Low resting metabolic rate and increased hunger due to ß-MSH and ß-endorphin deletion in a canine model.

Mutations that perturb leptin-melanocortin signaling are known to cause hyperphagia and obesity, but energy expenditure has not been well studied outside rodents. We report on a common canine mutation in pro-opiomelanocortin (POMC), which prevents production of ß-melanocyte-stimulating hormone (ß-MSH) and ß-endorphin but not α-MSH; humans, similar to dogs, produce α-MSH and ß-MSH from the POMC propeptide, but rodents produce only α-MSH. We show that energy expenditure is markedly lower in affected dogs, which also have increased motivational salience in response to a food cue, indicating increased wanting or hunger. There was no difference in satiety at a modified ad libitum meal or in their hedonic response to food, nor disruption of adrenocorticotropic hormone (ACTH) or thyroid axes. In vitro, we show that ß-MSH signals comparably to α-MSH at melanocortin receptors. These data implicate ß-MSH and ß-endorphin as important in determining hunger and moderating energy expenditure and suggest that this role is independent of the presence of α-MSH.

Obesity risk factors in British Labrador retrievers: Effect of sex, neuter status, age, chocolate coat colour and food motivation.

BACKGROUND: Canine obesity is a complex disease affected by genetic, endocrine and environmental factors. It is associated with reduced lifespan and many comorbidities. Prevalence differs by breed, with Labrador retrievers at high risk. Past data on how biological risk factors impact weight gain have been contradictory, possibly because they were obtained from genetically heterogeneous populations. METHODS: We investigated risk factors for canine obesity in a population of British Labrador retrievers (n = 521) with high-quality data on obesity, weight, owner-reported food motivation and related characteristics. We used linear regression to assess known and novel risk factors for obesity. RESULTS: We found that neutering increased obesity in males (p < 0.001) but not females (p = 0.37). Older age was associated with obesity in female Labradors (p = 0.013) but not males (p = 0.49). We identified two new risk factors for obesity in Labrador retrievers: chocolate coat colour (p < 0.001) and high food motivation (p < 0.001). LIMITATIONS: Strategic recruitment to collect both obese and lean dogs means this cohort is not suitable for assessing obesity prevalence in UK Labrador retrievers. CONCLUSION: Studying this genetically homogeneous population informs our knowledge of common risk factors for obesity and expands those relevant to Labrador retrievers.