Abstract
Ghrelin, a peptide hormone secreted by the stomach, stimulates both appetite and reward signalling. Its deletion in mice results in poor recovery from metabolic challenges, like starvation, but does not affect food intake or body weight. While sex differences in appetite and feeding behavior have been reported, little is known about the role of ghrelin herein. To investigate this, we used a metabolic cage system to continuously monitor responses of ghrelin-deficient (GKO) and wildtype (WT) mice to three different diets. Male and female mice (5 weeks old) were housed individually in a Promethion system (Sable Systems, USA) and provided one of three diets for 9 weeks: RA, continuous chow with restricted access to a Western-style diet (WD; 2h access, 3d/week) in the light phase; CA, continuous access to both diets; CC, continuous chow. Glucose tolerance was assessed at week 7 by IPGTT; food intake (kcal/g bodyweight), energy expenditure and locomotor activity at week 8; body weight and body composition (EchoMRI, USA) at week 9. On access days, RA mice ate up to 60% of their 24h intake during the WD access period. Following WD access GKO RA mice ate less chow than WT RA mice. Intriguingly, this compensatory reduction in food intake by GKO mice occurred at different times for males and females. GKO RA males ate 45% less chow in the dark phase immediately after WD access (p < 0.001). In contrast, this reduction in food intake (30% less) did not occur until the following, non-access, day in GKO RA females (genotype-sex: p < 0.05). Depending on diet, GKO mice showed differential regulation of energy expenditure in the light phase. Energy expenditure was 6–17% higher in GKO than WT mice in the RA group on access days and in the CA group. On non-access days, however, GKO mice in the RA group expended 13% less energy than WT RA mice (p < 0.005). Regardless of diet, locomotor activity in females was greater than in males (p < 0.001). However, GKO females in the RA and CC groups showed a marked 30% reduction in locomotor activity compared to WTs (genotype-sex: p < 0.05). After nine weeks, neither sex nor genotype effects were seen in body weight gain and composition of RA animals. CA females gained 17% more body weight and had a 6.1% higher fat percentage than CA males (both p < 0.001). In the CC group body weight gain did not differ, but GKO females had 3.1% more fat than WT females (genotype-sex: p < 0.01). Glucose tolerance (AUC) was similar in all groups. In conclusion, we demonstrated that ghrelin deficiency changes the response to the three diets in a sex-dependent manner. Especially, restricted access to WD differentially affected food intake timing and locomotor activity of male and female GKO mice. These results add to the growing body of evidence that ghrelin signalling is sexually dimorphic.
Development of obesity in transgenic rats with low circulating growth hormone levels: involvement of leptin resistance