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`MCGmw-Hiil
`A Division of The McGraw-Hill Companies
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`32
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`Goodman and Gilman’s Tllli Pl{ARMACOLUUlCAL HASH (ll; Trl {filial-3151l'I‘lC‘S. 10/e
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`Copyright © 2001, 1996, 1990, 1985, 1980, 1975, 1970, 1965, 1955, 1941 by The McGraw-Hill
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`1234567 890 DOWDOW 0987654321
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`ISBN 00741354694
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`This book was set in Times Roman by York Graphic Services, Inc. The editors were Martin I.
`Wonsiewicz and John Mr Morriss; the production supervisor was Philip Galea; and the cover
`designer was Marsha Cohen/Parallelogram. The index was prepared by Irving Condé Tullar and
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`Library of Congress Cataloging-in—Publication Data
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`Goodman and Gilman’s the pharmacological basis of therapeuticsi-IOth edr / [edited by]
`Joel G. Hardman, Lee E. Limbird, Alfred Goodman Gilman.
`p.
`; cm.
`Includes bibliographical references and index.
`ISBN 0—07-135469—7
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`QV 4 G6532 2002]
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`International Edition is not available in North America.
`
`I. Title: Pharmacological basis of therapeutics.
`2. Chemotherapy.
`1. Pharmacology.
`H. Goodman, Louis Sanford
`III. Gilman, Alfred
`IV Hardman, Joel G.
`V. Limbird, Lee E.
`VI. Gilman, Alfred Goodman
`[DNLMz 1. Pharmacology,
`2. Drug Therapy.
`RM300 G644
`2001
`615/.7—d021
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`INTERNATIONAL EDITION ISBN 0—077112432—2
`Copyright © 2001. Exclusive rights by The Mchw-Hill Companies, Inc, for manufacture and export
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`2001030728
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`MYLAN PHARMS. INC. EXHIBIT 1111 PAGE 2
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`

`

`CHAPTER
`
`ADRENOCORTICOTROPIC HORMONE;
`ADRENOCORTICA-L STEROIDS AND
`THEIR SYNTHETIC ANALOGS;
`INHIBITORS OF THE _
`v
`g SYNTHESIS AND ACTIONS OF
`ADRENOCORTICAL
`
`HORMONES
`
`1649
`
`Adrenocorticotmpic hormone (ACTH, also called corticotropin) and the steroid hormone
`products of the adrenal cortex are considered together in this chaptenbecause the ma—
`jor physiological and pharmacological ejfects of ACTH result from its action to increase
`the circulating levels of adrenocortical steroids. Synthetic derivatives of ACTH are used
`principally in the diagnostic assessment of adrenocortical fitnction. As all of the known
`therapeutic effects of ACTH can be achieved with corticosteroids, synthetic steroid hor-
`mones generally are used instead of ACTHfor therapeutic applications.
`Corticosteroids and their biologically active synthetic derivatives dtfier in their
`metabolic (glucocorticoid) and electrolyte—regulating (mineralocorticoid) activities. These
`agents are employed at physiologiCal doses for replacement therapy when endogenous
`"production is impaired. In addition, glucocorticoids are potent suppressors of inflamma-
`tion, and their use in a wide variety of inflammatory and autoimmune diseases makes
`them among the most frequently prescribed classes of drugs. Because they exert efl‘ects
`on almost every organ system, the clinical use of and withdrawal from corticosteroids
`are'complicated by a number of serious side efiects, same of which are life-threatening.
`Therefore, the decision to institute therapy with corticosteroids always requires carefitl
`consideration of the relative risks and benefits in each patient.
`Agents that inhibit various reactions in the steroidogenic pathway and thus alter the
`patterns of secretion of adrenocortical steroids are discussed, as are synthetic steroids,
`such as mtfepristone (see also Chapter 58), that inhibit glucocorticoid action. Agents
`that inhibit the action of aldosterone are presented in'Chapter 29; agents used to inhibit
`growth of steroid—dependent tumors are discussed in Chapter 52.
