A hormone is a molecule produced by the endocrine gland in response to stimulation and which acts on a target organ. Luteinizing hormone or LH is secreted by cells of the pituitary. In women, luteinizing hormone's primary role is to trigger ovulation which occurs after 36 hours in response to a sudden increase in the rate. After ovulation, it enters into the regulation of the secretion of other hormones: progesterone and estrogen. In men, luteinizing hormone is partly responsible for the production of testosterone.