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(also angiotonin, or angiotensin), a biologically active substance that increases blood pressure. Hyper-tensin is a polypeptide consisting of several amino acids. It is formed from a hypertensinogen that is present in blood plasma when the blood supply to the kidneys is insufficient. It is a component part of the renin-angiotensin system, which participates in regulating vascular tone. Analogues of natural hypertensin have been synthesized that are as active as it is.