`
`Bernard P. Schimmer and Keith L. Parker
`
`history. The clinical importance of the adrenal glands was
`first appreciated by Addison, who described fatal outcomes
`in patients with adrenal destruction in a presentation to the
`South London Medical Society in 1849- These studies, pub-
`lished subsequently (Addison, 1855), were soon extended by
`Brown-Séquard, who demonstrated that bilateral adrenalectomy
`was fatal in laboratory animals. It later was shown that the
`adrenal cortex, rather than the medulla, was essential for sur-
`. Vival in these experiments. Further studies demonstrated that the
`adrenal cortex regulated both carbohydrate metabolism and fluid
`
`and electrolyte balance. Efforts by a number of investigators ul-
`timately led to the isolation and characterization of the various.
`adrcnocorticosteroids. Studies of the factors that regulated car—
`bohydrate metabolism (termed glucoconicoids) culminated with
`the synthesis of conisonc, the first pharmacologically effective
`glucocorticoid to be available in large amounts. Subsequently,
`Tate and colleagues isolated and characterized a distinct cor»
`ticostcroid, aldostcmnc,
`that had potent effects on fluid and
`electrolyte balance (and therefore was termed a mineralocor-
`ticoid). The isolation of distinct corticosteroids that regulated
`
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`

`

`1650
`
`SECTION XII HORMONES AND HORMONE ANTAGONISTS
`
`Ser—T r-Ser-Met-
`
`roival-Lys-Va!-Tyr-Pro-Asn-Gly-Ala-Glu-
`Asp-Glu-éeréAlaéGlu-Ala-hh'e-hrmLeuéalu-Phe I
`'
`Figure 60—1. Processing ofPOMC to ACTH and the sequence
`of ACTH.
`
`A schematic overview of the pathway by which pro-opio—
`melanooortin (PQMC) is converted to ACTH and other
`peptides in the anterior pituitary is shown. The light
`blue boxes behind the ACTH structure indicate regions
`identified as important for sucroidogenic activity (residues
`6—40) and binding to the ACTH receptor (15—13). The
`amino acid sequence of human ACTH is shown. LPH,
`lipotropin; MSH, melanocyte—stimulating hormone; PC1,
`prohormone convertase l.
`x.
`
`number of other biologically important peptides, including
`endorphins, lipotropins, and the melanoeyte—stirnulating
`hormones (MSH), also are produced from the same
`prcursor.
`
`Actions on the Adrenal Certex. ACTH stimulates the
`
`adrenal cortex to Secrets glucocorticoids, mineralocorti—
`coids, and weak androgens such as androstenedione and
`dehydroepiandrosterone, which can be converted periph-
`erally into more potent androgens. Based on histological
`analyses, the adrenal cortex originally was separated into
`three zones5the zona glomerulosa, zone fasciculata, and
`20113 reticularis. Functionally, it is more useful to view the
`adrenal cortex as two discrete compartments: the outer
`zona glomerulosa,.which secretes the mineraiocorticoid‘
`aldosterone, and the inner zonae fasciculata/reticularis,
`
`which secrete the gluco'conicoid cOrtisol as well as the
`adrenal androgens (Figure 60—2).7The biochemical basis
`for these differences in steroidogenic output has been de-
`fined in considerable detail. Cells of the outer zone have
`
`receptors for angiotensin II and express aldosterone syn-
`thase, an enzyme that catalyzes the tcrminai reactions in
`mineralocorticoid biosynthesis. In contrast, cells of the in-
`ner zones lack receptors for angiotensin H and express two
`enzymes, steroid 17a-hydroxylase (P45017aland 11f}—
`hydroxylase (P450115),
`that catalyze the production of
`
`_
`
`carbohydrate metabolism or fluid and electrolyte balance ulti—
`mately led to the concept that the adrenal cortex comprises two
`largely independent units: an outer zone that produces mineralo-
`corticoids and an inner region that‘synthesizes glucocorticoids
`and weak androgens.
`Studies of the adrenocortical steroids also played a key
`part in delineating the role of the anterior pituitary» inendocrine
`function. As early as 1912, Cushing described patients with hy—
`percorticism, and later recognized that pituitary basophilism rep-
`resented the cause of the adrenal overactivity (Cushing, 1932),
`thus establishing the link between the anterior pituitary and
`adrenal function. These studies ultimately led to the purifica‘
`tion of ACTH (Astwood et (11., 1952) and the determination of
`its chemical structure. ACTH was further shown to be essential
`in maintaining the structural integrity and steroidogenic capac-
`ity of the inner cortical zones. The role of the hypothalamus in
`pituitary control was established by Harris (1948), who further
`postulated that a soluble factor produced by the hypothalamus
`activated ACTH release. These investigations culminated with
`the determination of the structure of corticotropin—releasing hor»
`mone (CRH), a hypothalamic peptide that regulates secretion of
`ACTH from the pituitary (Vale 3! (IL, 1981).
