Lactation litter size differentially affects satiety hormone concentrations and gut adaptations in Wistar rat dams

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Introduction: Peptide-YY (PYY) is a satiety hormone secreted by the colon. We have previously shown that PYY significantly increases in early lactation in rats, despite hyperphagia. Increased PYY may be associated with significantly increased gut growth by late lactation in dams with average-sized litters. Our aim was to determine whether feeding different litter sizes influences postpartum changes occurring during the maternal adaptation to lactation. Materials and Methods: Wistar rats had litter sizes adjusted to 4, 8 (standard) or 12 pups by 1 day postpartum and were sacrificed at day 25 of lactation. Colonic PYY was quantified using radioimmunoassay. Gut tissue measurements were standardised by free-floating gut for length measurements and using nicardipine for circumference measurements. Results and Discussion: Dams feeding 4 pups had significantly shorter and lighter small and large intestines and lighter caecums compared with dams feeding 8 pups and we hypothesise that this is due to reduced suckling demand. Significantly increased descending colon PYY in dams with 8 pups was associated with increased gut size in these dams. Despite no increase in gut length or wet weight, dams feeding 12 pups had significantly increased gut circumferences, which may represent an adaptation to lactation that requires less energy. Energy insufficiency for structural modifications may be why dams feeding 12 pups showed different adaptations to dams feeding 8 pups. This study is the first time such differential adaptations have been shown in dams due to litter size; further work is being carried out to establish if pups from different sized litters have altered endocrine profiles or gut structure that influence feeding.