Luteinizing hormone-releasing hormone (LHRH) attenuates morphine-induced inhibition of cyclic AMP (cAMP) in opioid-responsive SK-N-SH cells

Abstract

SK-N-SH cells were used to assess the effects of luteinizing hormone-releasing hormone (LHRH) on opioid receptor-mediated changes in cyclic AMP (cAMP). Prostaglandin E 1 (PGE 1, 1 μM) caused a dramatic increase in cAMP levels. Treatment with 10 μM morphine (MOR) significantly inhibited the stimulatory effect of PGE 1. LHRH (0.8 μM) caused an increase in the basal level of intracellular cAMP and potentiated the stimulatory effect of PGE 1 on cAMP accumulation. In cells pretreated with LHRH the inhibitory effect of MOR on cAMP accumulation was significantly attenuated. An LHRH antagonist had no effect on cAMP. The involvement of pertussis toxin (PTX)-sensitive G proteins in the actions of LHRH was studied. PTX increased the stimulatory effect of PGE 1 on cAMP and attenuated the inhibitory effect of MOR. However, PTX pretreatment prevented the effects of LHRH on the intracellular actions of PGE 1 but exerted an additive effect with LHRH in blocking the MOR-induced decrease in cAMP levels. We conclude that LHRH attenuates the inhibitory, opioid receptor-mediated effect of MOR on intracellular cAMP accumulation in SK-N-SH cells, and that the G protein-independent mechanism may be involved in LHRH-induced attenuation of the inhibitory effect of MOR on neuronal cAMP.