`Shortly after synthetic cortisone became available, Hench
`and colleagues demonstrated the dramatic effect of glucocorti—
`coids and ACTH in the treatment of rheumatoid arthritis (Hench
`er al., 1949). These studies set the stage for the clinical use
`of corticosteroids in a wide variety of diseases, as discussed
`below.
`
`glucocorticoids.
`
`ADRENOCORTICOTROPIC
`
`HORMONE (ACTH;
`CORTICOTROPIN)
`
`The sequence of human ACTH, a peptide of 39 amino
`acids, 'is shown in Figure 60—1. Whereas removal of a
`single amino acid at the amino terminus considerably im-
`pairs biological activity, a number of amino acids can be
`removed from the carboxy—terminal end without a marked
`effect. The structure—activity relationships of ACTH have
`been studied extensively, and it is believed that a stretch of
`four basic amino acids at positions 15 to 18 is an important
`determinant of high-affinity binding to the ACTH recep-
`tor, whereas amino acids 6 to 10 are important for receptor
`activation (Imura, 1994). As discussed in Chapter 23 and
`' as schematized in Figure 60—1, ACTH is synthesized as
`part of a-1arger precursor protein, pro-opiomelanocortin
`(POMC), and is liberated from the precursor through pro—
`teolytic cleavage at dibasic residues by the enzyme pro-
`hormone convertase 1. Impaired processing of POMC due
`to a mutation in prohormone convertase 1 has been im—
`plicated in the pathogenesis of a human disorder present-
`ing with adrenal insufficiency. lntriguingly, these patients
`also exhibit childhoodobesity, hypogonadotropic hypo~
`gonadism, and diabetes (Jackson et‘ al., 1997), suggesting
`other proteolytic targets for prohormone convertase 1. A
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`

`

`CHAPTER 60 ACTH; ADRENOCORTICAL STEROIDS AND THEIR SYNTEETIC ANALOGS
`
`1651
`
`
`
`“Case.A_1,
`
`1EUR}‘
`
`3;‘_
`Simon
`
`Fasoicdlata/
`Reticularis
`
`Medulla '
`
`Aldosterone
`
`. P45011B
`
`13450170,} 1
`
`Cortisol,
`Androgens
`
`in the gland, it is believed that the actions of ACTH to
`increase steroid hormone production are predominantly
`mediated at the level of de novo biosynthesis. ACTH, like
`most peptide hormones,
`interacts with a specific mem»
`brane receptor. As determined by gene cloning and se-
`quencing, the human ACTH receptor is a member of the
`G protein—coupled receptor family, closely resembling in
`its structure the receptors for melanocyte-stimulating hor-
`mones (Cone and Mountjoy, 1993). ACTH acts through
`the G protein Gs to activate adenylyl cyclase and increase
`intracellular cyclic AMP content. Cyclic AMP is an oblig-
`atory second messenger for most, if not all, effects of
`ACTH on steroidogenesis. Mutations in the ACTH recep—
`tor have been associated with rare syndromes leading to
`familial resistance to ACTH (Clark and Weber, 1998).
`
`lipoid adrenal hyperplasia, a rare
`
`Temporally, the response of adrenocoru'cal cells to ACTH
`has two phases: an acute phase, which occurs within seconds to
`minutes, largely reflects an increased supply of cholesterol sub—
`strate to the steroidogenic enzymes; a chronic phase, Which-oc—
`curs over hours to days, results largely from increased transcrip-
`tion of the steroidogenic enzymes. A summary of the pathways
`of adrenal steroid biosynthesis and the structures of the major
`steroid intermediates and products of the human adrenal cor—
`tex are shown in Figure 60—3. The rate-limiting step in steroid
`hormone production is the conversion of cholesterol to preg—
`nenolone, a reaction catalyzed by the cholesterol side—chain
`cleavage enzyme, designated P450m. Most of the enzymes
`required for steroid hormone biosynthesis, including P450390,
`are members of the cytochrome P450 superfamily, a related
`group of curred-function oxidases that play important roles in
`the metabolism of xenobiotics such as drugs and environmental
`pollutants as Well as in the biosynthesis of such endogenous
`compounds as steroid hormones, vitamin D, bile acids, fatty
`acids, prostaglandins, and biogenic amines (see Chapter I). The
`rate—limiting components in this reaction regulate the mobiliza—
`tion of substrate cholesterol and its delivery to the P450”,
`located in the inner mitochondrial matrix.
