Oxytocin is produced by the posterior pituitary that helps in the process of parturition. Melatonin is secreted by the pineal gland and regulates the normal rhythm of sleep-wake cycle. Progesterone is the hormone secreted by the corpus-luteum that aids in maintenance of pregnancy. Atrial natriuretic factor is a polypeptide hormone secreted by the heart atria in response to atrial stretch and decreases the blood pressure.