ch-275 and seglitide

Somatostatin and its receptors (sst(1) and sst(2)) have been localized in brain nuclei implicated in motor control, such as the nucleus accumbens, ventral pallidum (VP) and substantia innominata (SI).. The objective of the study is to investigate the effect of somatostatin and selective sst(1) and sst(2) analogs infused in the VP/SI on the locomotor activity of the rat.. Somatostatin (15, 30, 60, 120 and 240 ng/0.5 microl/side), CH275 (sst(1) analog; 60, 180, 240 and 480 ng/0.5 microl/side), MK678 (sst(2) analog; 120, 240 and 480 ng/0.5 microl/side), L-809,087 (sst(4) agonist, 240 ng/0.5 microl/side) or saline (vehicle) were infused bilaterally in the VP/SI of the rat and locomotor activity measured for 60 min. The effect of SRA-880 (sst(1) antagonist) and CYN-154806 (sst(2) antagonist) on somatostatin-, CH275- and MK678-mediated locomotor activity was also ascertained.. Somatostatin decreased locomotor activity in the first 30 min after its infusion in the VP/SI and in a dose-dependent manner. The sst(1) and sst(2) antagonists, SRA-880 and CYN-154806, respectively, reversed the somatostatin effect. The sst(1) and sst(2) agonists CH275 and MK678, respectively, mimicked somatostatin's actions, while the selective sst(4) agonist L-809,087 had no effect. Moreover, SRA-880 and CYN-154806 reversed the respective agonist action on locomotor activity.. The present study provides functional evidence for the presence of sst(1) and sst(2) receptors in the VP/SI and their implication in motor control. The mechanism via which somatostatin and agonists mediate the attenuation of locomotor activity is presently being investigated.

Topics: Animals; Dose-Response Relationship, Drug; Globus Pallidus; Injections, Intraventricular; Male; Motor Activity; Oligopeptides; Peptides, Cyclic; Piperazines; Quinolines; Rats; Rats, Sprague-Dawley; Receptors, Somatostatin; Somatostatin; Stereotaxic Techniques; Substantia Innominata; Time Factors

The role of somatostatin and its mechanism of action in the retina remains an important target for investigation. Biochemical and pharmacological studies were engaged to characterize the somatostatin receptors in the rabbit retina, and their coupling to G-proteins. The ability of selective ligands to inhibit [125I]Tyr11-somatostatin-14 binding to rabbit retinal membranes was examined. The sst2 analogues SMS201-995, MK678, and BIM23014, displayed IC50 values of 0.28 +/- 0.12, 0.04 +/- 0.01 and 1.57 +/- 0.39 nm, respectively. The sst1 analogue CH275 moderately displaced the [125I]Tyr11-somatostatin-14 binding, while selective analogues for sst3, sst4 and sst5 had minimal effect. Immunoblotting and/or immunohistochemistry studies revealed the presence of the pertussis toxin sensitive Gi1/2, and Go proteins, as well as Gs. Somatostatin-14 and MK678 stimulated GTPase activity in a concentration-dependent manner with EC50 values of 42.8 +/- 16.8 and 70.0 +/- 16.5 nm, respectively, thus supporting the functional coupling between the receptor and the G-proteins. CH275 stimulated the GTPase activity moderately, in agreement with its binding profile. The antisera raised against Goalpha and Gi1/2alpha inhibited the somatostatin-induced high-affinity GTPase activity, but only anti-Goalpha inhibited the MK678 stimulation of the enzyme. These results suggest that somatostatin mediates its actions in the rabbit retina by interacting mainly with sst2 receptors that couple to Goalpha.

Topics: Animals; Binding, Competitive; Blotting, Western; Cell Membrane; Dose-Response Relationship, Drug; Enzyme Activation; GTP Phosphohydrolases; GTP-Binding Protein alpha Subunit, Gi2; GTP-Binding Protein alpha Subunits, Gi-Go; Heterotrimeric GTP-Binding Proteins; Immune Sera; Ligands; Male; Peptides, Cyclic; Proto-Oncogene Proteins; Rabbits; Radioligand Assay; Receptors, Somatostatin; Retina; Somatostatin

Somatostatin receptors (SSTRs) are known to mediate diverse cellular responses. Most target cell express more than one SSTR isoform, making it difficult to define the signalling pathway used by individual receptor subtypes. Thus, we have expressed SSTR1 or SSTR2 in rat pituitary F4C1 cells which lack endogenous SSTRs. Using a silicon-based biosensor system, the Cytosensor microphysiometer, which measures the extracellular acidification rate (ECAR) in real time, we have studied the responses to SS mediated by either SSTR1 or SSTR2. In control F4C1 cells, SS had no effect on the basal ECAR. In transfected cells expressing only SSTR1, SS caused a unique decrease in ECAR in a concentration-dependent manner. Receptor-mediated decreases in ECAR have not been reported previously. In F4C1 cells expressing only SSTR2, SS induced a bidirectional ECAR response, a rapid increase followed by a decrease below basal. Two SS analogues, MK678 and CH275, induced characteristic ECAR responses with the expected receptor selectivities for SSTR1 or SSTR2. Pretreatment of F4C1 cells with pertussis toxin abolished the decreases in ECAR mediated by both SSTR1 and SSTR2, but only partially reduced the increase in ECAR mediated by SSTR2. The decrease in ECAR did not depend on a decrease in intracellular cAMP. The ECAR responses to SS were modestly attenuated by methylisobutylamiloride (MIA), an inhibitor of the ubiquitous Na(+)-H+ exchanger NHE1. Removal of extracellular Na+ greatly inhibited the ECAR responses to SS, demonstrating a role for both amiloride-sensitive and -insensitive Na(+)-dependent acid transport mechanisms in SS-induced extracellular acidification. In conclusion, we have identified and characterized different signalling pathways for SSTR1 and SSTR2 in pituitary cells as measured by microphysiometry.

Topics: Animals; Cyclic AMP; GTP-Binding Proteins; Hormone Antagonists; Peptides, Cyclic; Pertussis Toxin; Rats; Receptors, Somatostatin; Signal Transduction; Sodium-Hydrogen Exchangers; Somatostatin; Tumor Cells, Cultured; Virulence Factors, Bordetella