`The adrenal cortex uses multiple sources of cholesterol
`to ensure an adequate supply of substrate for steroidogenesis.
`These sources include (i) circulating cholesterol and choles-
`terol esters taken up via the low—densitylipoprotein (LDL)-
`and high-density lipoprotein (HDL)~receptor pathways, (2) lib—
`eration of cholesterol from endogenous cholesterol ester stores
`via-activation of cholesterol esterase, and (3) increased de novo
`biosynthesis.
`The mechanism(s) by which ACTH stimulates the tranle-
`cation of cholesterol to the inner mitochondrial matrix are not
`Well defined. Several candidate mediators of the acute deliv—
`ery of cholesterol
`to the mitochondria have been proposed,
`including a 30,000 dalton phosphoprotein induced by ACTH
`in all primary steroidogenic tissues,
`the peripheral benzodi~
`azepine receptor, and sterol carrier protein-2. The cDNA encod—
`ing the 30,000 dalton phosphoprotein (designated the Steroid-
`ogenic Acute Regulatory Protein, or SLAR) has been cloned and
`shown to activate steroidogenesis (Stocco and Clark, 1996).
`Significantly, mutations in the gene encoding StAR are found
`in patients with congenital
`
`nanaeonnnnn
`Eifisic-"”
`asoncogenes!20
`
`2nU
`5
`
`010‘
`.2112.
`q
`59‘,
`
`'
`
`if“:
`t:
`
`Figure 60-2. The adrenal cortex contains two anatomically
`and functiomlly distinct compartments.
`The majdr functional compartments of the adrenal cor-
`tex are shown, along with .the steroidogenic enzymes that
`determine the unique profiles of corticosteroid products.
`Also shown are the predominant physiologic regulators
`of steroid production: angiotensin II (A II) and K" for
`the zona glomemlosa and ACTH for the zonae fascicu—
`lata/reticularisI
`
`In the absence of the adenohypophysis, the inner
`zones of the cortex atrophy, and the production of glu—
`cocorticoids and adrenal androgens is markedly impaired.
`Although ACTH acutely can stimulate mineralocorticoid
`production by the zona glomerulosa,
`this zone is regu-
`lated predominantly by angiotensin II and extracellular
`K+ (see Chapter 31) and does not undergo atrophy in the
`absence of ongoing stimulation by the pituitary gland. In
`the setting of persistently elevated ACTH, mineralocor—
`ticoid levels initially increase and then return to normal
`(a phenomenon termed ACTH escape).
`Persistently elevated levels of ACTH, due either to
`repeated administration of large doses of ACTH or to flex—
`cessive endogenOus ACTH production, induce hyperplasia
`and hypertrophy of the inner zones of the adrenal cortex,
`with overproduction of cortisol andadrenal androgens.
`Adrenal hyperplasia is most marked in congenital disor-
`ders of steroidogenesis, where ACTH levels are continu-
`ously elevated as a secondary response to impaired cortisol
`biosynthesis.
`
`Mechanism of Action. ACTH stimulates the synthesis
`and release of adrenocortical hormdnes. As specific mech-
`anisms for steroid hormone secretion have not been de~
`fined and since steroids do not accumulate appreciably
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`

`1652
`
`
`Figure 60-3. Pathways of cortigosteroid biosynthesis.
`The steroidogenic pathways used in the biosynthcsis of the corticosteroids are shown, along with the structures of the inicrmediaies and
`products. The pathways that are unique [0 the zona glomerulosa are shown in blue, whereas those unique to the zonac fasciculaia/reticularis
`are shown in gray. P4503”, cholesterol side-chain cleavage enzyme; 3,8-HSD, 3fi~hydroxysteroid dehydrogenase; P450171“ steroid 170!-
`hydroxylase; P450“, steroid 21—hydroxyiase; P4503140, aldostemne synthasc; P450nfl, steroid IXfi—hydroxylase.
