Reproduction Abstracts

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 <1 day postpartum pups remained with the dams throughout. Appetite hormone levels were quantified using radioimmunoassay. Statistical analyses were performed on measured appetite hormone concentrations, and on concentrations that were corrected for body mass.

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.