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INTRODUCTION

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Vasoactive peptides are autacoids with significant actions on vascular smooth muscle as well as other tissues. They include vasoconstrictors, vasodilators, and peptides with mixed effects. Antagonists of these peptides or the enzymes that produce them have useful clinical properties.

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In addition to their actions on smooth muscle, many vasoactive peptides also function as neurotransmitters and local and systemic hormones. The most important vasoactive peptides include angiotensin, bradykinin, natriuretic peptides, calcitonin gene-related peptide (CGRP), endothelins, neuropeptide Y (NPY), substance P and vasoactive intestinal peptide (VIP) (discussed in this chapter), and vasopressin (Chapters 15 and 37). Many other endogenous peptides with very important actions (eg, insulin, glucagon, opioid peptides) have less or no direct vascular smooth muscle effects.

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Vasoactive peptides probably all act on cell surface receptors. Most act via G protein-coupled receptors and cause the production of well-known second messengers (Table 17–1); a few may open ion channels.

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Table Graphic Jump Location
TABLE 17–1Some vasoactive peptides and their properties.
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ANGIOTENSIN & ITS ANTAGONISTS

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A. Source and Disposition
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Angiotensin I is produced from circulating angiotensinogen by renin, an enzyme released from the juxtaglomerular apparatus of the kidney. Angiotensin I is an inactive decapeptide, and is converted into angiotensin II (ANG II, also denoted AII), an active octapeptide, by angiotensin-converting enzyme (ACE), also known as peptidyl dipeptidase or kininase II (see Figure 11–3). Angiotensin II, the active form of the peptide, is rapidly degraded by peptidases (angiotensinases).

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B. Effects and Clinical Role
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ANG II is ...

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