Melatonin is secreted by the pineal gland in the brain. The secretion of the hormone occurs in response to the light and dark cycles. Normally, its production is reduced by being in bright light.On the other hand, being in darkness stimulates melatonin release.This is why it is often called ‘the hormone of darkness’.elatonin is secreted by the pineal gland in the brain. The secretion of the hormone occurs in response to the light and dark cycles. Normally, its production is reduced by being in bright light.