What does leptin release?

Leptin doesn't actually 'release' anything per se. It's actually a protein we produce that sends signals to your brain that you're full or have had enough food for the time being. You'd think that producing more leptin would be a good thing (for weight loss), but science shows chronically overweight people actually build up resistance, so their body doesn't get the 'signal' to stop eating and they enter a spiral of weight gain. Anyhow, hope that helps...if you're interested, there are studies as of May of this year that are showing there's a protein (PTPe) that helps increase sensitivity to leptin and can combat resistance. Anyhow, hope that helped!