Vapreotide is a somatostatin peptide analogue, which is commonly used for the treatment of oesophageal varicose veins in liver diseases. We study the effect of different concentrations of vapreotide on the ATPase activity of the cerebral and cerebellar membranes. Vapreotide 10-6 M produced the inhibition of Ca2+-ATPase activity, but not of other enzyme activities, suggesting a selective response according to the brain area and the preparation used as an enzyme source. Vapreotide at 10-9 to 10-6 M concentrations produced an inhibitory effect on Na+, K+-ATPase, resulting in an inhibitory concentration 50 (IC50) equal to 5.7 × 10-9 M and no changes in Mg2+-ATPase activity. Commercial enzymatic preparation of the pig cerebral cortex used as an enzyme source also produced an inhibitory enzyme effect. The vapreotide inhibitory effect was abolished by the addition of cSSTA, a somatostatin receptor antagonist. Besides, in crude membranes of cerebral cortex vapreotide produced [3H]-ouabain binding inhibition by direct interaction with the ouabain site (close to K+ site) in the enzyme Na+, K+-ATPase. The previous administration of the NOS inhibitor, Nω-nitro-L-arginine methyl ester (L-NAME), increased [3H]-ouabain binding. In this experimental condition, vapreotide could not displace many ouabain molecules bound with high affinity to its site. All these experiments provided evidence that ATPase could be one of the target sites for the effects of vapreotide at the neuronal level.
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