Lactation Litter Size Research Articles

Pup sex and body mass of rats raised in different lactation litter sizes affect ghrelin and peptide-YY concentrations

Introduction: Previous studies have established that litter size during lactation influences body size and adiposity in male rat pups, but female pups and appetite-regulatory hormones have not been studied in this way. Gastrointestinal hormones ghrelin and peptide-YY (PYY) have roles in appetite regulation: high ghrelin levels signal hunger high PYY levels signal satiety. Both hormones are also associated with altered body mass and body composition. Previous findings (SRF 2014) demonstrated that lactation litter size affected levels of appetite hormones in gastrointestinal tissue, but not in plasma. Observed changes in hormone concentrations may have been further influenced by significant differences in pup body size between small and large litters, thus additional data analysis accounting for body masses presented here aims to establish the effects on male and female pups being suckled and raised in different sized litters. Methods: Male and female littermates from small (n=4), control (n=8) and large (n=12) litter sizes were studied at weaning, with litter sizes adjusted Results and discussion: Pups raised in smaller litters were significantly larger (P<0.001). No differences were found in measured concentrations of either ghrelin or PYY in plasma between the litter sizes. Correcting for body mass revealed that large pups raised in small litters had the least circulating ghrelin (P=0.002) and PYY (P<0.001). Analysing by pup sex further revealed that although plasma ghrelin concentrations were only significantly lower in these larger males (P=0.023), PYY levels were significantly lower in both the males (P=0.011) and females (P=0.032). This work highlights the importance of taking into consideration factors such as body mass and sex when investigating hormones that affect body composition.

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

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.

Sex differences in gut satiety hormones peptide-YY and glucagon-like peptide-1 in pups raised in larger lactation litter sizes

Introduction: Previous studies have established that the size of litters during lactation influences body size and adiposity in male rat pups. Levels of gut hormones such as appetite-stimulating ghrelin and appetite-reducing peptide-YY (PYY) and glucagon-like peptide-1 (GLP-1) have not been examined in this model despite an increased susceptibility to obesity into adulthood. This study aimed to establish whether changes in gut appetite hormones, resulting from lactation litter size, could contribute to the increased risk of adulthood obesity. Methods: Male and female littermates from small (n=4), control (n=8) and large (n=12) litter sizes were studied at weaning age (25 days), with litter sizes adjusted prior to 1 day postpartum; pups remained with the dams throughout the study. Stomach ghrelin and colonic PYY and GLP-1 were quantified using radioimmunoassay. Stomachs were emptied, blotted dry and weighed. Body length was taken from between the front paws to the anus. Results and Discussion: No differences were found in stomach ghrelin levels between the pups, but levels of the gut satiety hormones PYY and GLP-1 were found to be altered in colon tissue. In descending colon, PYY and GLP-1 concentrations were significantly lower in male, but not female, pups from the large litters. Physically, both the male and female pups fed in the large litters were significantly shorter and lighter and had significantly lighter stomach tissue. We suggest that the significantly smaller male pups may have had reduced satiety as a mechanism to achieve ‘catch-up growth’ into adulthood. It is unclear whether females may show similar adaptations at a later stage. This study further demonstrated differences between young males and females, with differences evident even before sexual maturation. This work highlights the importance of standardising litter size as early as possible, especially in studies of appetite control.

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

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.

Radioimmunoassay of endogenous and exogenous prolactin in milk of rats.

SUMMARY Immunoreactive rat prolactin was detected in rat milk. Increasing volumes of milk decreased the percentage of 131I-labelled rat prolactin bound to antiserum in a manner parallel to the decreases produced by increasing log doses of standard hormone and blood serum. Rats suckling litters of 4, 8 or 12 pups were milked at various stages of lactation and prolactin concentrations (ng/ml) in milk varied significantly both with stage of lactation and with litter size. Mean prolactin levels were maximal on day 4 to day 15 and they decreased sharply near the end of lactation. At every stage of lactation litter size tended to influence prolactin concentrations with larger litters always being associated with more prolactin per millilitre of milk. Intraperitoneal injection of 1 mg bovine prolactin into lactating rats promptly caused the appearance of high levels of this foreign hormone in rat milk without significantly affecting the concentration of the native hormone.