Somatostatin: A Hormone for the Heart?

Somatostatin (somatotropin release inhibitory factor; SRIF) peptides are widely distributed throughout the mammalian body and act through a family of genetically distinct, guanine nucleotide regulatory protein coupled (Gprotein- coupled), cell surface receptors (sst1-5). Compelling evidence shows that SRIF and SRIF peptidyl analogs modulate vascular function, with actions upon smooth muscle and endothelium. SRIF receptors are known to exist in the carotid endothelium, a principal target for the pro-inflammatory cascade that accompanies coronary artery disease. SRIF- 14 and SRIF analogs are anti-inflammatory but the molecular mechanism involved remains unclear. Since crucial steps in the endothelial inflammation response include endothelial activation by cytokines, adhesion molecule expression and cellmonocyte interactions, peptide agents that inhibit these steps might provide a novel strategy for reducing vascular inflammation. SRIF, acting through its cognate receptors, modulates a variety of intracellular effectors that are linked to inflammation including phosphotyrosine phosphatases, the extracellular regulated protein kinase 1 and 2 (ERK1/2) cascade, adenylyl cyclase and endothelial nitric oxide synthase. Directly or indirectly, SRIF also functions to inhibit endothelial cell proliferation and induce apoptosis. A detailed understanding of SRIF actions could provide a rational basis for using SRIF ligands in controlling vascular inflammation and inhibiting cytokine signaling, critical events in atherogenesis.