enkephalin--leucine-2-alanine and dynorphin-(1-8)

We hypothesized that, in the airway mucosa, opioids are inhibitory neural modulators that cause an increase in net water absorption in the airway mucosa (as in the gut). Changes in bidirectional water fluxes across ovine tracheal mucosa in response to basolateral application of the opioid peptides beta-endorphin, dynorphin A-(1-8), and [d-Ala(2), d-Leu(5)]-enkephalin (DADLE) were measured. beta-Endorphin and dynorphin A-(1-8) decreased luminal-to-basolateral water fluxes, and dynorphin A-(1-8) and DADLE increased basolateral-to-luminal water flux. These responses were electroneutral. In seven beagle dogs, administration of aerosolized beta-endorphin (1 mg) to the tracheobronchial airways decreased the clearance of radiotagged particles from the bronchi in 1 h from 34.7 to 22.0% (P < 0.001). Naloxone abrogated the beta-endorphin-induced changes in vitro and in vivo. Contrary to our hypothesis, the opioid-induced changes in water fluxes would all lead to a predictable increase in airway surface fluid. The beta-endorphin-induced increases in airway fluid together with reduced bronchial mucociliary clearance may produce procongestive responses when opioids are administered as antitussives.

Topics: Aerosols; Animals; beta-Endorphin; Bronchi; Dogs; Drug Synergism; Dynorphins; Enkephalin, Leucine-2-Alanine; In Vitro Techniques; Injections, Intramuscular; Ions; Male; Mucociliary Clearance; Naloxone; Narcotic Antagonists; Peptide Fragments; Sheep; Trachea; Water

The effects of selective opioid receptor agonists and antagonists on neural discharge recorded from carotid body arterial chemoreceptors in vivo were studied in anaesthetized cats. Mean ID50 values were determined for each agonist and used to assess chemodepressant potency on intracarotid (i.c.) injection in animals artificially ventilated with air. [Met]enkephalin, [Leu]enkephalin, [D-Ala2, D-Leu5]enkephalin and [D-Pen2, D-Pen5]enkephalin were more potent chemodepressants than [D-Ala2, Me-Phe4, Gly-ol5]enkephalin, dynorphin (1-8) or ethylketocyclazocine; morphiceptin (mu-agonist) was inactive. The rank order of potency was compatible with the involvement of delta-opioid receptors in opioid-induced depression of chemosensory discharge. ICI 154129, a delta-opioid receptor antagonist, was used in fairly high doses and caused reversible dose-related antagonism of chemodepression induced by [Met]enkephalin. It also antagonized depression caused by single doses of [Leu]enkephalin, [D-Ala2, D-Leu5]enkephalin, [D-Ala2, Me-Phe4, Gly-ol5]enkephalin or dynorphin (1-8). ICI 174864, a more potent and selective delta-opioid receptor antagonist, also antagonized chemodepression induced by [Met]enkephalin or by the selective delta-receptor agonist [D-Pen2, D-Pen5]enkephalin. Comparison of background or 'spontaneous' chemosensory discharge during the 30 min periods immediately before and after injecting ICI 174864 (0.1-0.2 mg kg-1 i.c.) showed a significant increase in discharge in one experiment, but in four others discharge was either unaffected or decreased after the antagonist, which argues against a toxic depression of chemosensors by endogenous opioids under resting conditions in our preparation. Sensitivity of the carotid chemoreceptors to hypoxia (ventilating with 10% O2) was increased significantly after ICI 174864, which could be taken as evidence that endogenous opioids depress chemosensitivity during hypoxia. In contrast, responsiveness to hypercapnia was reduced after the antagonist, implying that endogenous opioids may potentiate chemoreceptor sensitivity during hypercapnia. The results obtained using 'selective' agonists and antagonists provide evidence that depression of chemosensory discharge caused by injected opioids involves a delta type of opioid receptor within the cat carotid body. Endogenous opioids may modulate arterial chemoreceptor sensitivity to physiological stimuli such as hypoxia and hypercapnia.

Topics: Animals; Carotid Body; Cats; Chemoreceptor Cells; Cyclazocine; Dose-Response Relationship, Drug; Dynorphins; Endorphins; Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; Enkephalin, D-Penicillamine (2,5)-; Enkephalin, Leucine; Enkephalin, Leucine-2-Alanine; Enkephalin, Methionine; Enkephalins; Ethylketocyclazocine; Hypercapnia; Hypoxia; Peptide Fragments; Receptors, Opioid

Binding of the opiate antagonists [3H]diprenorphine and [3H]naloxone and of the opioid agonists [3H]Met-enkephalin and [3H]dynorphin(1-8) was studied in a fraction of the rat neurohypophysis containing disconnected oxytocin and vasopressin nerve endings ('neurosecretosomes'). There was specific binding of [3H]diprenorphine in the fraction enriched with neurosecretosomes. This binding was only partially displaceable by naloxone; naloxone binding was stereospecific. Intact and unoxidized [3H]Met-enkephalin was found in the neurosecretosome pellet; binding of the analogue D-Ala-D-Leu-enkephalin was very low. Our data favour the assumption of a direct action of endogenous opioids at the neurosecretory nerve endings.

Topics: Animals; Arginine Vasopressin; Binding Sites; Diprenorphine; Dynorphins; Endorphins; Enkephalin, Leucine; Enkephalin, Leucine-2-Alanine; Enkephalin, Methionine; Male; Naloxone; Oxytocin; Peptide Fragments; Pituitary Gland, Posterior; Rats

The opioid receptor preference of dynorphin A fragments, particularly of dynorphin A-(1-8) (DYN 8), has been evaluated in the mouse vas deferens by means of cross-tolerance studies, by their sensitivity to naloxone antagonism and by the use of the irreversible narcotic antagonist beta-funaltrexamine. The tolerance studies revealed kappa receptor activity for the longer fragments and delta activity for the shorter fragments. DYN 8 displayed kappa as well as delta activity, whereas no interaction with mu receptors was observed. The naloxone sensitivity of dynorphin A and its fragments was low with the exception of DYN 8, that displayed an intermediate sensitivity. There was no indication that this intermediate value for DYN 8 was due to an interaction with mu receptors. This conclusion was strengthened in experiments using beta-funaltrexamine. The kappa and delta activity of DYN 8 does not explain the intermediate sensitivity to naloxone. It is proposed that DYN 8 may interact in the mouse vas deferens with a different opioid receptor than the classical mu, kappa- and delta-type.

Topics: Animals; Drug Tolerance; Dynorphins; Endorphins; Enkephalin, Leucine; Enkephalin, Leucine-2-Alanine; Fentanyl; Male; Mice; Naloxone; Naltrexone; Peptide Fragments; Receptors, Opioid; Receptors, Opioid, delta; Receptors, Opioid, kappa; Receptors, Opioid, mu; Vas Deferens