CAMP DECREASES STEADY-STATE LEVELS OF DELTA-OPIOID RECEPTOR MESSENGER-RNA IN NG108-15 CELLS

WE have compared several drug combinations for their ability to increa se basal cAMP and to down-regulate delta-opioid receptor mRNA levels. Continuous treatment for up to 48 h with a phosphodiesterase inhibitor in combination with the adenylyl cyclase activator forskolin showed a n early peak response, but cAMP levels returned to control after 8 and 24 h. Increases in cAMP level up to 150-fold were observed after trea tment for Ih with a series of drugs (rolipram, IBMX/forskolin, rolipra m/forskolin, dibutyryl cAMP, and prostaglandin E-2) that increase cAMP by different mechanisms. A significant decrease in DOR mRNA level, to 31% of control, followed the three treatments chat produced the large st increases in cAMP level: IBMX/forskolin, rolipram/forskolin, and pr ostaglandin E-2.