Potencies of various neurotensin-(8-13) analogs for inhibition of heat-induced edema in the anesthetized rat

The neurotensin fragment AcNT(8-13) inhibits lowering of interstitial fluid pressure in rat trachea

Injury to soft tissue results in the lowering of interstitial fluid pressure (P(if)), plasma protein extravasation, and increased total tissue volume. In this study, the effects of N-acetyl neurotensin(8-13) [AcNT(8-13)] on P(if) in rat trachea were examined after electrical stimulation (ES) of the vagus nerve. P(if) was measured with glass capillaries connected to a servocontrolled counterpressure system. In pentobarbital-anesthetized female Wistar rats, the P(if) after intravenous saline was -1.8 +/- 0.3 mmHg (means +/- SD) and decreased to -5.0 +/- 0.6 mmHg (P < 0.01, n = 9) after ES. AcNT(8-13) (10 microg/kg) blocked the fall in P(if) after ES (-2.5 +/- 2.3 mmHg, P < 0.01, n = 8). In tracheal tissue from animals pretreated with AcNT(8-13) at the same dose and immersed in phosphate-buffered saline (0.15 M, pH 7.4), the rate of fluid accumulation in excised tissues was significantly reduced after 2 h. The ability of AcNT(8-13) to modulate the fluid mechanics of tracheal interstitium after inflammation suggests that it may be a useful tool for studying cell adhesion and related factors that maintain structural integrity of connective tissue after injury.

Lowering of interstitial fluid pressure after neurogenic inflammation is inhibited by mystixin-7 peptide

Soft tissue injury is accompanied by lowering of interstitial fluid pressure (P(if)), plasma protein extravasation, and edema. Inflammation was produced by electrical stimulation (ES) of the vagus and the effects of the synthetic peptide mystixin-7 (p-anisoyl-Arg-Lys-Leu-Leu-D-Thi-Ile-D-Leu-NH(2)) on P(if) were examined. Micropuncture measurement of P(if) in submucosa, without opening the trachea, was conducted on rats anesthetized with pentobarbital sodium (50 mg/kg) and euthanized with intravenous KCl. P(if) in control (intravenous saline) was -1.2 +/- 0.7 mmHg before ES and decreased to -4.7 +/- 1.0 mmHg (P < 0.01, n = 8) after ES. Mystixin-7 (10 and 20 microg/kg iv) blocked the fall in P(if) after ES (-1.1 +/- 0.3 and -0.8 +/- 0.2 mmHg, P < 0.01, n = 8 and n = 4). The 1 microg/kg dose was without effect. When trachea from animals pretreated with mystixin-7 (20 microg/kg iv) were soaked in phosphate-buffered saline (0.15 M, pH 7.4), the rate of fluid accumulation was significantly reduced. This study suggests that mystixin peptides, which have structural similarity to a fragment from laminin-alpha1 chain, may be useful tools for studying cell adhesion and factors that maintain the structural integrity of connective tissue after injury.

Stimulation of cell-surface urokinase-type plasminogen activator activity and cell migration in vascular endothelial cells by a novel hexapeptide analogue of neurotensin

To investigate if neurotensin (NT) could induce activation of urokinase-type plasminogen activator (uPA) in vascular endothelial cells, we utilized the acetyl-NT (8-13) analogue, TJN-950, in which the C-terminal leucine is reduced to leucinol. TJN-950 inhibited the binding of 125I-NT to membranes of newborn rat brains and of COS-7 cells transfected with rat NT receptor cDNA, but at 10(4) higher doses than NT (8-13). However, TJN-950 was as effective as NT in inducing the fibrinolytic activity in bovine vascular aortic and human umbilical vein endothelial cells, and enhanced the migration of vascular endothelial cells. Moreover, administration of TJN-950 induced neovascularization in the rat cornea in vivo. TJN-950 had no effect on expression of uPA, plasminogen activator inhibitor-1 or uPA receptor mRNA. The binding of 125I-TJN-950 to cell membranes was blocked by unlabeled uPA and TJN-950, but not the amino-terminal or 12-32 fragment of uPA. TJN-950 may enhance uPA activity in vascular endothelial cells by interacting with the uPA receptor, resulting in induction of angiogenesis.

Neurotensin induces the release of prostacyclin from human umbilical vein endothelial cells in vitro and increases plasma prostacyclin levels in the rat

Human umbilical vein endothelial cells express high affinity neurotensin receptors which are coupled to phosphoinositide turnover and 45Ca2+ efflux (Schaeffer et al., 1995. J. Biol. Chem. 270, 3409-3413). In order to assess the physiological significance of neurotensin receptor activation in endothelial cells, we have compared the in vitro effect of neurotensin on prostacyclin release and cytosolic free calcium increase ([Ca2+]i) as determined by fura-2 fluorescence experiments to the in vivo effect of neurotensin on blood pressure and haematocrit. Neurotensin increased [Ca2+]i levels at low concentrations (EC50 = 4.2 +/- 0.2 nM, n = 3). At similar concentrations, neurotensin was also able to induce prostacyclin release from human umbilical vein endothelial cells (EC50 = 14 +/- 1 nM, n = 3) as determined by a 6-keto-prostaglandin F1 alpha enzyme immunoassay. The neurotensin (100 nM)-induced [Ca2+]i increase and prostacyclin release were inhibited by the specific non-peptide neurotensin receptor antagonist SR 48692 at similar concentrations (IC50 = 41 +/- 16 nM and 86 +/- 17 nM, respectively, n = 3), confirming that these responses were mediated by high affinity neurotensin receptors. Intravenous injection of neurotensin (1-4 nmol/kg i.v.) in the rat resulted in a drop of blood pressure and increased haematocrit, and nearly doubled the plasma levels of 6-keto-prostaglandin F1 alpha, the stable metabolite of prostacyclin. Whereas indomethacin (10 mg/kg i.v.) pretreatment significantly reduced the effect of neurotensin on blood pressure, it did not alter its effect on haematocrit. These results suggest that prostacyclin release plays a role in the hypotensive effects of neurotensin, but is not involved in its effects on haematocrit.