Activity profiles of dalargin and its analogues in mu-, delta- and kappa-opioid receptor selective bioassays.
1. To elucidate the structural features ensuring action of [D-Ala2, Leu5]-enkephalyl-Arg (dalargin), a series of dalargin analogues were tested for their effectiveness in depressing electrically-evoked contractions of the guinea-pig myenteric plexus-longitudinal muscle preparations (mu- and kappa-opioid receptors) and the vasa deferentia of the hamster (delta-opioid receptors), mouse (mu-, delta- and kappa-opioid receptors), rat (similar to mu-opioid receptors) and rabbit (kappa-opioid receptors). The naloxone KB values in the myenteric plexus were also obtained. 2. [L-Ala2]-dalargin was 19 times less potent than dalargin, and its pharmacological activity was peptidase-sensitive. The ratio of delta-activity to mu-activity for [L-Ala2]-dalargin was 6.78, and KB was 7.9 nM. This emphasizes the role that D-configuration of Ala2 plays in determining the active folding of dalargin molecule as well as in conferring resistance to peptidases. 3. [Met5]-dalargin was equipotent to dalargin in the myenteric plexus, but was more potent in the vasa deferentia of hamster and mouse (KB=5.5 nM). Leu5 and the interdependence of Leu5 and D-Ala2 are of importance for the selectivity of dalargin for mu-opioid receptors. 4. Dalarginamide was more potent and selective for mu-opioid receptors than dalargin, whilst dalarginethylamide, though equipotent to dalarginamide in the myenteric plexus, was more potent at delta-opioid receptors (KB=5.0 nM). [D-Phe4]-dalarginamide and N-Me-[D-Phe4]-dalarginamide were inactive indicating the contribution of L-configuration of Phe4 to the pharmacological potency of dalargin. 5. N-Me-[L-Phe4]-dalarginamide possessed the highest potency and selectivity for mu-opioid receptors (the ratio of delta-activity to mu-activity was 0.00053; KB=2.6 nM). The CONH2 terminus combined with the N-methylation of L-Phe4 increased the potency and selectivity of dalargin for mu-opioid receptors.
Pencheva
N
N
Institute of Physiology, Bulgarian Academy of Sciences, Acad. G. Bonchev Street, Block 23, 1113 Sofia, Bulgaria. nevena@iph.bio.bas.bg
Pospisek
J
J
Hauzerova
L
L
Barth
T
T
Milanov
P
P
D000595:Amino Acid Sequence; D000818:Animals; D001681:Biological Assay; D006224:Cricetinae; D016308:Enkephalin, Leucine-2-Alanine / Q000031:analogs & derivatives* / Q000737:chemistry / Q000494:pharmacology; D006168:Guinea Pigs; D066298:In Vitro Techniques; D008297:Male; D008647:Mesocricetus; D051379:Mice; D009197:Myenteric Plexus / Q000187:drug effects; D009270:Naloxone / Q000494:pharmacology; D009292:Narcotic Antagonists / Q000494:pharmacology; D011817:Rabbits; D051381:Rats; D017208:Rats, Wistar; D011957:Receptors, Opioid / Q000187:drug effects*; D014649:Vas Deferens / Q000187:drug effects
D009292:Narcotic Antagonists; D011957:Receptors, Opioid; D009270:Naloxone; D016308:Enkephalin, Leucine-2-Alanine; C040996:enkephalin-Leu, Ala(2)-Arg(6)-