enkephalin--ala(2)-mephe(4)-gly(5)- and 4-methoxymethylfentanyl

SH-SY5Y (human neuroblastoma) cultured cells, known to have mu-opioid receptors, have been used to assess and compare the ability of eight representative mu-selective compounds from diverse opioid families to recognize and activate these receptors. A wide range of receptor affinities spanning a factor of 10,000 was found between the highest affinity fentanyl analogs (Ki = 0.1nM) and the lowest affinity analog, meperidine (Ki = 1 microM). A similar range was found for inhibition of PGE1-stimulated cAMP accumulation with a rank order of activities that closely paralleled binding affinities. Maximum inhibition of cAMP accumulation by each compound was about 80%. Maximum stimulation of GTPase activity (approximately 50%) was also similar for all compounds except the lowest affinity meperidine. Both effects were naloxone reversible. These results provide further evidence that mu-receptors are coupled to inhibition of adenylate cyclase and that the SH-SY5Y cell line is a good system for assessment of mu-agonists functional responses.

Topics: Alprostadil; Analgesics; Cyclic AMP; Endorphins; Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; Enkephalins; Fentanyl; GTP Phosphohydrolases; Humans; Meperidine; Morphinans; Naloxone; Narcotics; Oxymorphone; Receptors, Opioid; Receptors, Opioid, mu; Tumor Cells, Cultured

Receptor binding assays using [3H]DAGO ([D-Ala2,MePhe4-Gly5-ol]enkephalin) (mu), [3H]DPDPE ([D-Pen2,D-Pen5]enkephalin) (delta) and [3H]U-69593 (kappa) were done in guinea pig whole brain membranes. Agonist activity was determined in norbinaltorphimine or beta-funaltrexamine (beta-FNA) treated guinea pig ileum (mu and kappa, respectively) and beta-FNA-treated mouse vas deferens (delta). The compounds with highest affinity were the most potent at the mu-receptor. The selectivity observed in the binding affinities was also found in in vitro activity. No correlation was found between mu-affinity and selectivity; the highest affinity analog, lofentanil, was found to be among the least selective, while another high affinity analog, R30490, was the most mu-selective. The results show that not all fentanyls are highly mu-selective, and could produce actions through delta- and kappa-opiate receptors.

Topics: Analgesics, Opioid; Animals; Benzeneacetamides; Brain; Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; Enkephalin, D-Penicillamine (2,5)-; Enkephalins; Fentanyl; Guinea Pigs; Ileum; Male; Mice; Naltrexone; Pyrrolidines; Receptors, Opioid; Receptors, Opioid, delta; Receptors, Opioid, kappa; Receptors, Opioid, mu; Vas Deferens