The regulation of Na+-dependent anionic amino acid transport by the rat mammary gland

The regulation of anionic amino acid transport, using radiolabelled D-aspartate as a tracer, by rat mammary tissue explants has been examined. Na+-dependent D-aspartate uptake by mammary tissue increased between late pregnancy and early lactation and again at peak lactation but thereafter declined during late lactation. In contrast, the Na+-independent component of D-aspartate uptake by mammary explants did not change significantly with the physiological state of the donor animals. Premature weaning of rats during peak lactation markedly decreased Na+-dependent D-aspartate uptake by mammary tissue. In addition, premature weaning also reduced the effect of reversing the trans-membrane Na+-gradient on the fractional loss of D-aspartate from mammary tissue explants. Unilateral weaning of rats during peak lactation revealed that milk accumulation per se reduced the Na+-dependent moiety of D-aspartate uptake by mammary tissue suggesting that the transport of anionic amino acids is regulated to match supply with demand. Treating lactating rats with bromocryptine reduced D-aspartate uptake by mammary tissue explants suggesting that the transport of anionic amino acids by the rat mammary gland is regulated by prolactin. Copyright (C) 1999 Elsevier Science B.V.