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Combined ETA/ETB receptor blockade of human peritoneal mesothelial cells inhibits collagen I RNA synthesis.

BACKGROUND
Peritoneal fibrosis is a serious complication of peritoneal dialysis; however, the mechanisms are poorly understood. We studied osmolarity and physical stress-induced effects on collagen I RNA synthesis in human peritoneal mesothelial cells (HPMCs) and focused on endothelin as a possible mediator.


METHODS
HPMCs were grown in a medium containing either d-glucose or glycerol to analyze the impact of osmolarity on mesothelial endothelin-1 (ET-1) release and on collagen I RNA synthesis [reverse transcription-polymerase chain reaction (RT-PCR)]. A cellular model of nonlaminar fluid shear stress and cellular stretch was used to analyze the effects of physical forces. To neutralize the endothelin effects, a combined ETA/ETB receptor antagonist (LU 302 872) was chosen.


RESULTS
Glucose, but not glycerol, increased mesothelial ET-1 release in a concentration and time-dependent manner (P < 0.05 vs. controls). Collagen I RNA synthesis was significantly higher in glucose-challenged cell cultures (P < 0.05 vs. controls). The glucose-mediated collagen I RNA synthesis was completely inhibited by adding the combined ETA/ETB receptor antagonist to the medium. Fluid shear stress, but not cellular stretch, led to a significant increase in the mesothelial ET-1 release (P < 0.005 vs. controls) and collagen I RNA synthesis (P < 0.05 vs. controls). LU 302 872 completely inhibited these effects.


CONCLUSION
We found that glucose and fluid shear stress are potent stimuli for ET-1 release and collagen I RNA synthesis in a model cellular system. Although our system is highly artificial, our findings raise the hypothesis that similar effects may occur in the peritoneal membranes of peritoneal dialysis patients and suggest that endothelin might be involved.