Do human platelets have opiate receptors?

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Abstract
In their study of prostaglandin E1 (PGE1)-sensitive adenylate cyclase (AC) in rat brain homogenates, Collier and Roy1 claimed that the activity of this enzyme is inhibited by opiates. They also proposed that opiates exert their analgesic and allied effects by inhibiting AC of neurones that are normally stimulated by E prostaglandins2. Studies using neuroblastoma × glioma hybrid cells3,4 supported this hypothesis. However, subsequent studies with the mammalian brain5,6 and rat brain tissue slices7,8 yielded conflicting results. PGE1, also inhibits platelet aggregation9, probably through activation of platelet AC10. Gryglewski et al.11 showed that morphine inhibits the anti-aggregating effect of PGE1 on ADP- and adrenaline-induced platelet aggregation, and suggested that the inhibition by morphine is mediated through platelet AC activity. We report here our attempts to reproduce the results of Gryglewski et al. and our examination of the effect of morphine on PGE1-sensitive AC activity in platelet lysates and on PGE1-induced accumulation of cyclic AMP in intact platelets. The possible existence of opiate receptors in platelets was also assesed by direct binding studies with 3H-etorphine. In contrast to Gryglewski et al.11, we could not detect any effect of opiates on the aggregation of human platelets, nor did we find any other evidence supporting the presence of opiate receptors in these cells. Thus we conclude that the presence of opiate receptors in human platelets is unlikely.