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Chapter 3: Anterior Pituitary: Physiology of Pituitary Hormones

Shlomo Melmed; J. Larry Jameson

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INTRODUCTION

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The anterior pituitary often is referred to as the “master gland” because, together with the hypothalamus, it orchestrates the complex regulatory functions of many other endocrine glands. The anterior pituitary gland produces six major hormones: (1) prolactin (PRL), (2) growth hormone (GH), (3) adrenocorticotropic hormone (ACTH), (4) luteinizing hormone (LH), (5) follicle-stimulating hormone (FSH), and (6) thyroid-stimulating hormone (TSH) (Table 3-1). Pituitary hormones are secreted in a pulsatile manner, reflecting stimulation by an array of specific hypothalamic releasing factors. Each of these pituitary hormones elicits specific responses in peripheral target tissues. The hormonal products of those peripheral glands, in turn, exert feedback control at the level of the hypothalamus and pituitary to modulate pituitary function (Fig. 3-1). Pituitary tumors cause characteristic hormone excess syndromes. Hormone deficiency may be inherited or acquired. Fortunately, there are efficacious treatments for many pituitary hormone excess and deficiency syndromes. Nonetheless, these diagnoses are often elusive; this emphasizes the importance of recognizing subtle clinical manifestations and performing the correct laboratory diagnostic tests. For discussion of disorders of the posterior pituitary, or neurohypophysis, see Chap. 6.

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TABLE 3-1Anterior Pituitary Hormone Expression and Regulation
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TABLE 3-1 Anterior Pituitary Hormone Expression and Regulation
CELL CORTICOTROPE SOMATOTROPE LACTOTROPE THYROTROPE GONADOTROPE
Tissue-specifictranscription factor T-Pit Prop-1, Pit-1 Prop-1, Pit-1 Prop-1, Pit-1, TEF SF-1, DAX-1
Fetal appearance 6 weeks 8 weeks 12 weeks 12 weeks 12 weeks
Hormone POMC GH PRL TSH FSH, LH
Protein Polypeptide Polypeptide Polypeptide Glycoprotein α, βsubunits Glycoprotein α, βsubunits
Amino acids 266 (ACTH 1–39) 191 199 211 210, 204
Stimulators CRH, AVP, gp-130 cytokines GHRH, ghrelin Estrogen, TRH, VIP TRH GnRH, activins, estrogen
Inhibitors Glucocorticoids Somatostatin, IGF-I Dopamine T3, T4, dopamine, somatostatin, glucocorticoids Sex steroids, inhibin
Target gland Adrenal Liver, bone, other tissues Breast, other tissues Thyroid Ovary, testis
Trophic effect Steroid production IGF-I production, growth induction, insulin antagonism Milk production T4 synthesis and secretion Sex steroid production, follicle growth, germ cell maturation
Normal range ACTH, 4–22 pg/L <0.5 μg/La M <15 μg/L; F <20 μg/L 0.1–5 mU/L M, 5–20 IU/L, F (basal), 5–20 IU/L

aHormone secretion integrated over 24 h.

Abbreviations: M, male; F, female. For other abbreviations, see text.

Source: Adapted from I Shimon, S Melmed, in S Melmed, P Conn (eds): Endocrinology: Basic and Clinical Principles. Totowa, NJ, Humana, 2005.

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FIGURE 3-1

Diagram of pituitary axes. Hypothalamic hormones regulate anterior pituitary trophic hormones that in turn determine target gland secretion. Peripheral hormones feed back to regulate hypothalamic and pituitary hormones. For abbreviations, see text.

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ANATOMY AND DEVELOPMENT

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ANATOMY

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The pituitary gland weighs ~600 mg and is located within the sella turcica ventral to the diaphragma sella; it consists of anatomically and functionally distinct anterior and posterior lobes. ...

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