Endothelin is a dose-dependent trophic factor and a mitogen in small arteries in vivo.

Objective: Endothelin (ET) modulates cellular processes relevant to vascular remodeling, but there is still some debate as to the potential of ET to be a trophic factor or a mitogen. Moreover, the signaling of ET in vivo to produce these effects is largely unknown.

Methods: 3H-leucine and 3H-thymidine incorporation in rat small mesenteric arteries was studied with several doses of ET-1 (0.1-10 pmol/kg/min) administered for 26 h in vivo.

Results: The EC50 for protein synthesis was four times lower than that of DNA synthesis, with maximal effects around 1 and 3 pmol/kg/min, respectively. At 5 pmol/kg/min, ET enhanced CDK2 activity by reducing the binding of its inhibitor p27(Kip1). In contrast, the binding was enhanced at 0.5 pmol/kg/min. The reduced binding observed at 5 pmol/kg/min could not be explained by changes of p27(Kip1) or CDK2 content. Phosphorylation of p27(Kip1) on serine 10 was significantly reduced at 5 pmol/kg/min ET. Although the phosphoinositide 3-kinase pathway was activated, it did not contribute to the protein or DNA synthesis responses. Administration of 1 or 5 pmol/kg/min ET-1 for 28 days increased the thickness and cross-sectional area of the small mesenteric artery due to hypertrophy and hyperplasia, respectively, thus confirming the results obtained in acute conditions.

Conclusion: ET modulates p27(Kip1) binding to CDK2, producing hypertrophy at low and hyperplasia at higher concentrations. Taken together, these results suggest that ET can act both as a trophic factor and as a mitogen in an in vivo environment, depending on its local concentration.