Enkephalin heptapeptide (Tyr-Gly-Gly-Phe-Met-Arg-Phe)-induced bronchospasm in guinea pigs: a non-naloxone reversible phenomenon

Mu-opioid receptor activation in live cells

Interaction of the mu-opioid receptor (MOP) with selected ligands was investigated in live cells using advanced imaging by confocal laser scanning microscopy integrated with fluorescence correlation spectroscopy and fluorescence cross-correlation spectroscopy. In PC12 cells stably transformed to express the fluorescently labeled MOP-enhanced green fluorescent protein construct, two pools of MOP were identified that could be discriminated by differences in their lateral mobility in the cell membrane. The majority of MOP receptors (80+/-10%) were characterized by a diffusion coefficient D(MOP,1) = (4+/-2) x 10(-11) m(2) s(-1), compared with the slowly moving fraction, D(MOP,2) = (4+/-2) x 10(-12) m(2) s(-1). On stimulation with selected agonists ([D-Ala(2),N-MePhe(4),Gly-ol(5)]enkephalin, enkephalin-heptapeptide Tyr-Gly-Gly-Phe-Met-Arg-Phe, morphine, and methadone), surface density of the MOP decreased, whereas the lateral mobility increased. In contrast, antagonists (naloxone and naltrexone) "froze" the receptor in the membrane, i.e., increased MOP surface density and decreased lateral mobility. Agonist activation was also accompanied by pronounced changes in the dynamics of plasma membrane lipids, as revealed by the general lipid marker 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate dye. The results provide new information about MOP activation in live cells at the molecular level, with a special focus on the dynamics of the intricate interplay between this receptor and the surrounding lipids.

Enkephalin-like immunoreactivity in ganglionic cells in the larynx and superior cervical ganglion of the rat

The distribution of enkephalin-like immunoreactivity (ENK-LI) in the larynx, the superior cervical ganglion (SCG) and the nodose ganglion of adult rats was examined in the present study. A substantial number of the local acetylcholinesterase (AChE)-positive, presumably parasympathetic, ganglionic cells in the larynx displayed ENK-LI. These cells also exhibited neuropeptide Y (NPY)- and vasoactive intestinal polypeptide (VIP)-LI. Varicose nerve fibers showing ENK-LI were observed close to the acini and ducts of the glands, in the perichondrium and in the lamina propria. The varicosities exhibiting ENK-LI frequently displayed NPY- and VIP-LI. The ENK-LI was detected in a subpopulation of AChE-positive nerve fibers in the laryngeal tissue. In the SCG, only a small number of the ganglionic cells displayed ENK-LI. These cells, in contrast to other ganglionic cells of the SCG, did not show NPY-LI. None of the ganglionic cells of the nodose ganglion exhibited ENK-LI. Sympathectomy and vagotomy affected neither the number nor the distribution of fibers showing ENK-LI in the larynx. In conclusion, ENK appears to be present together with NPY and VIP in the parasympathetic innervation of the larynx and in a very limited number of the ganglionic cells of a sympathetic ganglion, the SCG, of the adult rat.

The effects of endorphins on mucous glycoprotein secretion from feline airways in vitro

The effect of opioid peptide hormones on respiratory glycoprotein secretion was investigated in a cat tracheal organ culture system. Dynorphin A (dyn, 10(-5) M), alpha-endorphin (alpha E, 10(-5) M) and morphine sulfate (MS, 10(-4) M) stimulated mucous glycoprotein (MGP) release from airways, whereas all other endorphins tested failed to have such an effect. Dyn did so in a dose dependent manner (10(-5)-10(-7) M) with a peak effect after a one hour incubation. Two sets of data suggest that dyn is acting through the previously described endorphin-kappa receptor: The active binding site of dyn is at the carboxyl end of the peptide; dyn fragment 1-13 stimulated MGP secretion while dyn fragment 1-8 did not. Naloxone in equimolar concentration totally inhibited the dyn response. We, therefore, conclude that the endorphins dyn and alpha E stimulate MGP release and that dyn is probably acting by stimulating kappa receptors.

The effect of enkephalins and prostaglandins on O-2 release by neutrophils

Derivatives of superoxide (O-2), produced by phagocytic cells, are thought to play a role in the adult respiratory distress syndrome (ARDS) and other disease states. Control of the release of O-2 may prove beneficial. Using human neutrophils as a source of O-2, and an assay for O-2 based upon the reduction of cytochrome C, we found that prostaglandin D2 (PGD2), leucine enkephalin (LE), and methionine enkephalin (ME) inhibited O-2 release. The Escherichia coli product, N-formyl methionyl leucyl phenylalanine (FMLP), was employed to stimulate O-2 release. PGD2 was most potent while there was no significant difference between LE and ME. Another peptide, thyrotropin releasing hormone (TRH), had no effect on O-2 release. There was no correlation between the potency of the inhibitory effect on O-2 release and the effect of these agents on the binding of [3H] FMLP to human neutrophils. Comparison of different but structurally related prostaglandins (PGD2, PGE2, and PGF2 alpha) revealed that PGD2 was more potent than PGE2 in inhibiting O-2 and that PGF2 alpha had no effect. This result suggested that the presence and position of the carbonyl group was an important determinant of the magnitude of inhibition.

Enkephalin-degrading dipeptidyl carboxypeptidase in guinea pig serum: its properties and action on bioactive peptides

A dipeptidyl carboxypeptidase, which cleaved the Gly3-Phe4 bond of enkephalins, was purified from guinea pig serum 420-fold. The optimum pH of the enzyme was in the neutral range (pH 7.25), and the molecular weight was estimated to be approx. 280,000. The enzyme hydrolyzed Met- and Leu-enkephalin with Km values of 0.30 and 0.50 mM, respectively. The enzyme was inhibited by metal chelators and p-chloro-mercuribenzoate. Captopril showed high inhibitory potency, while phosphoramidon and Phe-Ala showed no effect on the enzyme activity. Therefore, the obtained enzyme can be classified as an angiotensin-converting enzyme (EC 3.4.15.1). Among the bioactive peptides examined, bradykinin and angiotensin I were hydrolyzed by the enzyme. Angiotensin III showed a stronger inhibitory effect than that of angiotensin II. Substance P, gastrin I, and secretin were also inhibitory toward the enzyme activity. On high-performance liquid chromatography analysis, Met-enkephalin-Arg6-Phe7 and Leu-enkephalin-Arg6 were cleaved sequentially at the second peptide bond of the C terminus. Thus, the dipeptidyl carboxypeptidase in guinea pig serum may play a role not only in the angiotensin-bradykinin system but also in the metabolism of circulating enkephalins and other bioactive peptides.