Molecular pharmacology of somatostatin receptors

The neuropeptide somatostatin (SRIF) is widely expressed in the brain and in the periphery in two main forms, SRIF-14 and SRIF-28. Similarly, the presence of SRIF receptors throughout the whole body has been reported. SRIF produces a variety of effects including modulation of hormone release (e.g. GH, glucagon, insulin), of neurotransmitter release (e.g. acetylcholine, dopamine, 5-HT), and its own release is modulated by many neurotransmitters. SRIF affects cognitive and behavioural processes, the endocrine system, the gastrointestinal tract and the cardiovascular system and also has tumor growth inhibiting effects. Initially, two classes of SRIF receptors have been proposed on the basis of biochemical and functional studies. However, the recent cloning of five putative SRIF receptor subtypes which belong to the G-protein coupled receptor superfamily suggests that SRIF mediates its various effects via a whole family of receptors. Here we review, in this new context, the molecular pharmacology of the SRIF receptor subtypes present in the brain and in the periphery, and address the question of nomenclature of SRIF receptors.