Effect of prolactin on phosphate transport and incorporation in mouse mammary gland explants

Abstract

Rillema, James A. Effect of prolactin on phosphate transport and incorporation in mouse mammary gland explants. Am J Physiol Endocrinol Metab 283: E132-E137, 2002. First published December 18, 2001 10.1152/ajpendo.0409.2001Inorganic phosphate is present in milk at a concentration that is severalfold higher than in maternal plasma. In cultured mammary tissues from 12-to 14-day-pregnant mice, the intracellular concentration of 32 PO4 was six times higher than in the culture medium after a 4-h treatment with 32 PO4. Of the principal lactogenic hormones [insulin (I), cortisol (H), and prolactin (PRL)], only I and PRL (in the presence of H and I) stimulated 32 PO4 uptake into cultured mammary tissues; H, by itself or in the presence of I or PRL, inhibited 32 PO4 uptake. All three lactogenic hormones together effected the greatest stimulation of 32 PO4 uptake. Similar hormone effects were observed with regard to 32 PO4 incorporation into lipids and trichloroacetic acid-insoluble molecules. In a time course study, the onset of the PRL stimulation of 32 PO4 uptake and incorporation occurred 8-12 h after PRL addition; in dose-response studies, the PRL effect was manifested with PRL concentrations of 50 ng/ml and above. From kinetic studies, the apparent maximal velocity of PO4 uptake was determined to be ϳ7.7 mM ⅐ h Ϫ1 ⅐ l cell water Ϫ1 ; the apparent Michaelis-Menten constant was ϳ3-5 mM. The PRL effect on 32 PO4 uptake was abolished when sodium was absent from the uptake medium. These studies thus demonstrate a complex interaction of three hormones (I, H, and PRL) in the regulation of 32 PO4 uptake and incorporation into macromolecules in cultured mouse mammary tissues.insulin; cortisol PHOSPHATE IS AN ESSENTIAL COMPONENT of milk for the nourishment of the neonate. In milk, it is present in several forms, including inorganic phosphate, colloidal phosphate, and casein phosphate and in phospholipids (5, 12). Because of the high concentration of phosphate in milk that meets the nutritional demands of the suckling neonate, copious amounts of phosphate are transferred from the maternal plasma into milk. One author (2) reported that all of the plasma inorganic phosphate is replaced every 10 min in lactating rats.Even when only inorganic phosphate is considered, its concentration in milk is 5-to 10-fold higher than in the maternal plasma. A highly efficient transport mechanism is therefore obviously present in the alveolar epithelial cells of the mammary gland. Shillingford et al. (13) recently characterized one phosphate transport mechanism in lactating rat mammary glands. Phosphate uptake was predominantly via a sodium-dependent transport mechanism, presumably located on the basolateral membrane of the alveolar epithelial cells; a sodium-phosphate symporter was postulated. Phosphate uptake occurred via a saturable mechanism with an apparent Michaelis-Menten constant (K m ) of 1.13 mM.The experiments reported in this study were carried out to characterize the effects of three lactogenic hormones [insulin, cortisol, and prol...

Effect of prolactin on inositol uptake in mouse mammary gland explants

“…This mechanism and the time-course of the PRL effect are similar to the PRL effect on several other lactogenic processes including lactose synthesis, lipid synthesis, iodide uptake, phosphate observations. * denotes less than PRL-treated controls with p < .05 uptake and incorporation into phospholipids and proteins, amino acid uptake, glucose uptake, nucleoside uptake, and casein synthesis [8][9][10][13][14][15][16]. The stimulatory effects of insulin, by itself, and the inhibitory effects of 10 -7 M cortisol, by itself, on lactational processes also have been observed in earlier studies [8][9][10][13][14][15][16].…”

“…Milk is composed of a variety of substances, some of which are synthesized in the mammary alveolar epithelial cells, whereas others are taken up directly from the maternal plasma. Examples of substances taken up directly from the plasma include sodium, potassium, chloride, phosphate, iodide, calcium, citrate, choline, carnitine, glucose , amino acids, pyrimidine nucleosides, and inositol [3][4][5][10][11][12][13][14][15][16]. A number of inositol transporters have been identified, including those that are sodium-inositol symporters [17].…”

“…* denotes less than PRL-treated controls with p < .05 uptake and incorporation into phospholipids and proteins, amino acid uptake, glucose uptake, nucleoside uptake, and casein synthesis [8][9][10][13][14][15][16]. The stimulatory effects of insulin, by itself, and the inhibitory effects of 10 -7 M cortisol, by itself, on lactational processes also have been observed in earlier studies [8][9][10][13][14][15][16]. In addition, the cooperative effects of all three lactogenic hormones (I, H, and PRL) have been well-documented [3,[5][6][7][8][9][10][11][13][14][15][16].…”

Prolactin, Cortisol, and Insulin Regulation of Nucleoside Uptake Into Mouse Mammary Gland Explants

“…During lactation the alveolar epithelial cells of the mammary gland transport numerous substances from the maternal plasma to milk. Examples of substances whose uptakes have been characterized include sodium, potassium, chloride, phosphate, iodide, calcium, citrate, choline, carnitine, glucose, and amino acids (5)(6)(7)(8)(9). Until recently, little was known about nucleoside uptake and its hormone regulation in mammary tissues.…”