Increased locomotor and thermogenic activity in mice with targeted ablation of the GHRH gene

Growth hormone (GH) deficiency (GHD) leads to growth failure and changes in body composition, including increased fat accumulation and reduced lean body mass in both humans and rodents. The aim of this study was to examine the factors that contribute to energy imbalance in the GH releasing hormone knock out (GHRHKO) mice, a well established model of GHD.

We evaluated food intake (of standard laboratory chow), total body weight (TBW), locomotor activity, body temperature and interscapular brown adipose tissue (BAT) weight in 8 adult male mice homozygous for the GHRHKO allele (-/-) and 8 heterozygous (+/-) animals as controls. The gene expression of uncoupling protein-1 (UCP-1) in BAT and the levels of norepinephrine (NE), dopamine (DA), and serotonin (5-hydroxytryptamine, 5-HT) in the ventral striatum were measured by real-time reverse transcription polymerase chain reaction (RT-PCR) and high performance liquid chromatography (HPLC) analysis, respectively.

Throughout 2 months of observation -/- mice consumed approximately 40% more food (normalized to TBW; P<0.001), and showed increased locomotor activity in 24h time compared to controls (P<0.05). Moreover, -/- animals showed increased body temperature (P<0.001), BAT weight (P<0.001), and UCP-1 gene expression (P<0.001), while NE levels in the striatum area were lower (P<0.05) than controls.

The present study demonstrates that the increased food intake observed in GHRH ablated animals is associated with increased locomotor and thermogenic activity.