Long-term dietary restriction influences plasma ghrelin and GOAT mRNA level in rats

Abstract

The objective of this study was to examine the effect of chronic dietary restriction on the physical characteristics of the intestine and gut-derived satiety hormone production. Male Wistar rats (8 weeks) were randomized to ad libitum (AL) or 35% dietary restriction (DR) for 5 months. At the end of the study, physical measurements were made on the intestine and satiety hormone secretion and mRNA expression determined. A comparison group of young, growing AL rats (5 weeks) was also examined. The adult DR rats gained less weight over 5 months and had lower fat mass than adult AL rats (p<0.05). The weight of the small intestine as a percentage of total body weight was greater in adult DR compared to adult AL but lower than young AL rats. Compared to AL, DR down-regulated proglucagon and cholecystokinin mRNA in the duodenum and ghrelin mRNA in the stomach of adult rats but was not different from young AL. Ghrelin-O-acyltransferase (GOAT) mRNA in the stomach was up-regulated 21-fold in adult AL rats compared to young AL and 14-fold compared to adult DR rats. Total and des-acyl ghrelin was approximately 50% higher in adult DR and young AL rats compared to adult AL. Plasma leptin and insulin were lower in adult DR and young AL rats compared to adult AL. Our findings suggest that long-term energy deficits continue to drive up ghrelin levels which may have profound implications for practical implementation of DR as an anti-aging or anti-obesity strategy in humans.

Fig. 1

Intestinal proglucagon mRNA expression in young and adult ad libitum versus dietary-restricted rats. Results represent the mean±SEM for 8 adult AL (ad libitum), 9 adult DR (dietary restriction), and 6 young AL rats. Gene expression is expressed as a fold change from the young AL rats for which the value is set at 1.0. Using the 2^−ΔΔCT calculation each gene is corrected against the housekeeping gene actin. Values with different letters represent a difference between groups within a given intestinal segment (p<0.05). Where no letters are present there are no differences between groups.

Fig. 2

Gene expression of (A) ghrelin, cholecystokinin (CCK), peptide YY (PYY), and (B) GOAT mRNA in young and adult ad libitum versus dietary-restricted rats. Results represent the mean±SEM for 8 adult AL (ad libitum), 9 adult DR (dietary restriction), and 6 young AL rats. Gene expression is expressed as a fold change from the young AL rats for which the value is set at 1.0. Using the 2^−ΔΔCT calculation each gene is corrected against the housekeeping gene actin. Values with different letters are significantly different within a given gene (p<0.05).

Fig. 3

Plasma leptin, insulin, total ghrelin and des-acyl ghrelin concentrations in young and adult ad libitum versus dietary-restricted rats. Results represent the mean±SEM for 8 adult AL (ad libitum), 9 adult DR (dietary restriction), and 6 young AL rats. Blood was sampled in the morning ~2 h into the light cycle. Des-acyl ghrelin concentrations were not measured in the young AL rats due to a limited volume of plasma. The bar in the graph represents an estimated level from the known proportion of total ghrelin concentrations measured in the adult DR and AL rats. Values with different letters are significantly different within a given hormone (p<0.01).

Fig. 4

Plasma amylin, GLP-1 and glucagon concentrations in young and adult ad libitum versus adult dietary-restricted rats. Results represent the mean±SEM for 8 adult AL (ad libitum), 9 adult DR (dietary restriction), and 6 young AL rats. Blood was sampled in the morning ~2 h into the light cycle. Values with different letters are significantly different within a given hormone (p<0.01).