`
`H3C
`
`o P
`
`rogesterone
`
`HO
`
`Pregnenolone
`
`Sfi-HSD
`
`|C:
`
`
`
`
`
`
`
`
`
`
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`

`

`CHAPTER 60 ACTH; ADRENOCOR'I‘ICAL STEROIDS AND THEIR SYNTHETIC ANALOGS
`
`Cortisol
`
`Figure 6M._ Overview of the hypotkalamic—pituitmy-adrenal
`(HPA) axis and its bidirectional communication with the im.
`mune system.
`'
`
`The complex regulatory interactions bethen the HPA
`axis and the immune/inflammatory network are shown.
`(-9 indicates a positive regulator. 9 indicates a negative
`regulator:
`IL—l,
`interleukin-1;
`IL—2,
`interleukin-2; IL-6,
`interleukin-6; TN'F-or,
`tumor necrosis factor a; CRH,
`corticotropin—releasing hormone.
`
`stimuli can override these normal negative feedback con—
`trol mechanisms, leading to marked increases in plasma
`concentrations of adrenocortical steroids.
`
`Central Nervous System. The central nervous system (CNS)
`integrates a number of different positive and negative influences
`on ACTH release (Figure 604). These signals converge on the
`CRH neurons, which are clustered largely in the parvocellular
`region of the paraventricular hypothalamic nucleus and make
`axonal connections to the median eminence of the hypothala-
`mus (see Chrousos, 1995, see also Chapter 12). Following re-
`lease into the hypophyseal plexus, CRH is transported via this
`portal system to the pituitary, where it binds to specific mem- .
`brane receptors on corticotropes. Upon CRH binding, the CRH
`receptor activates adenylyl cyclase and increases cyclic AMP
`levels within corticotropcs, ultimater increasing both ACTH
`biosynthesis and secretion. The human CRH receptor has been
`cloned and shown to resemble most closely in sequence the cal-
`citonin/vasoactive intestinal peptide/growth hormone—releasing
`hormone family of G protein—coupled receptors (Chen et al.,
`1993).
`
`Arginine Vasopressin. Arginine vasopressin (AVP) also acts
`as a secretagogue for corticotropes, significantly potentiating
`the effects of CRH. Animal studies have revealed that the po—
`tentiation of CRH action by AVP liker plays a physiologically
`significant role in the full magnitude of the stress response. AVP
`is produced in the parvocellular neurons of the paravenuicuiar
`nucleus,
`like CRH, as well as by magnocellular neurons of
`
`'
`
`congenital disorder in which adrenal cells become engorged
`with cholesterol deposits secondary to an inability to synthesize
`anysteroid hormones (Lin et aL, 1995). This finding points to
`a key role of StAR in the regulated delivery of cholesterol to
`the steroid biosynthetic pathway.
`An important component of the trephic effect of ACTH is
`the enhancement of transcription of the genes that encode the
`individual steroidogem'c enzymes, with associated increases in
`the steroidogenic capacity of the gland. Although the molecular
`mechanisms are still under investigation, it appears that a variety
`of transcriptional regulators mediate the induction of the steroid
`hydroxylases by ACTH (Parker and Schimmer, I995).
`
`In large doses, ACTH
`Extraadrenal Effects of ACTH.
`causes a number of metabolic changes in adrenalectomized
`animals, including ketosis, Iipolysis, hypoglycemia (im-
`mediately after treatment), and resistance to insulin (later
`after treatment}. Because of the large doses of ACTH
`required,
`the physiological significance of these extra-
`adrenal effects is doubtful. ACTH also improves learn—
`ing in experimental animals; this latter effect appears to
`be nonendocrine and mediated via distinct receptors in
`the central nervous system. Patients with primary adrenal
`insufficiency and persistently elevated ACTH levels clas—
`sically are hyperpigmented. This hyperpigmentation prob
`ably results from ACTH activating the MSH receptor on
`the melanocytes, perhaps a consequence of the identity of
`ACTH and MSH in the first 13 amino acids of each of
`their sequences.
