Differential effects of somatostatin on adenylate cyclase as functional correlate for different brain somatostatin receptor subpopulations.

In homogenates of rat hippocampus and striatum, but not substantia nigra, somatostatin (SRIF) inhibits forskolin-activated adenylate cyclase in nanomolar concentrations. However, SRIF can also stimulate adenylate cyclase in micromolar concentrations in homogenates of rat hippocampus and substantia nigra. The SRIF octapeptide SMS 201-995 solely inhibits the forskolin-activated adenylate cyclase in the 3 preparations. These results suggest that the SRIF-specific stimulation of adenylate cyclase may be a functional correlate for the brain-specific SRIF receptor subpopulation, whereas the SRIF and SMS 201-995 inhibition of stimulated adenylate cyclase correlate with the SRIF receptor subpopulation present in brain and non-neuronal tissues.