Page 272 - Color Atlas Of Pathophysiology (S Silbernagl Et Al, Thieme 2000)

Somatotropin
Somatotropin (growth hormone [GH]) is oxygen delivery will result (angina pectoris;
formed in the anterior lobe of the pituitary → p. 218). Arterial hypertension occurs rela-
gland. It inhibits the uptake of glucose in fat tively frequently (in 30% of cases). Thickening
and muscle cells and promotes lipolysis, gluco- of the skin is associated with increased sweat
neogenesis, collagen synthesis, and the forma- and sebum production. Compression of the
tion of erythropoietin (in part through the me- median nerve can lead to carpal tunnel syn-
diation of hepatic somatomedins or insulin- drome. Decreased glucose uptake in peripher-
like growth factors [IGF], e.g., IGF-1). Somato- al cells favors the development of hyper-
tropin stimulates the enteric absorption of cal- glycemia (→ A4), in some cases of diabetes
cium and phosphates as well as the renal ex- mellitus. Increased intestinal absorption re-
cretion of calcium. It also promotes bone sults in calcium excess followed by hypercal-
growth (before the end of epiphyseal fusion ciuria (→ A5). The latter may cause precipita-
and thus longitudinal growth) as well as soft tion of calcium salts in urine (nephrolithiasis;
tissue growth. Somatotropin promotes T-cell → p.120). Somatotropin excess also promotes
proliferation, interleukin 2 (IL-2) formation the development of tumors.
A somatotropin-producing pituitary tumor
and the activity of natural killer cells, cytotoxic often causes enlargement of the sella turcica;
Hormones strengthens immune defense. Estrogens inhib- pressure on the optic chiasma (→ A6) can give
T cells, and macrophages. In this way it
rise to visual field defects (typically bitemporal
it the formation of somatomedins and thus
The normally pulsatile liberation of somato-
ing blinkers; → p. 326). Displacement of other
9 also reduce the effects of somatotropins. hemianopia, as though the patient were wear-
tropin is regulated by the hypothalamic mes- endocrine cells can lead to gonadotropin defi-
senger substances somatoliberins (somato- ciency, and thus to amenorrhea as well as loss
crinin) and somatostatin (inhibitory). The re- of libido, and impotence (→ A7). Conversely,
lease of somatotropin is stimulated by amino somatotropin-producing tumors can also re-
acids, hypoglycemia, glucagon, dopamine, and lease other hormones, such as prolactin (→
stress. Hyperglycemia, hyperlipidacidemia, p. 260).
obesity, and cold inhibit its release. Somatotropin deficiency can be genetically
An excess of somatotropin is usually due to determined or due to damage of the hormone-
uncontrolled formation of the hormone, for ex- producing cells (e.g., tumor, hemorrhage, radia-
ample, by a pituitary adenoma or, in rare cases, tion), decreased hypothalamic stimulation, or
by an ectopic tumor. Increased stimulation of an inibition of release (cortisol, hypothyroid-
hormone synthesis by somatoliberin is equally ism). The effect of somatotropin can also be
rare. Finally, uncontrolled therapeutic adminis- weakened by estrogens. If somatotropin defi-
tration of somatotropin can also result in an ciency occurs before epiphyseal fusion, pitui-
iatrogenic excess of somatotropin (→ A1). tary dwarfism will result. However, a deficien-
Massive somatotropin excess before epiph- cy that occurs after the completion of longitu-
yseal fusion is completed leads to gigantism dinal growth will have no visible effect. Never-
(height up to 2.6 m). In adults it results in acro- theless, decreasing release of somatotropin in
megaly (enlarged cheek bones, mandibula, the elderly probably contributes to a weaken-
feet and hands, and supraorbital bulge), carti- ing of the immune system.
lage hypertrophy with arthropathy and calcifi-
cation of cartilage and intervertebral disks
(→ A2). At the same time there is an increase
in the size of soft tissues, for example, tongue,
heart, liver, kidneys, thyroid, salivary glands,
and skin (→ A3). This increase in organ size
can lead to further complications. If, for exam-
262 ple, vascularization does not increase with
myocardial hypertrophy, impaired coronary
Silbernagl/Lang, Color Atlas of Pathophysiology © 2000 Thieme
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