milk). Concentrations of 014,0-19,0-09 /tmol/ml and 31,21 and 038 /tmol/g tissue have been reported for the citrate concentration in blood and mammary tissue of the cow, goat and rat respectively (5,7,10,19,24,77). Values for tissue citrate are probably an overestimate because of contamination with milk, and do not of course necessarily indicate the concentration in intracellular fluid (cytosol) because of th© sequestration of citrate in organelles.…”

Role of Progesterone and Glucocorticoids in the Transcription of the beta-Casein and 28-S Ribosomal Genes in the Rabbit Mammary Gland

“…The reduction of the casein inRNA concentration by progesterone is probably insufficient to support a significant inhibition of casein synthesis. The aspecific inhibitory effect of progesterone may be ascribed to some toxic action of the steroid [25,261. Such a toxic action may also explain the inhibition of lactose synthetase activity in organ culture at least with the highest concentrations of progesterone [24.27].…”