`
`p
`
`the supraoptic nucleus; it is secreted into the pituitary plexus
`
`of ACTH Secretion. Hypothalamic-
`Regulation
`Pituitary—Adrenal Axis. The rates of secretion of gluco-
`corticoids are determined by fluctuations in the release of
`' ACTH by the pituitary corticolropes. These corticotropes,
`in turn, are regulated by corticotropin—releasing hormone
`(CRH), a peptide hormone released by CRH neurons of
`the endocrine hypothalamus. These three organs collec-
`tively are referred to as the hypothalamic-pituitary—adrenal
`(HPA) axis, an integrated system that maintains appro-
`'
`‘ priate levels of glucocorticoids (see Figure 60—4 for an
`overview of this axis). There are three characteristic modes
`of regulation ofthe HPA axis: diurnal rhythm in basal
`steroidogenesis, negative feedback regulation by adrenal
`corticosteroids, and marked increases in steroidogenesis
`In response to stress. The diurnal rhythm is entrained by
`higher neuronal centers in response to sleep-wake cycles,
`such that levels of ACTH peak in the early morning hours,
`causing the circulating glucocorticoid levels to peak at ap-
`proximately 8 AM. As discussed below,.ncgative feedback
`regulation occurs at multiple levels of the HPA axis and is
`the major mechanism that operates to maintain circulating
`glucocorticoid levels in the appropriate range. Stressful
`
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`

`1654
`
`SECTION XH HORMONES AND HORMONE ANTAGONISTS
`
`forms of hypoadrenalisrn'due to hypothalamic or pituitary
`disorders. Patients with primary adrenal insufficiency haVe
`high ACTH levels because they lack normal gluco'corti—
`cold feedback inhibition, whereas patients with secondary
`adrenal insufficiency have pituitary or hypothalamic dis-
`ease resulting in low levels of ACTH. The immunoradio—
`metric ACTH assay also is useful in difierentiating be—
`tween ACTH-dcpendcnt and ACTH-independent forms of
`hypercorticism: high ACTH levels are seen when pitu-
`itary adenomas (ta, Cushing’s disease) or nonpituitary
`tumors that secrete ACTH (i.e., ectopic ACTH) underlie
`the hypercorticism, whereas very low ACTH levels are
`seen in patients with excessive glucocorticoid production
`due to primary adrenal disorders. Despite its consider-
`able strengths, one problem with the immunoradiomeuic
`ACTH assay is that its Specificity for intact ACTH can
`lead to false, low values in patients with ectopic ACTH
`secretion; these tumors often secrete aberrantly processed
`forms of ACTH that have biological activity but do not
`react in the antibody assay.
`‘
`
`from the median eminence. After binding to specific G protein—
`coupled receptors of the V“, subtype, AVP activates phospho-
`lipase C, producing diacylglycerol and 1,4,5-inositol trisphos-
`phate as messengers to release ACTH (see Chapters 2 and 12);
`in contrast to CRH, AVP apparently does not increase ACI‘H
`synthesis.
`v
`’
`Negative Iv‘ced'back~ of Glucocarticaids. Glucocorticoids inhibit
`ACTH secretion via direct and indirect actions on CRH neurons
`to decrease CRH mRNA levels and CRH release and via direct
`effects on corticotropes, The effect on CRH release may be
`mediated by specific corticosteroid receptors in the hippocam—
`pus, which are proposed to play important roles in negative
`feedback inhibition exerted by glucocorticoids. At lower corti—
`sol levels, the mineralocorticoid (type I) receptor, which has a
`higher affinity for glucocorficoids and is the predominant form
`found in the hippocampus, is the major receptor species occu-
`pied. As glucocorticoid concentrations rise, the glucocorlicoid
`(type II) receptor also becomes occupied as the capacity of
`the ruineralocorticoid receptor is exceeded. Basal activity of the
`HPA axis apparently is controlled by both classes of receptor,
`whereas feedback inhibition by glucocorticoids predominantly
`involves the glucocorticoid receptor.
