Anterior Pituitary: Physiology of Pituitary Hormones | Harrison's Endocrinology, 4e | AccessBiomedical Science

INTRODUCTION

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.

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, TEF

SF-1, DAX-1

Fetal appearance

6 weeks

8 weeks

12 weeks

Hormone

POMC

PRL

TSH

FSH, LH

Protein

Polypeptide

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/L^a

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.

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.