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TABLE 10.2 Response of the Major Vascular Beds to Usual Doses of the Catecholamines

Vascular bed

Receptor type*

Norepinephrine

Epinephrine

Isoproterenol

Cutaneous blood vessels

a

Constriction

Constriction

None

Visceral blood vessels

a

Constriction

Constriction

None (weak dilation)

Renal blood vessels

a

Constriction

Constriction

None (weak dilation)

Coronary blood vessels

a, ß

Dilation

Dilation

Dilation

Skeletal muscle blood vessels

a, ß2

Constriction

Dilation

Dilation

Pial blood vessels

a, ßt

Constriction/dilation

Constriction/dilation

Dilation

*While virtually all blood vessels have (^-receptors, some also have a2-receptors. Stimulation of either subtype generally results in vasoconstriction.

*While virtually all blood vessels have (^-receptors, some also have a2-receptors. Stimulation of either subtype generally results in vasoconstriction.

tion on these blood vessels because of its high affinity for both a- and ^-adrenoceptors. Whether epinephrine produces vasodilation or vasoconstriction in skeletal muscle depends on the dose administered. Low doses of epinephrine will dilate the blood vessels; larger doses will constrict them.

Although several factors can influence the flow of blood through the coronary vessels, the most important of these is the local production of vasodilator metabolites that results from stimulation-induced increased work by the heart. a-Adrenoreceptors and p-adrenoceptors in the coronary vascular beds do not play a major role in determining the vasodilator effects of the administration of epinephrine or norepinephrine.

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