Do circulating and tissue concentrations of ghrelin and peptide-YY (PYY) change during the oestrous cycle in Wistar Rats?

Johnson, Michelle; Saffrey, Jill and Taylor, Victoria (2012). Do circulating and tissue concentrations of ghrelin and peptide-YY (PYY) change during the oestrous cycle in Wistar Rats? In: Society for Reproduction and Fertility Annual Conference 2012, 9-11 Jul 2012, Edinburgh.


Introduction: Food intake is influenced by many circulating hormones and hypothalamic neuropeptides to maintain energy homeostasis. In rodents, food intake is known to decrease at oestrus, whilst food intake during pregnancy and lactation is known to greatly increase. Previous studies of gut hormone levels during reproductive states show conflicting results, probably resulting from variations in sample preparation and the form of the peptide being measured. The aim of this work is to fully elucidate changes in appetite-regulating peptides during the oestrous cycle by analysis of both circulating and tissue peptide concentrations.

Methods: Tissue and fed and fasted blood samples were taken from female Wistar rats (32-44 weeks; 230-290 g) at different time-points during the oestrous cycle, determined by daily cytological examination (HO and ethically approved).

Results and Discussion: No change in body weight in relation to the cycle was found. Although animals were fasted prior to culling, stomach contents were often present. Weight of stomach plus contents showed a tendency (P=0.079) to relate to the cycle, with least eaten between proestrus and oestrus. Uterus weight was significantly higher at proestrus (F(3,39)=8.035, P<0.001) than at other stages. To relate circulating peptide concentrations with possible changes in gut tissues during the cycle, detailed measurements were made. Body weight, but not body length, correlated with small (r=0.532, P<0.001) and large intestine (r=0.391, P=0.010) wet tissue weight and with duodenum (r=0.328, P=0.032), ascending (r=0.524, P<0.001) and descending colon (r=0.351, P=0.021) circumference. Immunoassays are being used to measure peptide concentrations in plasma and tissue in relation to cycle stage, including appetite-stimulating ghrelin and appetite-inhibiting PYY. Behavioural observations were also noted during the cycle, including the presence of an oestrus dance, seen in the majority of animals. The oestrus dance provides a useful additional tool to accurately time-mate females, helping identify early pregnancy time-points.
(Funded by the Biomedical Research Network, The Open University).

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