Adrenal Glands: Catecholamins
References: (Benninghoff, 1993).
Biosynthesis of Catecholamins
The amino acid phenylalanine is the precursor of all catecholamins, they are synthesized via the following steps: tyrosine, dopa, dopamine, norepinephrine and epinephrine. The rate-limiting enzyme is tyrosine hydroxylase, which catalyzes the conversion of phenylalanine into tyrosine and dopa.
Effects of catecholamins
Adrenaline acts on alpha-1, beta-1 and beta-2 receptors. Noradrenaline acts mainly on alpha-1 receptors, rather than the beta-1 receptors. Dopamine acts in small doses on the dopamine receptor DA 1 and 2, in higher doses on alpha-1 receptors.
- Alpha-1 receptors: vasoconstriction, smooth muscle contraction of the bladder neck, glycogenesis.
- Alpha-2 receptors: vein constriction, central attenuation of the sympathetic nervous system, inhibition of insulin release, relaxation of the intestine, preventing lipolysis.
- Beta-1 receptors: positive inotropic and positive chronotropic to the heart, lipolysis, renin release.
- Beta-2 receptors: bronchodilation, vasodilation, gluconeogenesis, relaxation of the uterus, relaxation of the intestine.
- DA1 receptors: vasodilation.
- DA2 receptors: Prevent noradrenaline release (presynaptic).
Metabolism of Catecholamines
The plasma half-life of epinephrine is around 20 s. The inactivation of adrenaline depends mainly on the monoamine oxidase (MAO) and catecholamine-O-methyltransferase (COMT). The metabolic products are vanillylmandelic acid, metaadrenalin and metanoradrenalin; they are excreted via the urine. Furthermore, catecholamins are inactivated via re-uptake and re-used as neurotransmitters.
Index: 1–9 A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
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Benninghoff 1993 BENNINGHOFF, A.:
- Makroskopische Anatomie, Embryologie und Histologie des
München; Wien; Baltimore : Urban und Schwarzenberg, 1993