Effects of opioid compounds on basal and muscarinic induced accumulation of inositol phosphates in cultured bovine chromaffin cells

The mammalian adrenal medulla expresses a variety of both opioid peptides and opioid receptors. The function of this adrenal opioid system is, however, largely unknown. We have examined the ability of a number of opioid compounds to influence basal and muscarinic stimulated accumulation of inositol phosphates in cultured bovine chromaffin cells. Muscarine produced a dose-dependent 1.5-fold increase in total inositol phosphates. This response was sensitive to atropine inhibition. The ten opioid compounds examined were chosen because between them they possess selectivity for all of the identified opioid receptor subtypes. However, none of these opioids in the concentration range 10nM-10 microM had any significant effect on either basal or muscarinic induced total inositol phosphate accumulation. We conclude that it is unlikely that opioid peptides released from either the chromaffin cells themselves or the splanchnic nerve can modulate the inositol phosphate second messenger system within the adrenal chromaffin cells.