Role of the small intestine in postpartum weight retention in mice

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Approximately 25% of women retain 5 kg of the weight gained during pregnancy, but the physiologic factors underlying excessive postpartum weight gain are not known. The objective of the study was to determine whether pregnancy-related adaptive increases in intestinal nutrient transport are retained after parturition and therefore contribute to postpartum weight gain. We measured body weight and intestinal nutrient transport in virgin (V, control), primiparous (P, one pregnancy), and multiparous (M, 3 pregnancies) mice at parturition (day 1), during lactation (days 14 and 21), at weaning (day 28), after weaning (day 40), and during aging (days 70, 120, 200, and 300). In M and P mice, body weight and the weight and length of the small intestine were greatest during lactation; they then decreased but did not return to prepregnancy values until 300 d after parturition. Intestinal villus heights were maximal at lactation and remained high < or = 200 d after parturition. Total intestinal transport capacity for D-glucose, D-fructose, and L-proline was also greatest during lactation, and the lactation-enhanced transport capacity was retained < or = 70 d after parturition. M mice retained more body weight and intestinal transport capacity postpartum than did P mice. Aging per se had little or no effect on body weight or intestinal weight, length, and nutrient transport. The dramatic, lactation-related increases in intestinal nutrient transport capacity were due mainly to increases in intestinal mass. Postpartum retention of pregnancy- and lactation-related increases in intestinal nutrient uptake capacity may play a significant role in postpartum body weight retention. These adaptive increases may be cumulative and may result in greater weight retention in mice with multiple pregnancies.