`In the pituitary, glucocorticoids act through the glueocorti»
`cold receptor to inhibit the expression of POMC in corticotropes
`as well as‘the release of ACTH. These effects are both rapid
`(occurring within seconds to minutes and possibly mediated by
`glucocorticoid receptor—independent mechanisms) and delayed
`(requiring hours and involving changes in gene transcription
`mediated through the glucocorticoid receptor).
`The Stress Response. Circumstances of stress overcome neg-
`ative feedback regulation of the HPA axis, leading to a marked
`rise in the production of corticosteroids, Examples of stress sig~
`nals include injury, hemorrhage, scvcreinfection, major surgery,
`hypoglycemia, cold, pain, and fear. Although the precise mecha-
`nisms that underlie this stress response and the essential actions
`played by the glucocorticoids are not defined fully, it is clear
`that glucocorticoid secretion is vital for maintaining homeostasis
`in these stressful settings. As discussed below, complex inter-
`actions between the HPA axis and the immune system may be
`a fundamental physiological component of this stress response
`(see Sapolsky et at, 2000; Thrubull and Rivier, 1999).
`
`culating cortisol to levels greater than 18 to 20 rig/d1 indicates
`
`Therapeutic Uses and Diagnostic Applications of
`ACTH. There are anecdotal reports that selected con—
`ditions respond better to ACTH than to corticosteroids
`(e.g., multiple sclerosis), and some clinicians continue to
`advocate therapy with ACTH. Despite this, ACTH cur-
`rently has only limited utility as a therapeutic agent. Ther-
`apy with ACTH is both less predictable and less conve-
`nient than is therapy with appropriate steroids. In addition,
`ACTH stimulates mineralocorticoid and adrenal androgen”
`secretion and may therefore cause acute retention of salt
`and water as well as virilization. While ACTH and the
`corticosteroids are not pharmacologically equivalent, all
`of the known therapeutic effects of ACTH also can be
`achieved with appropriate doses of corticosteroids at a
`lesser risk of side effects.
`
`Testing the Integrity of the HPA Axis. At present, the major
`clinical use of ACTH is in testing the integrity of the HPA axis
`to identify those patients needing supplemental steroid cover—
`age in stressful situations. Other tests used to assess the HPA
`axis include the insulin tolerance test (see Chapter 56) and the
`metyrapone test (discussed later in this chapter). ACTH puri—
`fied from animal pituitary glands is available in long—lasting
`injectable gel preparations as a gelatin solution (ELF. ACHIAR
`GEL; 40 or SOTO/vial}. Cosyntropin (conmosru) is a synthetic
`peptide that corresponds to residues 1 to 24 of human ACTH.
`At the considerably supraphysiological dose of 250 ug, cosyn-
`tropin maximally stimulates adrenocortical steroidogenesis. In
`the rapid cosyntropin stimulation test, 250 pg of. cosyntropin is
`administered either intramusculme or intravenously, with cor—
`6501 measured just before administration (baseline) and 30 to
`60 minutes after cosyntropin administration. An increase in cir—
`
`Initially, ACTH levels were mea-
`Assays for ACTH.
`sured by bioassays that measured induced steroid produc-
`tion or the depletion of adrenal ascorbic acid; such assays
`have been used to standardize ACTH amounts in differ-
`ent preparations used for both diagnostic and therapeutic
`purposes. Radioirnmunoassays were developed to quan-
`titate ACTH levels in individual patients, but they were
`not always reproducible, and their sensitivity did not al-
`ways clearly differentiate between low and normal levels
`
`of the hormone. An irnrnunoradiometric assay, which re-
`liably measures ACTH levels, is now widely available.
