EFFECT OF SOMATOSTATIN ON THE MASS ACCUMULATION OF INOSITOL-1,4,5-TRISPHOSPHATE IN RAT HYPOTHALAMUS, STRIATUM, FRONTOPARIETAL CORTEX AND HIPPOCAMPUS

Somatostatin-14 (SS) significantly increased inositol-1,4,5-trisphosph ate (IP3) accumulation in rat hypothalamic, striatal, frontoparietal c ortical and hippocampal slices. However, this stimulation of IP3 accum ulation by SS was highest in the frontoparietal cortex and hippocampus . The effect was already significant with 0.01 mu M in the frontoparie tal cortex (P<0.05) and hippocampus (P<0.05) and the maximal accumulat ion was evident with 0.1 mu M SS, in all areas studied. A concentratio n of 1 mu M SS, lacked this effect in hypothalamus and striatum. SS ra pidly increased IP3 accumulation in all brain areas studied. This effe ct was maximal at 15 s of incubation and decreased subsequently. At 60 s incubation, levels were still elevated in frontoparietal cortex and hippocampus but had returned to basal values in hypothalamus and stri atum. Somatostatin-28 (SS-28) and the SS analogues, D-Trp(8)-D-Cys(14) and SMS 201-995, also significantly stimulated IP3 accumulation altho ugh the effect of SMS 201-995 was greater than that of SS in the stria tum in comparison with controls (P<0.001 and P<0.01, respectively). Th ese results suggest that SS action at the hypothalamus, striatum, fron toparietal cortex and hippocampus is mediated at least in part by the accumulation of IP3, which may initiate intracellular processes respon sible for some biological SS effects.