The pituitary gland, a grape-size gland located at the base of the brain, consists of two primary lobes: the anterior pituitary produces and secretes six hormones, while the posterior pituitary secretes two hormones. These anterior pituitary hormones stimulate endocrine glands, regulating their hormonal secretions. In the 1930s, the English anatomist Goeffrey Harris hypothesized that the hypothalamus, which lies directly above the pituitary, controls it by secreting its own hormones, but he was unable to identify such hypothalamic hormones and to prove his hypothesis. Although only the size of an almond, the pituitary controls a wide range of basic bodily functions, as well as emotions. During the late 1950s and into the 1960s, Roger Guillemin and Andrew V. Schally—first as collaborators at Baylor University in Houston, Texas, and later as rivals—successfully identified a number of hypothalamic hormones. These hormones are secreted at the base of the hypothalamus and travel through a number of blood vessels to the anterior pituitary, where they either stimulate or inhibit the release of specific hormones.
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| This illustration depicts the hypothalamic-pituitary axis. Hormones from the hypothalamus stimulate or inhibit the release of hormones from the anterior pituitary gland. These pituitary hormones, in turn, travel in the blood to different endocrine glands, activating the release of specific hormones. |
In 1968, the first such hypothalamic hormone was isolated and chemically characterized: Thyrotropin-releasing hormone (TRH), which stimulates the release of thyroid-stimulating hormone (TSH) from the anterior pituitary. TSH travels in the blood to the thyroid gland, promoting the secretion of the thyroid hormones. The hypothalamus and anterior pituitary do not function in isolation; rather, they receive messages or negative feedback from nerves throughout the body, which modulate or turn off additional TRH and TSH secretion. Other hypothalamic hormones include luteinizing hormone-releasing factor, adrenocorticotropin-releasing hormone, and somatotropin. Guillemin and Schally, the founders of neuroendocrinology—the interaction between the central nervous system and endocrine glands—were co-recipients of the 1977 Nobel Prize, which they shared with Rosalyn Yalow for her discovery of the radioimmunoassay (RIA) of these hormones.