Somatostatin sst(5) inhibition of receptor mediated regeneration of rat aortic vascular smooth muscle cells

1 The aim of the present study was to determine the effect of somatostatin (SRIF) on mitogen-induced regeneration of rat aortic vascular smooth muscle cells (VSMC) and for comparison Chinese hamster ovary (CHO)-K1 cells expressing human recombinant sst(5) receptors (CHOsst(5)), following partial denudation of a confluent cell monolayer. Regeneration was assessd by measuring areas of recovery into the denuded area and by counting total cell numbers. 2 In VSMC, SRIF (0.1 nM-1 mu M) had no effect on the basal levels of regeneration but caused a concentration-dependent inhibition (pIC(50) 8.0-8.6) of the stimulated regeneration induced by sub-maximal concentrations of basic fibroblast growth factor (bFGF, 10 ng ml(-1)), platelet-derived growth factor-BB (PDGF, 5 ng ml(-1)) or endothelin-1 (ET-1, 100 nM). SRIF (pIC(50) 8.8) also inhibited bFGF-induced regeneration of CHOsst(5) cells. 3 In VSMC, the inhibitory action of SRIF on the regeneration induced by bFGF (10 ng ml(-1)) was due to an anti-proliferative effect, rather than an effect on cell migration, as SRIF (0.1 nM-1 mu M) abolished bFGF-induced increases in total cell numbers. The bFGF-induced increase in cell numbers was also abolished by actinomycin D (0.1 mu g ml(-1)). 4 The sst(5) receptor-selective agonist, L-362,855 (pIC(50) 10.5), was about 100 times more potent than SRIF at inhibiting bFGF-induced regeneration of both VSMC and CHOsst(5) cells whilst the sst(2) receptor-selective agonist, BIM-23027 (pIC(50) 6.8), was approximately 20 times weaker than SRIF. 5 The sst(5) receptor antagonist, BIM-23056 (100 nM), antagonized SRIF-induced inhibition of bFGF-induced regeneration in both VSMC and CHOsst(5) cells (estimated pK(B) values 8.8 and 8.3, respectively). 6 SRIF-induced inhibition of bFGF-induced regeneration of VSMC and CHOsst(5) cells was abolished by pretreating cells with pertussis toxin (100 ng ml(-1)) for 20 h. 7 These findings suggest that SRIF-induced inhibition of the proliferation of rat aortic VSMC is mediated via activation of receptors which are similar to human sst5 receptors. Furthermore this inhibitory effect is transduced via pertussis toxin-sensitive G(i)/G(o) proteins.