Hypothalamic–pituitary–target-organ axis Hypothalamic–pituitary–target-organ axis. The hypothalamic hormones regulate the biosynthesis and release of eight pituitary hormones. Stimulation of each of these pituitary hormones produces and releases trophic hormones from their associated target organs to exert their principal effects. These trophic hormones regulate the activity of endocrine glands. Subsequently, increased serum concentration of the trophic hormones released from the target organs can inhibit both the hypothalamus and the anterior pituitary gland to maintain homeostasis (negative feedback). Inhibin is produced by the testes in men and the ovaries in women during pregnancy. Inhibin directly inhibits pituitary production of follicle-stimulating hormone (FSH) through a negative feedback mechanism. Melanocyte-stimulating hormone (MSH) produced by the anterior pituitary is not illustrated in the figure. (−), inhibit; (+), stimulate; ACTH, adrenocorticotropic hormone (corticotropin); ADH, antidiuretic hormone (vasopressin); CRH, corticotropin-releasing hormone; FSH, follicle-stimulating hormone; GABA, γ-aminobutyric acid; GH, growth hormone (somatotropin); GHIH, growth hormone–inhibiting hormone (somatostatin); GHRH, growth hormone–releasing hormone; GnRH, gonadotropin-releasing hormone; IGF-I, insulin-like growth factor-I; LH, luteinizing hormone; LHRH, luteinizing hormone–releasing hormone; PRH, prolactin-releasing hormone; T3, triiodothyronine; T4, thyroxine; TRH, thyrotropin-releasing hormone; TSH, thyroid-stimulating hormone (thyrotropin). Source: Endocrinologic Disorders, Pharmacotherapy Principles & Practice, 3e Citation: Chisholm-Burns MA, Wells BG, Schwinghammer TL, Malone PM, Kolesar JM, DiPiro JT. Pharmacotherapy Principles & Practice, 3e; 2013 Available at: http://ppp.mhmedical.com/DownloadImage.aspx?image=/data/books/1450/chi_ch46_f001.png&sec=81153322&BookID=1450&ChapterSecID=81142587&imagename= Accessed: October 31, 2017 Copyright © 2017 McGraw-Hill Education. All rights reserved