`This assay, which uses two separate antibodies directed at
`distinct epitopes on the ACTH molecule, considerablyin—
`creases the ability to differentiate between primary hypo-
`adrenalism due to intrinsic adrenal disease and secondary
`
`DEF-ABIRA-0000472
`
`MYLAN PHARMS. INC. EXHIBIT 1111 PAGE 8
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`

`

`a normal response (others also have included an increase of
`7 [Lg/d1 over the baseline value as a positive reSponse, although
`this is less widely accepted). In patients with pituitary or hy—
`pothalamic diseaseof recent onset or shortly after surgery for
`pituitary tumors, this standard cosyntropin stimulation test may
`be misleading, as the duration of ACTH deficiency may have
`been insufficient to cause significant adrenal atrophy with frank
`loss of steroidogenic capacity. For this latter group of patients,
`some experts advocate a “low-dose” cosyntropln stimulation
`test, in which 1 tag of cosyntropin is administered intravenously,
`with cortisol measured just before and 30 minutes after cosyn—
`tropin administration (Abdu et al., 1999). Because cosyntropin
`is not generally available in a l-rtg dose, the standard ampoule
`of cosyntropin (250 gig) is diluted to permit accurate delivery
`of the l—ptg challenge dose, with the cutoff for a normal re-
`sponse being the same as that for the standard test. Care must
`be taken to avoid adsorption of the ACTH to plastic tubing and
`to measure the plasma cortisol precisely at 30 minutes after the
`cosyntropin injection. Although some studies indicate that the
`low-dose test is more sensitive than the standard ZSO—ug test.
`others report that
`this test also may fail
`to detect secondary
`adrenal insufficiency.
`As noted above, primary and secondary adrenocortical dis-
`eases are reliably distinguished using currently available sensi-
`tive assays for ACTH. Thus, longer-course ACTH stimulation
`tests rarely are used to differentiate between these disorders.
`CRH Stimulation Test. Ovine CRH, also termed carticorelin
`(ACTHREL), is available for diagnostic testing of the HPA axis.
`In patients with documented ACTH~dependent hypercorticism,
`CRH testing may help differentiate beIWeen a pituitary source
`(i.e., Cushing’s disease) and an ectopic source of ACTH. After
`two baseline blood samples are obtained fifteen minutes apart,
`corticorelin (1 lag/kg) is administered intravenously over a 30—
`to 60—second interval, and blood samples are obtained at 15, 30,
`and 60 minutes for ACTH measurement. It is important that the
`blood samples be handled as recommended for the ACTH as
`say. At the recommended dose, CRH generally is well tolerated,
`although flushing may occur, particularly if the dose isladmin»
`istered as a bolus. Patients with Cushing‘s disease respond to
`CRH with either a norn‘ral or an exaggerated increase in ACTH,
`whereas ACTH levels do not increase in patients with ectopic
`sources of ACTH. It should be noted that’this test is not per~
`feet: ACTH levels are induced by CRH in occasional patients ‘
`with ectopic ACTH, whereas approximately 5% to 10% of pa-
`tients with Cushingjs disease fail to respond. To improve the
`diagnostic accuracy of the CRH stimulation test, some authori—
`
`Wm
`
`ORTISOL ALDOSTERONE
`Rate of secretion under
`
`optimal conditions
`
`Concentration in peripheral plasma:
`8 A.M.
`’ 4 PM.
`
`10 rug/day
`
`0.125 mg/day
`
`16 ,ng/IDO ml
`4 rag/100 ml
`
`0.01 rig/100 ml
`0.01 [Lg/100 ml
`
`CHAPTER 60' ACTH; ADRENOCORTICAL STEROIDS AND THEIR SYNTHETIC ANALOGS
`
`1655
`
`ties advocate sampling of blood from the inferior petrosal sinus
`following peripheral administration of CRH. When performed
`by a skilled neuroradiologist, this procedure may increase diag—
`nostic accuracy with a tolerable risk of complications from the
`catheterization procedure.
`-
`
`Absorption and Fate. ACTH is readily absorbed from par-
`enteral sites. The hormone rapidly disappears from the circula-
`tion following intravenous administration; in human beings, the
`half-life in plasma is about 15 minutes, primarily due to rapid
`enzymatic hydrolysis.
`
`Toxicity of ACTH. Aside from rare hypersensitivity reactions,
`the toxicity of ACTH is primarily attributable to the increased
`secretion of corticosteroids. Cosyntropin is generally less anti-
`genic than native ACTH. Moreover, ACTH isolated from animal
`pituitaries contains significant amounts of vasopressin, which
`can lead to life—threatening hyponatremia. These factors make
`cosyntropin the preferred agent for clinical use.
`
`ADRENOCORTICAL STEROIDS
`
`The adrenal cortex synthesizes two classes of steroids: the
`corticosteroids (glucocorticoids and mineralocorticoids),
`which have 21 carbon atoms, and the androgens, which
`have 19 (Figure 60—3). The actions of corticosteroids his-
`torically Were described as glucoco