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.
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.
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