3,4-Dihydroxy-phenylglycol (DHPG)

figure 11-9 Catabolism of catecholamines in the blood and of norepinephrine in nerve endings. (A) The main site of catabolism of circulating epinephrine and norepinephrine is the liver. The conjugates formed there are mostly glucuronides and sulfates. (B) Catabolism of norepinephrine in adrenergic nerve endings. The acid and glycol enter circulation and may be subsequently O-methylated in VMA and in 3-methoxy-4-hydroxyphenylglycol. Abbreviations: MAO, monoamine oxidase; COMT, catechol O-methyltransferase; MHPG, monohydroxyphenylglycol. Reproduced from Ganong W. F. (1995). "Review of Medical Physiology," 17th ed., p. 92. Lange Medical Publications, Los Altos, California.

TABLE 11-3 Responses of Effector Organs to Autonomic Nerve Impulses and Circulating Catecholamines"

Effector organs

Cholinergic impulse response

Receptor type'

Noradrenergic impulses Response


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