ASSESSMENT OF MAMMARY-GLAND METABOLISM IN THE SOW .2. CELLULAR METABOLITES IN THE MAMMARY SECRETION AND PLASMA DURING LACTOGENESIS-II

The concentrations of lactose, glucose, glucose 6-phosphate, glucose 1 -phosphate, UDPglucose, UDPgalactose, UDP, UMP, inorganic phosphate, A DP and AMP (metabolites involved in the lactose synthesis pathway), an d cAMP, galactose and fructose were measured in the mammary secretion from sucked (n = 9) and unsucked (n = 4) mammary glands of nine sows d uring the first 5 d post partum. The concentrations of lactose, glucos e, galactose and fructose were also measured in plasma during this tim e. The progressive increase in the concentration of lactose, and chang es in the concentrations of cellular metabolites in the mammary secret ion from sucked glands were consistent with an increase in the metabol ic activity of those glands during lactogenesis II. In contrast, unsuc ked glands showed a progressive decrease in the concentration of lacto se, while the concentrations of cellular metabolites in the milk gener ally remained unchanged. These results indicated that there was no inc rease in the metabolic activity of unsucked glands (no increase in lac tose synthesis or utilization of glucose and ATP) and that the rate of lactose synthesis prior to milk removal was limited by the availabili ty of glucose and/or UDPgalactose. Therefore, the removal of colostrum from the mammary gland was necessary for an increase in the rate of l actose synthesis (and probably de novo fatty acid synthesis) and impli es that autocrine mechanisms are operating to control the rate of milk synthesis during lactogenesis in the sow. The low concentration of gl ucose in colostrum compared with that in plasma is discussed in view o f the paracellular pathway.