Role of the small intestine in postpartum weight retention in mice

Background: 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. Objective: 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 post-partum weight gain. Design: 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). Results: 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 s 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 ≤ 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. Conclusions: 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.