No Role for Phospholipase A2and Protein Kinase C in the Potentiation by ?-Adrenoceptors of ?-Adrenoceptor-Mediated Cyclic AMP Formation in Rat Brain

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Abstract
This study ws undertaken to examine the role of phospholipase A2 and protein kinase C in the potentiation of .beta.-adrenoceptor-mediated cyclic AMP formation by .alpha.-adrenceptors in rat cerebral cortical slices. Inhibition of arachidonic acid metabolism by a range of cyclooxygenase and lipoxygenase inhibitors had no effect on the potentiation of isoprenaline-stimulated cyclic AMP. Conversely, stimulation of leukotriene formation had no effect on the response to isoprenaline. The phospholipase A2 activator, melittin, stimulated cyclic AMP and potentiated the effect of isoprenaline, but these responses were not influenced by cyclooxygenase or lipoxygenase inhibitors. Indomethacin was also ineffective against the potentiation of vasoactive intestinal peptide-stimulated cyclic AMP by noradrenaline. Phorbol ester potentiated the cyclic AMP response to isoprenaline, and this potentiation was antagonized by three different putative protein kinase C inhibitors. However, the same inhibitors did not affect the .alpha.-adrenoceptor-stimulated enhancement of the response to isoprenaline. We have found no evidence, therefore, to support the suggestion that arachidonic acid and its metabolites and/or potein kinase C mediate the .alpha.-adrenoceptor modulation of .beta.-adrenoceptor function.

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