Add time:09/07/2019         Source:sciencedirect.com

Dynorphin A-(l-13)-Tyr14Leu15-Phe16-Asn17-Gly18-Pro19 (dynorphin Ia: a peptide derived from the structure of adrenal dynorphin I) was synthesized by the solid-phase procedure. The product was purified and compared with dynorphin A-(l–13) and [D-Pro10]dynorphin A-(1–11) for its ability to inhibit the electrically evoked contractions of the guinea pig ileum (GPI) and mouse vas deferons (MVD) and to compete with the binding of [3H]ethylketocyclazocine (κ ligand), [3H][D-Ala2]MePhe4,Glyol5]enkephalin (μ ligand) and [3H][D-Ser2Thr6]Leu-enkephalin (° ligand) to membrane preparations of the guinea pig cerebellum or rat brain. Additionally, the antinociceptive effects of the synthetic peptide were assessed in rat paw-pressure and tail-flick tests. In the GPI, dynorphin la possessed a relative potency (IC50 0.5 nM) that was comparable to that of [D-Pro10]dynorphin A-(1-11) (IC50 0.5 nM) or dynorphin A-(l–13) (IC50 0.7 nM). In the δ specific MVD assay, dynorphin la displayed a reduced potency (IC50 235 nM) as compared with that of dynorphin A-(l-13) (IC50 20 nM) or [D-Pro10]dynotphin A-(1-11) (IC50 46 nM). The affinity of dynorphin la for the κ site in the guinea pig cerebellum (Ki 0.25 nM) was comparable to those of dynorphin A-(l–13) (Ki 0.11 nM) and [D-Pro10]dynorphin A-(1-11) (Ki 0.10 nM). However, the peptide possessed reduced affinities for the μ (Ki 6.7 nM) and δ (Ki 71 nM) opioid receptors as compared with [D-Pro10]dynorphin A-(1-11) (Ki 1.7 and 1.5 nM) an dynorphin A-(l-13) (Ki 0.5 and 4.4 nM, respectively). Finally, low doses (2.2–8.8 nmol) of intrathecal dynorphin la caused a potent and selective antinociceptive effect in the paw-pressure assay and did not impair motor activity or cause any significant change of blood pressure. These results indicate that dynorphin la possesses the biological profile of a potent and selective κ opioid agonist.

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