Human normal dermal fibroblasts express somatostatin receptors

The hormone/neuropeptide somatostatin (SOM) exerts multiple functions in the central nervous system, the immune system, the hypothalamo-pituitary axis, the gastrointestinal tract, and the pancreas. Endogenous SOM occurs in 2 biologically active forms, with 14 or 28 amino acids. Five subtypes of SOM receptors have been cloned. SOM is present in human skin. We have investigated the expression of SOM receptors on human dermal normal fibroblasts. Biotinyl-SOM allowed the visualization of SOM receptors on human dermal fibroblasts. Radioligand binding studies with (3-[125I]iodotyrosyl11)-SOM-14 were performed on these cells and the effect of SOM-14 on the DNA synthesis by fibroblasts was evaluated by measuring [3H]-methyl thymidine incorporation. Saturation curve, and Scatchard plot showed a homogeneous class of receptors with a Bmax of 0.055 +/- 0.023 nM and KD of 2.0 +/- 0.4 nM (values: mean +/- SEM). Fibroblasts expressed 3,317 +/- 1,385 binding sites per cell. Competitive displacement experiments showed that SOM-14 IC50 was 69.3 +/- 4.5 nM (mean +/- SEM), for SOM-28 33.2 +/- 6.0 nM and for octreotide 36.5 +/- 3.3 nM. The KI values calculated from these IC50 were, respectively: 62.4 +/- 4.1 nM; 29.9 +/- 5.4 nM; 32.9 +/- 2.9 nM. We conclude that subtype 2 or 3 SOM receptors is present on human normal dermal fibroblasts. A weak effect of SOM-14 on DNA synthesis was observed with SOM concentrations of 10(-7) and 10(-6) M.