section 31.2
Pituitary Gland (Hypophysis)
745
TABLE 31-7
Glycoprotein Family
Hormone
Site of
Secretion
Peptide
Length
Location
of Gene
Carbohydrate
(%)
Function
Regulation
of Secretion
Thyroid-
Stimulating
Hormone
(TSH)
(Thyrotropin)
Anterior Pituitary
(Thyrotroph)
TSHa = 89 aa
6q21.1-23
16.2
(
1
% sialic acid)
Stimulates thyroid
growth and function.
Stimulated by
TRH and
inhibited by
thyroid hormone
and somatostatin.
TSH0= 112 aa
lp
2 2
Luteinizing
Hormone
(LH)
Anterior Pituitary
(Gonadotroph)
LHa = 89 aa
6q21.1-23
15.7
(
1
% sialic acid)
Stimulates
steroidogenesis in
gonads.
Stimulated by
GnRH and
inhibited by
estrogen.
LHß=l
1 2
aa
19q 12.32
Follicle-
Stimulating
Hormone
(FSH)
Anterior Pituitary
(Gonadotroph)
FSHa = 89 aa
6q21.1-23
18.2
(5% sialic acid)
Stimulates
gametogenesis and
estrogen formation
ingonads.
Stimulated by
GnRH and
inhibited by
estrogen.
FSHjS = 115 aa
llpl3
Chorionic
Gonadotropin
(hCG)
Placenta
(Syncytiotro-
phoblast)
hCGa = 89 aa
6q21.1-23
31.0
(
1 2
% sialic acid)
Stimulates
steroidogenesis in
gonads and placenta.
Autocrine?
hCG/3 = 112 aa
19ql3.32
does not release TSH in response to cold exposure; only
during infancy is TSH released in humans in response
to cold. In the normal adult, the pituitary contains about
0.3 mg TSH, and the basal level of the hormone in blood
is about 1 ng/mL (see also Chapter 33).
Luteinizing hormone
(LH) and
follicle stimulating
hormone
(FSH) are synthesized within the same go-
nadotrophs but are products of different genes. They dif-
fer in carbohydrate composition (and thus in clearance
rates); although their /3 subunits have the same number of
amino acid residues, they differ in amino acid sequences.
In normal men and in women whose menstrual periods
are regular, the pituitary contains about 0.08 mg LH and
about 0.04 mg FSH. In postmenopausal women, the levels
are about 2.5 times higher. The regulation of the release
of LH and FSH and the functions of these hormones are
discussed in Chapter 34.
Neural Regulation of Anterior Pituitary Function
Superimposed upon the fine-tuned regulation of ante-
rior pituitary hormone release by the hypothalamic hy-
pophysiotrophic hormones and by circulating substances
is the coarse-tuned regulation by the CNS, which con-
veys the need for a large adjustment in hormone out-
put. These CNS signals arise from different regions of
the brain and influence one or more of the pituitary hor-
mones via different hypothalamic nuclei. Some signals
result from CNS programming in relation to circadian
rhythms, some are psychogenic, and some are sensory
inputs from exteroceptors (sight, sound, smell) and in-
teroceptors (e.g., cardiovascular disturbances) and repre-
sent the afferent limbs of a neuroendocrine reflex. They
affect pituitary hormone secretion and also, via the pe-
ripheral nerves, that of the adrenal medulla. As a rule, the
release of a hormone in response to coarse tuning of the
CNS is of high amplitude and stimulus-coupled, lasting
only as long as the stimulus is applied. It generally over-
rides the fine-tuning, negative-feedback effect of periph-
eral hormones or blood substrates, unless these levels are
abnormally elevated. The means by which the CNS influ-
ences the activity of the anterior pituitary are presented in
Table 31-8. For purposes of comparison and to emphasize
that the pituitary is not the only endocrine gland affected
by neurogenic signals, the adrenal medulla and the neuro-
hypophysis are included in the table.
“Stress” refers to any stimulus that can arouse the auto-
nomic nervous system. It may be pleasurable or disturbing,
or it may involve actual perception of pain or the anticipa-
tion of it. The nature of the stress appears to be important
in the stress-induced release of ACTH (and cortisol), GH,
and PRL, since these hormones are released in response to
noxious stimuli (unpleasant or painful) that are relatively
novel, unfamiliar, or unexpected. ACTH is released most
readily (lowest threshold), while PRL is the least respon-
sive. The intensity of the stress appears to be important
