An unconventional response of adenylate cyclase to morphine and naloxone in the chicken during early development.

The developmental profile of basal, NaF- and forskolin-stimulated adenylate cyclase [ATP-pyrophosphatelyase (cyclizing), EC 4.6.1.1] activity was established throughout the 21-day embryonic age of the chicken. The highest activities were observed from day 6 to day 8. Morphine inhibited NaF- and forskolin-stimulated brain adenylate cyclase activities only at days 6-8. The inhibition was not reversed by the antagonist naloxone, which also inhibited the enzyme during the same embryonic period and had no inhibitory effect thereafter. Thus, this action of morphine is not mediated through the conventional opiate receptor-adenylate cyclase system. We propose that the temporal specificity of this effect of morphine may play a role in the development of prenatal opiate effects.