Somatostatin receptor gene expression and inhibitory effects of octreotideon primary cultures of orbital fibroblasts from Graves' ophthalmopathy

To explore the mechanism underlying the effects of the somatostatin (SST) a nalogue octreotide in Graves' ophthalmopathy (GO), we investigated the expr ession of SST and of SST receptor (sst(1-5)) genes in primary cultures of f ibroblasts established from retroorbital tissue of GO patients and of contr ol subjects. We determined also SST specific binding sites by competitive b inding of [I-125-Tyr(11)]SST-14 and the effect of octreotide on cell growth , cAMP accumulation, Bcl-2 intracellular levels and apoptosis in GO fibrobl ast primary cultures. All primary cultures expressed the SST gene transcrip t and one or more ssts that have a high affinity for the two analogues (cla ss 1 sst). The sst(2) transcript was found in nine, sst(3) in five and sst( 5) in eight out of ten GO cell cultures. Sst(2) was detected in all six, an d sst(3) in four out of the six control cell cultures. Sst(4) was absent fr om all samples, and sst(1) was found only in six out of the ten GO samples. SST-14 and octreotide inhibited the binding of [I-125-Tyr(11)]SST-14 with a half-maximal inhibition of binding (IC50) of 0.80+/-0.37 and 33.7+/-33.1 nmol/l respectively in GO cell cultures, and with an IC50 of 0.9 and 1.5 nm ol/l in control cultures. Octreotide (10(-6) and 10(-7) M) significantly de creased (P<0.001) forskolin-induced but not basal cAMP accumulation; at bot h doses for 72 h it inhibited cell growth (20 and 55% respectively), and in duced apoptosis (20 and 40%), and abolished Bcl-2 protein in cell lysates. In conclusion, SST and sst transcripts are expressed and functional in cult ured retroorbital fibroblasts. The presence of class 1 sst in GO tissue and the inhibition exerted by octreotide on retroorbital cell growth and activ ity in vitro may account for the effects of SST analogue administration in vivo in GO.