Sodium Metabolism and Requirements in Lactating Rats

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Abstract
Sodium metabolism was studied in 4 groups of 11 lactating rats fed a diet containing either 0.03, 0.05, 0.07 or 0.09% sodium. Less feed intake, a loss in body weight and smaller pups at weaning were found with the group fed the 0.03% sodium compared with the 3 higher sodium groups. Plasma and bone sodium were lowest in the 0.03% sodium group following lactation, whereas no differences were found among the 3 higher sodium groups. There were no differences in blood cell volume or bone moisture among the groups. Milk samples taken on day 22 of lactation showed a higher fat content for the 0.03% sodium group, whereas the sodium concentration was significantly lower for the 0.03% than for the 0.09% group. Adrenal zona glomerulosa areas were largest for the 0.03% group, next largest for the 0.05% group and smallest for the 0.07 and 0.09% groups. Kidney juxtaglomerular granulation was greatest in the rats fed 0.03% sodium. With this nonpurified diet, 0.05% sodium was adequate for rats nursing 9 pups.