Beta-endorphin C-terminal peptide evokes arachidonic acid release from cortical neurones

Glycyl-glutamine inhibits nicotine conditioned place preference and withdrawal

Glycyl-glutamine (Gly-Gln) is an inhibitory dipeptide synthesized from beta-endorphin(1-31). Previously, we showed that Gly-Gln inhibits morphine conditioned place preference, tolerance, dependence and withdrawal. In this study, we tested whether Gly-Gln's inhibitory activity extends to other rewarding drugs, specifically nicotine. Rats were conditioned with nicotine (0.6 mg/kg, s.c.) for four days and tested on day five. Glycyl-glutamine (100 nmol i.c.v.) inhibited acquisition and expression of a nicotine place preference significantly. Cyclo(Gly-Gln) (100 nmol i.c.v. or 25 mg/kg i.p.), a cyclic Gly-Gln derivative, blocked expression of nicotine place preference but Gly-d-Gln (100 nmol i.c.v.) was ineffective. To study nicotine withdrawal, rats were treated with nicotine (9 mg/kg/day) for seven days and conditioned place aversion was induced with mecamylamine (1 mg/kg, s.c.). Glycyl-glutamine blocked acquisition of place aversion to mecamylamine but not U50,488, a kappa opioid receptor agonist. Glycyl-glutamine thus inhibits the rewarding effects of nicotine and attenuates withdrawal in nicotine dependent rats.

Inhibition of interleukin-1beta and prostaglandin E(2) thermogenesis by glycyl-glutamine, a pro-opiomelanocortin-derived peptide

Interleukin-1beta (IL-1beta) and other cytokines produce fever by stimulating prostaglandin E(2) (PGE(2)) synthesis in thermoregulatory regions of the preoptic area and anterior hypothalamus (POA/AH). Prostaglandin E(2) is thought to raise body temperature, at least in part, by stimulating beta-endorphin release from pro-opiomelanocortin neurons that innervate the POA/AH. In this study, we investigated whether glycyl-glutamine (beta-endorphin(30-31)), an inhibitory dipeptide synthesized from beta-endorphin post-translationally, inhibits IL-1beta and PGE(2)-induced hyperthermia. Hyperthermic sites were identified by microinjecting PGE(2) (3 fmol/1 microl) into the medial preoptic area (mPOA) of conscious, unrestrained rats. Interleukin-1beta (1 U) injection into the same PGE(2) responsive thermogenic sites in the mPOA elicited a prolonged rise in colonic temperature (T(c)) (+1.02+/-0.06 degrees C) that persisted for at least 2 h. Glycyl-glutamine (3 nmol) co-injection into the mPOA inhibited IL-1beta thermogenesis completely (T(c)=-0.18+/-0.22 degrees C). Glycyl-glutamine had no effect on body temperature when given alone to normothermic rats. Co-injection of individual amino acids, glycine and glutamine (3 nmol each amino acid), failed to influence IL-1beta-induced thermogenesis, which indicates that Gly-Gln hydrolysis does not explain its inhibitory activity. Glycyl-glutamine (3 nmol) also prevented the rise in body temperature produced by PGE(2) (PGE(2)=0.89+/-0.05 degrees C; PGE(2) plus Gly-Gln=-0.16+/-0.14 degrees C), consistent with evidence that PGE(2) mediates IL-1beta-induced fever. These findings demonstrate that Gly-Gln inhibits the thermogenic response to endogenous pyrogens.

Glycyl-glutamine inhibits the respiratory depression, but not the antinociception, produced by morphine

Glycyl-glutamine (Gly-Gln; beta-endorphin(30-31)) is an endogenous dipeptide that is synthesized through the posttranslational processing of beta-endorphin in brain stem regions that control respiration and autonomic function. This study tested the hypothesis that Gly-Gln administration to conscious rats will prevent the respiratory depression caused by morphine without affecting morphine antinociception. Rats were administered Gly-Gln (1-100 nmol) or saline (10 microl) intracerebroventricularly followed, 5 min later, by morphine (40 nmol icv). Arterial blood gases and pH were measured immediately before Gly-Gln and 30 min after morphine injection. Gly-Gln pretreatment inhibited morphine-induced hypercapnia, hypoxia, and acidosis significantly. The response was dose dependent and significant at Gly-Gln doses as low as 1 nmol. In contrast, Gly-Gln (1-300 nmol) had no effect on morphine-evoked antinociception in the paw withdrawal test. When given alone to otherwise untreated animals, Gly-Gln did not affect nociceptive latencies or blood gas values. These data indicate that Gly-Gln inhibits morphine-induced respiratory depression without compromising morphine antinociception.

