Changes in appetite hormones and gut tissue architecture during the rat reproductive cycle, pregnancy and lactation

Johnson, Michelle; Saffrey, Jill and Taylor, Victoria (2013). Changes in appetite hormones and gut tissue architecture during the rat reproductive cycle, pregnancy and lactation. In: Programming obesity: central and peripheral contributors, 14-16 Apr 2013, Cambridge, UK.



Pregnancy and lactation are known to result in changing maternal appetite and adiposity, which may also lead to long-term weight retention. With increasing obesity trends in many populations, gut peptides are being explored as a potential treatment to manipulate appetite. Many animal studies, however, have only considered males, to avoid complications of the female reproductive cycle. Ovarian hormones are known to have effects on appetite and locomotor activity in many species, including rats. Other studies have found increased concentrations of the satiety hormone peptide-YY (PYY) during pregnancy and lactation in rats, when food intake is known to increase substantially. Further clarification of the mechanisms by which appetite is modulated during these stages is required to further our understanding of how appetite could be optimally manipulated in females to improve future health status.

The aim of this work is to characterise changes to gut structure at defined stages of rat pregnancy and lactation, compared with the oestrous cycle, in order to elucidate changes in anorexigenic co-secreted gut hormones PYY and glucagon-like peptide-1 (GLP-1). Peptide levels are being measured in matched fed and fasted plasma and in fasted gut tissue samples. Detailed gut measurements will also be used to determine how changes to gut structure are related to enteroendocrine cell number or peptide concentrations. Female Wistar rats were kept under a reverse lighting schedule (lights off 11.00-23.00 hr) and all procedures were completed during the dark phase. To establish changes to gut peptides during each stage of the oestrous cycle, animals were staged daily by vaginal lavage. Fed blood samples were obtained by tail-bleed 24 hours prior to dissection. Rats were fasted from 08.00 hr on the day of dissection and fasted blood and gut samples were obtained following culling, alongside multiple gut measurements, standardised by free-floating gut and relaxation using nicardipine. Samples were similarly obtained from rats at days 4, 12 and 18 of pregnancy, and rats at days 0, 5, 10 and 25 of lactation. The oestrus dance was utilised as a tool to reliably and predictably time-mate rats for early pregnancy time-points. Tissues were extracted with acetic acid.

Concentrations of total peptides in plasma and gut tissue extract were determined using radioimmunoassays. No change in body weights in relation to the oestrous cycle was found, with expected increased body weights during pregnancy and decreased body weights throughout lactation. Although fasted prior to dissection, small amounts of stomach contents (mean=0.6g; range: 0.04-1.8g) were often present. Weights of stomach contents were significantly lower after the transition from proestrus to oestrus (F(3,39)=3.2, P=0.034) in reproductively cycling rats. GLP-1 concentration in descending colon tissue, but not in fed or fasted plasma, was significantly higher at proestrus than during oestrus or diestrus (F(3,39)=3.9, P=0.015). PYY concentration in the same tissue demonstrated a non-significant tendency to show the same pattern of concentration as GLP-1 throughout the cycle (P=0.079).

In summary, observed increases in satiety hormone tissue concentrations, supported by reduced fasted stomach contents during proestrus, could contribute to the reported reduction in food intake at this time during the rat oestrous cycle.

In pregnant and lactating dam samples, work is currently being performed to quantify changes to circulating and gut tissue peptide concentrations, which will be further explored alongside observed physical changes to the gut. Both small (F(7,49)=20.5, P<0.001) and large (F(7,47)=11.1, P<0.001) intestine lengths were observed to increase throughout lactation. Stomach tissue weight (F(7,48)=12.6, P<0.001) and small intestine weight (F(6,37)=21.1, P<0.001) also peaked at later lactation time-points. As previously reported by others, we have shown that lactation in particular results in substantial changes to gut structure. Additionally, we are using radioimmunoassay and immunofluorescence to quantify peptide concentrations and enteroendocrine cell number respectively, to determine whether observed changes to gut size results in changes in cell number. This will allow us to establish whether changes to enteroendocrine cell number contribute to differences in circulating or tissue peptide concentrations during different female reproductive states.

Viewing alternatives

No digital document available to download for this item

Item Actions