Somatostatin (SRIF) is a neurotransmitter in the brain involved in the regulation of motor activity and cognition. It induces its physiological actions by interacting with receptors. We have developed antibodies against the receptor to investigate its structural properties. Rabbit polyclonal antibodies were generated against the rat brain SRIEF receptor. These antibodies (F4) were able to immunopeipitate solubilized SRIF receptors from rat brain and the cell line . The specificity of the interaction of these antibodies with SRIF receptors was further demonstrated by immunoblotting. F4 detected SRIF receptors of 60 kDa from rat brain and adrenal cortex and the cell lines AtT-20, GH3, and NG-108, which express high densities of SRIEF receptors. They did not detect immunoreactive material from rat liver or COS-l, HEPG, or CRL cells, which do not express functional SRIF receptors. In rat brain, 60-kDa immunoreactivity was detected by F4 in the hippocampus, cerebral cortex, and striatum, which have high densities of SRIF receptors. However, F4 did not interact with proteins from cerebellum and brain stem, which express few SRIF receptors. Immunoreactive material cannot be detected in rat pancreas or pituitary, which have been reported to express a 90-kDa SRIF receptor subtype. The selective detection of 60-kDa SRIF receptors by F4 indicates that the 60-and 90-kDa SRIF receptor subtypes are immunologically distinct. The availability of antibodies that selectively detect native and denatured brain SRIF receptors provides us with a feasible approach to clone the brain SRIF receptor gene(s).Somatostatin (SRIF) is a neuropeptide, which was originally isolated from hypothalamus and shown to be the major physiological inhibitor of growth hormone secretion from the pituitary (1). It is also expressed in delta cells of the pancreatic islets, where it regulates the balance between insulin and glucagon release, and in mucosal cells of the stomach, where it has been reported to modulate gastric acid secretion (2). This peptide is also synthesized in discrete neuronal populations in brain, where it has a role in modulating motor activity and cognitive processes (3,4).SRIF induces its biological activity by interacting with membrane-bound receptors. The properties of SRIF receptors have been analyzed by using a variety of biochemical approaches. To characterize the physical properties of the receptor, techniques were developed to covalently crosslink the receptor with radioactive SRIF analogs and to analyze the tagged receptor by gel electrophoresis and autoradiography. The results of these studies have shown that heterogeneities exist in the structure of SRIF receptors. SRIF receptors from pancreatic acinar cells (5), pituitary cells (6), and GH4C1 cells (7) were reported to migrate as a mass of90 kDa in denaturing gels. In contrast, SRIF receptors from rat brain (8, 9), adrenal cortex (10), and the cell lines AtT-20 and GH3 (11) are 60 kDa in size. The diversity of size of SRIF receptor subtypes may be due to variations ...
