Time-dependent Manner In Response Research Articles

Vascular Endothelial Growth Factor Increases Urokinase Receptor Expression in Vascular Endothelial Cells

Vascular endothelial growth factor (VEGF) is a potent angiogenic factor and endothelial cell-specific mitogen that stimulates urokinase-type plasminogen activator (uPA) activity in vascular endothelial cells. Here, we report that VEGF increases the high affinity binding of uPA to the same cells and that this binding is prevented by a peptide corresponding to the uPA receptor (uPAR) binding growth factor-like domain of uPA. Ligand cross-linking, ligand blotting, and uPA-Sepharose affinity chromatography revealed an increase in a cell surface uPA binding protein that corresponds to the uPAR on the basis of its affinity for uPA, M(r) of 50,000-55,000, and phosphatidylinositol-specific phospholipase C sensitivity. By Scatchard analysis, VEGF increased the number of uPAR molecules by 2.8-3.5-fold and concomitantly decreased their affinity for uPA. By northern blotting uPAR mRNA was increased in a dose- and time-dependent manner in response to VEGF. Taken together, these findings demonstrate that VEGF-induced angiogenesis is accompanied by increased uPAR expression and uPA activity on the endothelial cell surface. These observations are consistent with the notion that the uPA-uPAR interaction facilitates cellular invasion.

In vitro oral mucosa irritation testing with human cell cultures

Cell cultures are a potentially useful model to predict in vivo oral mucosa irritation. To this end, oral mucosa organ equivalent cultures (OMOEC) and skin equivalent cultures (SEC), both derived from human tissue, were evaluated for their responsiveness to test dentifrices with graded degrees of irritation potential. OMOEC and SEC were treated with test dentifrices and responses were evaluated by histopathology, cell viability (MTT incorporation), and cytotoxicity [release of aspartate aminotransferase (AST)]. Cell viability in OMOEC and SEC was reduced in a dose- and time-dependent manner in response to the test dentifrices. Correspondingly, AST release was increased in a dose- and time-dependent manner in response to the test dentifrices. These results demonstrate that OMOEC and SEC systems respond linearly to graded degrees of irritation potential as represented by generic dentifrices. Such results in an in vitro model of oral mucosa irritation allow direct comparison of in vitro responses with those obtained in an in vivo model, thus providing the groundwork for a tiered approach to assessment of irritation potential of oral care products.

Endothelin‐1 Stimulates Monocytes in vitro to ReleaseChemotactic Activity Identified as Interleukin‐8 and Monocyte Chemotactic Protein‐1

In the present study we examined whether endothelin-1 stimulation of human monocytes causes release of chemotactic factors. It was found that monocytes released neutrophil- and monocyte-chemotactic activity in a dose- and time-dependent manner in response to ET-1. ET-1 did not show any chemotactic activity by itself. NCA was detected in monocyte supernatants in response to ET-1 (0.01–100 nM) after 1, 4, 8 and 24 h stimulation. MCA was detected only after 24 h stimulation with ET-1 (0.1–100 nM). Preincubation of the monocyte cultures with the lipoxygenase inhibitors nordihydroguaiaretic acid (10−4 M) or diethylcarbamazine (10−9 M) completely abolished the appearance of NCA and MCA. NCA was neutralized by > 75% using a polyclonal antibody against human interleuktn-8. The ET-1 induced release of IL-8 was confirmed by IL-8 ELISA. A monoclonal antibody against human monocyte chemotactic protein-1 neutralized MCA by > 80%. It is concluded that ET-1 stimulation of monocytes in vitro causes release of neutrophil- and monocyte-chemotactic activity identified as IL-8 and MCP-I respectively. An intact lipoxygenase pathway is crucial for this effect of ET-1 to occur.

Proctolin and an Endogenous Proctolin-Like Peptide Enhance the Contractility of the Limulus Heart

ABSTRACT Synthetic proctolin increases the force but not the rate of heart contractions of Limulus in a time- and dose-dependent manner. The threshold of this effect is 3 X 10−10M and the EDS0 is approximately 10−10M. At concentrations up to 10−7 M, proctolin has no effect on the rhythmic electrical activity of the isolated cardiac ganglion, and it does not change the simple and compound postsynaptic potentials recorded at the cardiac neuromuscular junction. Proctolin acts directly on the cardiac muscle fibres. Electrically stimulated myocardia show a proctolin-induced increase in contraction amplitude with the same concentration dependence as the intact heart. A compound with an apparent molecular weight of 700–800 occurs in the Limulus nervous system, particularly in the cardiac ganglion. This compound resembles proctolin in being heat-stable, resistant to trypsin and chymotrypsin cleavage, and losing activity in a time-dependent manner in response to treatment with leucine aminopeptidase or pronase. This peptide induces spontaneous contractions and a contracture of the cockroach hindgut in a manner similar to proctolin. Moreover, the Limulus inotropic peptide, like proctolin, increases the force of contraction of the Limulus heart without affecting beat frequency. It is concluded that an endogenous, proctolin-like peptide is an inotropic modulator of the Limulus heart, acting directly on the muscle fibres and not affecting cardiac ganglion activity.