DƯỢC LÍ Goodman & Gilman's The Pharmacological Basis of Therapeutics 12th, 2010

Table 8–1
Responses of Effector Organs to Autonomic Nerve Impulses (Continued)
ADRENERGIC
CHOLINERGIC
RECEPTOR PARASYMPATHETIC RECEPTOR
ORGAN SYSTEM SYMPATHETIC EFFECT a SUBTYPE b EFFECT a SUBTYPE b
Autonomic Nerve
Endings
Sympathetic terminal
Autoreceptor Inhibition of NE release α 2A
> α 2C
(α 2B
)
Heteroreceptor — Inhibition of NE release M 2
, M 4
Parasympathetic
terminal
Autoreceptor — — Inhibition of ACh release M 2
, M 4
Heteroreceptor Inhibition ACh release α 2A
> α 2C
— —
a
Responses are designated + to +++ to provide an approximate indication of the importance of sympathetic and parasympathetic nerve activity in the
control of the various organs and functions listed.
b
Adrenergic receptors: α 1
, α 2
and subtypes thereof; β 1
, β 2
, β 3
. Cholinergic receptors: nicotinic (N); muscarinic (M), with subtypes 1-4. The receptor
subtypes are described more fully in Chapters 9 and 12 and in Tables 8–2, 8–3, 8–6 and 8–7. When a designation of subtype is not provided, the
nature of the subtype has not been determined, unequivocally. Only the principal receptor subtypes are shown. Transmitters other than ACh and NE
contribute to many of the responses.
c
In the human heart, the ration of β 1
to β 2
is about 3:2 in atria and 4:1 in ventricles. While M 2
receptors predominate, M 3
receptors are also present
(Wang et al., 2004).
d
The predominant α 1
receptor subtype in most blood vessels (both arteries and veins) is α 1A
, although other α 1
subtypes are present in specific blood
vessels. The α 1D
is the predominant subtype in the aorta (Michelotti et al., 2000).
e
Dilation predominates in situ owing to metabolic autoregulatory mechanisms.
f
Over the usual concentration range of physiologically released circulating epinephrine, the β receptor response (vasodilation) predominates in blood
vessels of skeletal muscle and liver; β receptor response (vasoconstriction) in blood vessels of other abdominal viscera. The renal and mesenteric
vessels also contain specific dopaminergic receptors whose activation causes dilation.
g
Sympathetic cholinergic neurons cause vasodilation in skeletal muscle beds, but this is not involved in most physiological responses.
h
The endothelium of most blood vessels releases NO, which causes vasodilation in response to muscarinic stimuli. However, unlike the receptors
innervated by sympathetic cholinergic fibers in skeletal muscle blood vessels, these muscarinic receptors are not innervated and respond only to
exogenously added muscarinic agonists in the circulation.
i
While adrenergic fibers terminate at inhibitory β receptors on smooth muscle fibers and at inhibitory β receptors on parasympathetic (cholinergic)
excitatory ganglion cells of the myenteric plexus, the primary inhibitory response is mediated via enteric neurons through NO, P2Y receptors, and
peptide receptors.
j
Uterine responses depend on stages of menstrual cycle, amount of circulating estrogen and progesterone, and other factors.
k
Palms of hands and some other sites (“adrenergic sweating”).
l
There is significant variation among species in the receptor types that mediate certain metabolic responses. All three β adrenergic receptors have
been found in human fat cells. Activation of β 3
receptors produces a vigorous thermogenic response as well as lipolysis. The significance is unclear.
Activation of β receptors also inhibits leptin release from adipose tissue.
over the entire body are affected simultaneously. Heart
rate is accelerated; blood pressure rises; red blood cells
are poured into the circulation from the spleen (in certain
species); blood flow is shifted from the skin and
splanchnic region to the skeletal muscles; blood
glucose rises; the bronchioles and pupils dilate; and the
organism is better prepared for “fight or flight.” Many
of these effects result primarily from or are reinforced
by the actions of epinephrine secreted by the adrenal
medulla (described later). In addition, signals are
received in higher brain centers to facilitate purposeful
responses or to imprint the event in memory.
The parasympathetic system is organized mainly
for discrete and localized discharge. Although it is
concerned primarily with conservation of energy and
maintenance of organ function during periods of minimal
activity, its elimination is not compatible with
life. Sectioning the vagus, e.g., soon gives rise to pulmonary
infection because of the inability of cilia to
remove irritant substances from the respiratory tract.
The parasympathetic system slows the heart rate,
lowers the blood pressure, stimulates GI movements
and secretions, aids absorption of nutrients, protects
the retina from excessive light, and empties the urinary