A hypotensive peptide, neurotensin, has been isolated from bovine hypothalamus. The peptide, identified as a tridecapeptide composed of Lys, Arg₂, Asx, Glx₂, Pro₂, Ileu, Leu₂, and Tyr₂, was purified using column chromatography and paper electrophoresis. It lacks a free NH₂-terminus but has a free COOH terminus that can be acted upon by carboxypeptidase A. Neurotensin induces hypotension in rats and can stimulate contraction of guinea pig ileum and rat uterus, but relaxes the rat duodenum. These properties classify it as a "kinin," though its chemical composition differs from known peptides. During the purification of substance P, a different peptide was detected that caused vasodilation and hypotension in anesthetized rats. This peptide, named neurotensin, was isolated in pure form and characterized. Its amino acid composition and molecular weight were determined, and its biological activity was assessed. Neurotensin's effects on vascular permeability and contractility were also studied. Neurotensin was found to lack a free NH₂-terminus, as evidenced by DNS-chloride treatment and enzymatic digestion. It has a free COOH terminus, which is released by carboxypeptidase A. Neurotensin induces vasodilation and hypotension, with effects dependent on dose. It also increases vascular permeability, causing edema and leakage of albumin-bound dye. Neurotensin's biological activity is not affected by hypophysectomy, suggesting a role beyond the pituitary. It may function as a neurohormone, acting on peripheral targets via neurovascular pathways. Its effects on smooth muscle preparations indicate it can stimulate contraction in some tissues and relax in others. The peptide's physiological function remains unclear, but its presence in the hypothalamus suggests a potential role in neural signaling or modulation of nervous activity. Neurotensin's unique properties, including its hypotensive effects and acute tachyphylaxis, distinguish it from other known peptides. Its role in vascular regulation and inflammatory responses is also under investigation.A hypotensive peptide, neurotensin, has been isolated from bovine hypothalamus. The peptide, identified as a tridecapeptide composed of Lys, Arg₂, Asx, Glx₂, Pro₂, Ileu, Leu₂, and Tyr₂, was purified using column chromatography and paper electrophoresis. It lacks a free NH₂-terminus but has a free COOH terminus that can be acted upon by carboxypeptidase A. Neurotensin induces hypotension in rats and can stimulate contraction of guinea pig ileum and rat uterus, but relaxes the rat duodenum. These properties classify it as a "kinin," though its chemical composition differs from known peptides. During the purification of substance P, a different peptide was detected that caused vasodilation and hypotension in anesthetized rats. This peptide, named neurotensin, was isolated in pure form and characterized. Its amino acid composition and molecular weight were determined, and its biological activity was assessed. Neurotensin's effects on vascular permeability and contractility were also studied. Neurotensin was found to lack a free NH₂-terminus, as evidenced by DNS-chloride treatment and enzymatic digestion. It has a free COOH terminus, which is released by carboxypeptidase A. Neurotensin induces vasodilation and hypotension, with effects dependent on dose. It also increases vascular permeability, causing edema and leakage of albumin-bound dye. Neurotensin's biological activity is not affected by hypophysectomy, suggesting a role beyond the pituitary. It may function as a neurohormone, acting on peripheral targets via neurovascular pathways. Its effects on smooth muscle preparations indicate it can stimulate contraction in some tissues and relax in others. The peptide's physiological function remains unclear, but its presence in the hypothalamus suggests a potential role in neural signaling or modulation of nervous activity. Neurotensin's unique properties, including its hypotensive effects and acute tachyphylaxis, distinguish it from other known peptides. Its role in vascular regulation and inflammatory responses is also under investigation.