Two Pools of Luteinizing Hormone in the Human Pituitary: Evidence from Constant Administration of Luteinizing Hormone-Releasing Hormone

The pituitary gonadotrophin response to constant intravenous infusions of hypothalamic luteinizing hormone-releasing hormone (LH-RH), 0.2 μg/min for 4 hr, was studied in 5 normal human men. Serum LH-RH levels were measured by radioimmunoassay to confirm the constancy of the infusions. Serum luteinizing hormone levels in response to the constant LH-RH administration revealed a biphasic pattern of elevation characterized by early and late peaks. This pattern of release is similar to that of other hormones stored in granules and suggests the existence of two pools of luteinizing hormone in the human pituitary, one requiring longer LH-RH stimulation for release than the other. In contrast, serum follicle-stimulating hormone values revealed a gradual rise during the entire infusion.