The effects of opioid antagonists on ingestive behavior in the domestic fowl

The effects of opioid antagonists on food and water intake in commercial stocks of chickens were investigated. Four experiments were conducted to examine the effects of naloxone (N-allylnoroxymorphone) and naltrexone (N-cyclopropylnoroxymorphone) in broiler and Single-Comb White Leghorn cockerels. Birds were injected intramuscularly with either naloxone HCl or naltrexone HCl at doses from 2.5 to 10 mg/kg. Food and water were offered ad lib 15 min post-injection. In broilers, naloxone dose-dependently attenuated food and water consumption for 300 min, while in Leghorns naloxone attenuated food and water intake for 240 and 300 min, respectively. Naltrexone dose-dependently reduced food and water consumption for 300 min in both broilers and Leghorns. Neither naloxone nor naltrexone significantly altered food or water intake at 24 hr. A fifth experiment was conducted to verify the specificity of opioid antagonism for water intake. Broiler cockerels received an intraperitoneal injection of either isotonic saline (0.15 M NaCl) or hypertonic saline (2.5 M NaCl) followed by an intramuscular injection of either isotonic saline or naloxone HCl (5 mg/kg). Food was withheld for the entire experiment while water was offered ad lib 15 min following the second injection. Naloxone significantly attenuated drinking in normally hydrated and osmotically challenged birds for 150 min. The results suggest a role for endogenous opioid peptides in the regulation of food and water intake in meat and egg-laying stocks of chickens.

Beta-endorphin: peripheral opioid activity of homologues from six species

The peripheral opioid activity of six homologous beta-endorphins (beta-EPs) were assayed on the guinea pig ileum and the vas deferens of the mouse, the rat and the rabbit. In the guinea pig ileum assay, human beta-EP (beta h-EP) was less potent than camel, turkey, and ostrich beta-EPs, of the same potency as equine beta-EP and more active than des-acetyl salmon beta-EP. In the rat vas deferens, mammalian beta-EPs showed higher activity than those from the bird and the fish, whereas in the mouse vas deferens assay, beta h-EP is more active than those from other species. In the rabbit vas deferens, however, all homologous beta-EPs show very weak activity. The relative potency of beta-EP homologues obtained from rat vas deferens assay is in good correlation with the analgesic potency, while the receptor binding activity does not correlate with any of the four bioassays, but appears to be related to the charge properties of the peptides.

Intracerebroventricular injection of ostrich beta-endorphin to satiated pigeons induces hyperphagia but not hyperdipsia

Satiated pigeons received intracerebroventricular injections of either ostrich (0.06, 0.3 and 1.5 nmoles) or human (0.06 and 1.5 nmoles) beta-endorphin, or a control solution, and their consumption of food and water was monitored during the half hour after these treatments. At each administered dose, ostrich beta-endorphin enhanced food without altering water intake. By contrast, human beta-endorphin did not induce any reliable alteration either of feeding or drinking. Together with previous studies performed in pigeons with opiate antagonists, these results suggest that the feeding system of pigeons is modulated by an endorphinergic mechanism. By contrast, no evidence exists so far that such a mechanism operates for controlling drinking, as appears to be the case in mammals.

Beta-endorphin: demonstration of binding sites in three human neuroblastoma cell lines specific for the COOH-terminal segment of the human hormone

This communication reports for the first time specific binding sites in human neuroblastoma cells for human beta-endorphin (beta h-EP). Three cell lines (IMR-32, NMB and Kelly) were investigated and found to bind tritiated beta h-EP with an apparent dissociation constant of 2.2-4.2 nM. Further characterization with camel beta-EP and synthetic analogs indicated that the binding is most likely mediated by the COOH-terminal segments. beta h-EP-(6-31) had significant potency (15-75%) and beta h-EP-(1-27) was without displacing activity. The camel beta-EP has below 1% of the human beta-EP activity.

beta-Endorphin: analgesic and receptor binding activity of non-mammalian homologs

Analgesic potencies of turkey, ostrich and des-acetyl salmon beta-endorphins have been measured in the tail-flick test and binding affinities determined by radio-receptor assay. The duration of analgesia and the slope of the dose-response curves generated by these peptides are similar to those elicited by mammalian beta-endorphins. This suggests that they act in vivo and in vitro on the same population of opiate receptors. The ratio of binding to analgesic potencies observed for these peptides varies nearly sixfold. Structure-activity analysis suggests that a basic side-chain at position 9 is required in order to produce a high opiate activity both in vivo and in vitro. A reexamination of the biological activities of camel beta-endorphin shows that the analgesic potency and binding affinity of this peptide are respectively 171 and 2.7 times higher than human beta-endorphin. His-27 and/or Gln-31 may contribute to this increased potency. The dissociation of radioreceptor binding affinity from analgesic potency in these naturally occurring beta-endorphin homologs suggests that either the conditions under which the binding assay is performed mask the true binding potency in the brain or that, once bound to the appropriate receptor, these homologs do not possess equal ability to produce biological effects.