Varying expression of opioid receptors and GTP-binding proteins in human pheochromocytomas

The expression of opioid receptors and GTP-binding proteins was studied in 14 pheochromocytomas. The amounts of [3H]diprenorphine bound to membranes varied from 13 to 62 fmole/mg protein, but significantly higher in adrenaline-secreting tumors than in noradrenaline-secreting tumors. None of [3H]DADLE, [125I]beta-endorphin or [3H]ethylketocyclazocine binding was correlated with [3H]diprenorphine binding. Gpp(NH)p inhibition of [3H]DADLE binding was evident in all four normal human adrenal medullae but in only 8 out of 14 pheochromocytomas. The extent of Gpp(NH)p inhibition was not correlated with the amount of pertussis toxin (PT)-sensitive GTP-binding proteins as measured by PT-catalyzed [32P]ADP-ribosylation. The present findings suggest that opioid receptors and PT-sensitive GTP-binding proteins are variously expressed in transformed chromaffin cells, pheochromocytoma.