What is known about secretin?
- 27-aa peptide
- inhibits gastric acid secretion
- stimulates pancreatic bicarbonate production
New circuit
Intestinal secretin courses through the blood and acts on secretin receptor expressed in brown adipose tissue to generate heat.
Independently, the hypothalamus also senses secretin to generate a satiety response.
Meal-induced thermogenesis
Meal-induced thermogenesis is the increase in energy expenditure caused by the obligatory cost of digesting, absorbing, and storing the ingested food and a facultative component in response to sympathetic nervous system stimulation.
The interesting spin, is that the whole body generates energy, such that 10% of daily energy expenditure is through meal-induced thermogenesis.
Secretin increases oxygen consumption in primary brown adipocyte culture. This is interesting because it is via a mechanism independent of sympathetic neuron stimulation.
In vivo secretin injections
Observations
Mice generate heat when injected with secretin, in a Ucp1-dependent manner (indicative of active brown adipose tissue). Mice show pronounced reduction in food intake.
Humans show increased glucose uptake (using a fluoro-glucose analog PET ligand) in their brown adipose tissue when injected with secretin.
Human relevance
Secretin appears to have mainly be a short-term effect on food intake. Chronic secretion exposure had minimal effects on weight and fat loss. Knockouts of secretin or its receptor have no effect. Like Cck, animals can compensate for the secretin modulations.
Humans have less brown fat than mice. So it is not clear if this will sufficiently engage the hypothalamus for the satiety circuit.