section 31.2
Pituitary Gland (Hypophysis)
F I G U R E 3 1 - 6
Structure of hum an prolactin. [Reproduced w ith perm ission from R. K. M urray, D. K. Granner, R A. M ayes, and
V. W. Rodw ell,
H a r p e r ’s B io ch em istry,
21st ed. Norwalk: A ppleton & Lange, 1988. © 1 9 8 8 A ppleton & Lange.]
GH production or responsiveness. Thus, a GH deficiency
results in IGF-I deficiency, whereas a GH excess results in
IGF-I excess. GH deficiency in children results in reduced
growth velocity and growth retardation (dwarfism) due to
secondary IGF-I deficiency, whereas in adults there are no
dramatic signs or symptoms. Adults who are deficient pri-
marily in GH have decreased lean body mass, increased
adiposity, and are at increased risk of cardiovascular
GH hypersecretion in children causes increased growth
rate and can result in
However, GH excess
occurs infrequently in childhood, and most frequently
in middle-aged adulthood, which leads to
= extremities +
= large), a condition in
which the cartilaginous tissues proliferate, resulting in
distorted overgrowth of the hands, feet, mandibles, nose,
brow, and cheek bones. Because epiphyseal cartilage is ab-
sent in long bones, there is no gain in height. Acromegaly
promotes insulin resistance and cardiovascular complica-
tions. Resistance to the effects of GH results in a condition
similar to GH deficiency. The major cause of GH resis-
tance is a genetic defect in the growth hormone receptor
(GHR) and the resultant condition is known as
This is an autosomal recessive disorder char-
acterized by normal to high levels of serum growth hor-
mone and low levels of IGF-I. Analysis of the GHR gene
in Laron-type dwarfism has shown point mutations, dele-
tions, and splicing defects.
Growth hormone deficiency in children can be treated
by administration of recombinant GH or, in some cases,
growth hormone-releasing hormone. Potential targets for
recombinant GH that are undergoing clinical investiga-
tion include children with idiopathic short stature, persons
with wasting syndrome associated with human immunod-
eficiency virus infection, critically ill patients, and elderly
Excess production of GH due to somatotroph adeno-
mas may be treated by surgical resection, irradiation, or in
some cases with somatostatin analogues (e.g., octreotide)
that suppress GH secretion, or by a combination of these
Human prolactin (PRL) contains 199 amino acid residues
(M.W. 23,500) and three intramolecular disulfide bridges
(Figure 31-6). In healthy adults the anterior pituitary re-
leases very little PRL under nonstressed conditions, pri-
marily because PRL release is under hypothalamic inhibi-
tion. This inhibition is exerted by dopamine or PIH. The
hypothalamus also secretes PRF but the major regulator
appears to be PIH.
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