Abstract
THE mammalian adrenal gland consists of two anatomically distinct regions; the inner medulla composed largely of catecholamine-producing chromaffin cells, and the outer cortex containing cells that secrete steroid hormones. Although these two adrenal components are derived from different primary germ layers, they come into close contact during embryonic life through an unusual process of tissue migration. Adrenaline is formed in the adrenal medulla through the N-methylation of noradrenaline1. This process is catalysed by an enzyme, phenylethanolamine-N-methyl transferase (PNMT), which is highly concentrated in adrenal chromaffin cells2 and also present in several areas of the brain3. PNMT activity is stimulated in the rat4–6 and the dog7 by hormones secreted from the anterior pituitary gland and the adrenal cortex.
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