Effects of lactation on sodium intake in Fischer-344 and Long-Evans rats

Rats of most strains are attracted to salt in low concentrations, and this attraction is increased by pregnancy and lactation. Nonreproducing Fischer-344 (F344) rats are unusual in that they avoid saline at all concentrations, raising the question of whether lactation alters their sodium appetite. Therefore, lactating and cycling Long-Evans and F344 rats were compared in their relative consumption of water and several concentrations of saline. We found that Long-Evans rats preferred saline, but F344 rats preferred plain water. In comparison with cycling rats, lactating Long-Evans rats markedly increased saline intake whereas F344 rats exhibited only a modest increase. Lactating rats of both strains increased total fluid intake, but this increase was primarily from water in F344 rats and from saline in Long-Evans rats. It was concluded that the aversion to saline characteristic of nonreproducing adult F344 rats continues during lactation. Their aversion to sodium in pup urine may account for the low levels of maternal anogenital licking observed in the F344 strain.