Adrenal Medullary Hormones
المؤلف:
Marcello Ciaccio
المصدر:
Clinical and Laboratory Medicine Textbook 2021
الجزء والصفحة:
p356-357
2025-10-05
71
The chromaffin cells of the adrenal medullary synthesize, accumulate, and release the catecholamine hormones: dopa mine, norepinephrine, and adrenaline (epinephrine) (Fig. 1); of these, adrenaline represents the primary product of the adrenal medullary (80%) and the only one synthesized exclusively in the adrenal.
Fig1. Synthesis of catecholamines. (Copyright EDISES 2021. Reproduced with permission)
Adrenaline circulates bound to albumin or another low- affinity protein.
Catecholamines are released into the circulation in response to physical or emotional stress and mediate their biological action through interaction with α (α1, α2) and β (β1, β2, β3) adrenergic receptors; biological effects vary based on the receptor bound.
Endogenous catecholamines are involved in regulating cardiovascular function and circulatory hemodynamics. In particular, they mediate nervous control of vasomotor tone, influencing peripheral resistance; moreover, they have inotropic (increase in contractile force of cardiac muscle) and positive chronotropic (increase in heart rate) effects. Other effects of catecholamines unrelated to hemodynamics include stimulation of hepatic glycogenolysis and peripheral lipolysis, mydriasis, slowing of intestinal motility, uterine contractions and relaxation, and bronchodilation. The combined action on the cardiovascular function and the energetic substrates is related to the possibility of reacting in emergencies. Adrenaline is, by definition, the hormone of stress and fear (β-adrenergic effects).
Catabolism of catecholamines begins with degradation by the enzymes catechol-O-methyltransferase (COMT) and monoamine oxidase (MAO), which form inactive O-methylated and deaminated metabolites that are further modified by conjugation with glucuronic or sulfuric acid before being excreted renally. The primary catecholamine metabolites are metanephrine (derived from adrenaline), normetanephrine (derived from norepinephrine), and vanillyl mandelic acid (derived from norepinephrine and adrenaline). A minimal amount of adrenaline and noradrenaline (<5%) is excreted directly in the urine.
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