Stimulation by noradrenaline of inositol phospholipid breakdown in the rat hippocampus: effect of the ambient potassium concentration

The stimulation by noradrenaline (NA) of inositol phospholipid (PI) breakdown has been studied using rat hippocampal miniprisms. Pretreatment with the monoamine oxidase inhibitor, pargyline, potentiated the stimulation produced by NA. On the other hand, pargyline pretreatment did not affect the stimulation of PI breakdown by the alpha 1-adrenoceptor agonist phenylephrine. NA- and phenylephrine-stimulated PI breakdown were enhanced by increasing the ambient potassium concentration in the assay from 5.88 to 18.2 mM. This enhancement did not, in the case of NA, change either the EC50 value for this agonist (2-3 microM) or the pA2 value for the competitive antagonism of the stimulation by the alpha 1-antagonist prazosin (pA2 value 9.2). Time-courses of the NA-stimulated PI turnover in different brain regions indicated that the rate of stimulation was in the order frontal cortex greater than hypothalamus greater than or equal to hippocampus much greater than cerebellum.