Somatostatin at nanomolar concentration reduces collagen I and III synthesis by, but not proliferation of activated rat hepatic stellate cells

1 Previous studies have shown antifibrotic effects of somatostatin. Since hepatic stellate cells (HSC) express somatostatin receptors and play a key role in hepatic fibrogenesis, we investigated the in vitro antifibrotic effect of somatostatin on rat HSC. 2 At day 12 after isolation, cells were exposed to different concentrations of somatostatin (10(-6)-10(-9) mol l(-1)). 3 mRNA expression of collagen types I and III, and of smooth muscle alpha-actin (alpha-SMA) was analysed by Northern blotting. At 10(-9) mol l(-1), somatostatin significantly reduced mRNA expression of collagen I ( 72.3 +/- 10.7%; 95% confidence interval (95% CI): 45.5-99.0), collagen III (79.0 +/- 4.5%; 95% CI: 67.6-90.4) and alpha-SMA (65.7 +/- 5.9%; 95% CI: 51.1-80.2), as compared to control normalized at 100%. These results were confirmed by quantitative RT-PCR. 4 Cycloheximide experiments indicated that somatostatin has no direct transcriptional effect. 5 Using immunoprecipitation, we demonstrated that somatostatin also decreased de novo synthesis of collagen I (73 +/- 10%; 95% CI: 48-98%), collagen III (65 +/- 13%; 95% CI: 33-97%) and alpha-SMA (47 +/- 9%; 95% CI: 25-69%). Remarkably, at higher concentrations, somatostatin did not suppress collagen mRNA expression nor de novo protein synthesis. We ascribe this observation to desensitization of the cells for somatostatin. 6 Cell proliferation, as measured by 5-bromo-2'-deoxyuridine labelling, was not altered by somatostatin. 7 No significant effect on the intermediate and actin cytoskeleton were detected by immunohistochemistry and Western blotting. 8 Our findings imply that in vivo antifibrotic effects of somatostatin could result partially from a direct action of somatostatin on HSC, but other, in vivo effects are probably also involved.