Renin enzyme action

Renin assays can be useful in distinguishing between primary and secondary aldosteronism. It can be measured by its enzymic action on angiotensinogen, the product, angiotensin I, being measured by radioimmunoassay. 

Sites of action of drugs that interfere with the renin-angiotensin-aldosterone system. ACE, angiotensin-converting enzyme ARBs, angiotensin receptor blockers. 

Although Ang I contains the peptide sequences necessary for all of the actions of the renin-angiotensin system, it has little or no biologic activity. Instead, it must be converted to Ang II by converting enzyme (Figure 17-1). Ang I may also be acted on by plasma or tissue... 

Kinins are potent vasodilator peptides formed enzymatically by the action of enzymes known as kallikreins or kininogenases acting on protein substrates called kininogens. The kallikrein-kinin system has several features in common with the renin-angiotensin system. 

Under the proper stimulus renin is released into the circulating blood where it can be identified, especially in that from the renal vein. It acts rapidly upon its specific substrate, splitting the protein into peptides, one or more of which have been called hypertensin or angiotonin. Hypertensin has been concentrated but not obtained in pure form. It is the effector substance of renin, constricting arterioles and raising blood pressure. The action of hypertensin is abolished by hypertensinase, an enzyme found in blood and renal extracts. Fortunately, the latter is destroyed by heat and alkalinity. 

Amine oxidase also was found to have the ability of diminishing or abolishing the pressor action of renin. When an active preparation of the enzyme was injected intravenously into rats, subsequent injections of renin had little effect (Figures 4 and 5). Hypertensin, however, showed only a modified response in these preparations, probably because of the relative slowness of action of the enzyme. Similar results were found with other pressor agents. 

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