Glycyl-L-glutamine [beta-endorphin-(30-31)] attenuates hemorrhagic hypotension in conscious rats

The profound hypotension caused by acute hemorrhage is thought to involve opioid peptide neurons. In this study, we tested whether glycyl-L-glutamine [Gly-Gln; beta-endorphin-(30-31)], a nonopioid peptide derived from beta-endorphin processing, prevents the cardiovascular depression induced by hemorrhage in conscious and anesthetized rats. Previously, we found that Gly-Gln inhibits the hypotension and respiratory depression produced by beta-endorphin and morphine but does not affect opioid antinociception. Hemorrhage (2.5 ml/100 g body wt over 20 min) lowered arterial pressure in conscious rats (from 120.1 +/- 2.9 to 56.2 +/- 4.7 mmHg) but did not change heart rate significantly. Intracerebroventricular Gly-Gln (3, 10, or 30 nmol) pretreatment inhibited the fall in arterial pressure and increased heart rate significantly. The response was dose related and was sustained during the 35-min posthemorrhage interval. Pentobarbital sodium anesthesia potentiated the hemodynamic response to hemorrhage and attenuated the effect of Gly-Gln. Gly-Gln (10 or 100 nmol icv) did not influence arterial pressure or heart rate in normotensive rats. These data indicate that Gly-Gln is an effective antagonist of hemorrhagic hypotension.

Cerebrospinal and plasma amino acid concentrations after administration of i.v. glycyl-glutamine and glycyl-tyrosine containing amino acid solutions in humans

BACKGROUND

Glycyl-glutamine and glycyl-tyrosine may supply adequate glutamine and tyrosine in amino acid solutions for parenteral nutrition. However, plasma peptides may be transported into the cerebrospinal fluid, exerting effects on the neuronal tissue. Cerebrospinal fluid (CSF) and plasma amino acid concentrations after administration of a glycyl-glutamine/glycyltyrosine supplemented amino acid solution were therefore evaluated in a randomized controlled comparison with a conventional amino acid infusion.

METHODS

Dipeptide/amino acid solutions (0.60 mL/h/kg; 82.2 mg total dipeptides/amino acids/h/kg) or conventional amino acid solutions (0.73 mL/h/kg; 83.2 mg total amino acids/h/kg) were infused in 15 patients per group scheduled to undergo spinal anesthesia for urologic surgery over a 12-hour period preoperatively. Plasma amino acids were measured before the infusion was started. CSF and venous concentrations were analyzed simultaneously before the infusion was stopped. CSF samples were drawn through the spinal needle for anesthesia.

RESULTS

The dipeptide-containing solution did not increase either dipeptide to detectable levels in the CSF (detection limit < 5.0 nmol/mL). Venous glycyl-glutamine increased from below detection limits up to 308 +/- 111 nmol/mL (p < .05), whereas glycyl-tyrosine could not be found. In the dipeptide group, venous glutamine and tyrosine were higher (p < .05) but only tyrosine appeared in small amounts (p < .05) in the cerebrospinal fluid.

CONCLUSIONS

This study provides no evidence to support a CSF entry of IV glycyl-tyrosine and glycyl-glutamine under conditions of a normal blood-brain barrier in the adult (detection limit 5 nmol/mL). The data suggest that amino acid solutions containing these dipeptides may be used in parenteral solutions for nutrition support.

Glycyl-L-glutamine antagonizes alpha-MSH-elicited thermogenesis

The objective of this study was to determine whether glycyl-L-glutamine [beta-endorphin(30-31)] modulates the thermoregulatory actions of alpha-MSH. Microinjection of alpha-MSH (0.06 nmol) into PGE2-responsive thermogenic sites in the medial preoptic area of rats generated a hyperthermic response, inducing a 0.85 +/- 0.19 degrees C rise in colonic temperature (Tc) within 45 min. Coadministration of glycyl-L-glutamine (3.0 nmol) completely blocked the response, maintaining Tc at baseline levels. This was not attributable to glycyl-L-glutamine hydrolysis because coadministration of glycine and glutamine had no effect on alpha-MSH-induced thermogenesis. Glycyl-L-glutamine, injected alone, was similarly without effect. These data indicate that glycyl-L-glutamine inhibits alpha-MSH-induced thermogenesis but is devoid of thermoregulatory activity itself.