Gamma-hydroxybutyrate increases gastric emptying in rats

Effects of β‑hydroxybutyric acid and ghrelin on the motility and inflammation of gastric antral smooth muscle cells involving the regulation of growth hormone secretagogue receptor

Ghrelin is an orexigenic hormone that is produced by gastric cells. Ghrelin stimulates food intake and increases gastric movement. In rat model, injected β‑hydroxybutyric acid (β‑HB) leads to a decrease in body weight. It has been reported that patients with gastric erosions are slower to evacuate the stomach. The aim of the present study was to investigate the effects of ghrelin and β‑HB on motility and inflammation in rat gastric antral smooth muscle cells (GASMCs). GASMCs were extracted from rat gastric antrum. Cell viability was determined using the Cell Counting Kit‑8 assay. A reactive oxygen species (ROS) assay kit was used to analyze the levels of ROS using flow cytometry. Protein levels were determined using western blotting, and the expression levels of mRNAs were evaluated using reverse transcription‑quantitative PCR. β‑HB inhibited the expression of myosin regulatory light polypeptide 9 (MYL9), myosin light chain kinase (MLCK), transforming protein RhoA (RhoA), Rho‑associated protein kinase‑1 (ROCK‑1) and growth hormone secretagogue receptor (GHS‑R). By contrast, ghrelin increased the expression of MYL9, MLCK, RhoA, ROCK‑1 and GHS‑R in β‑HB‑treated GASMCs. β‑HB increased the levels of tumor necrosis factor (TNF)‑α, interleukin (IL)‑6 and ROS, and decreased the levels of manganese (Mn) superoxide dismutase (SOD), copper/zinc (Cu/Zn)SOD and catalase. Ghrelin decreased the expression of TNF‑α, IL‑6, ROS and catalase, whereas ghrelin promoted the expression of MnSOD and Cu/ZnSOD in β‑HB‑treated GASMCs. Short interfering RNA targeting GHS‑R inhibited the expression of MYL9, MLCK, RhoA and ROCK‑1, and increased the levels of TNF‑α, IL‑6 and ROS in β‑HB‑treated or ghrelin‑treated GASMCs. The present study provided preliminary evidence that β‑HB inhibits the motility of GASMCs and promotes inflammation in GASMCs, whereas ghrelin decreases these effects. GHS‑R acted as a primary regulator of motility and inflammation in GASMCs treated with β‑HB and ghrelin.

Toxicologic/transport properties of NCS-382, a γ-hydroxybutyrate (GHB) receptor ligand, in neuronal and epithelial cells: Therapeutic implications for SSADH deficiency, a GABA metabolic disorder

We report the in vitro assessment of pharmacotoxicity for the high-affinity GHB receptor ligand, NCS-382, using neuronal stem cells derived from mice with a targeted deletion of the aldehyde dehydrogenase 5a1 gene (succinic semialdehyde dehydrogenase(SSADH)-deficient mice). These animals represent a phenocopy of the human disorder of GABA metabolism, SSADH deficiency, that metabolically features accumulation of both GABA and the GABA-analog γ-hydroxybutyric acid in conjunction with a nonspecific neurological phenotype. We demonstrate for the first time using MDCK cells that NCS-382 is actively transported and capable of inhibiting GHB transport. Following these in vitro assays with in vivo studies in aldh5a1^-/- mice, we found the ratio of brain/liver GHB to be unaffected by chronic NCS-382 administration (300mg/kg; 7 consecutive days). Employing a variety of cellular parameters (reactive oxygen and superoxide species, ATP production and decay, mitochondrial and lysosomal number, cellular viability and necrosis), we demonstrate that up to 1mM NCS-382 shows minimal evidence of pharmacotoxicity. As well, studies at the molecular level indicate that the effects of NCS-382 at 0.5mM are minimally toxic as evaluated using gene expression assay. The cumulative data provides increasing confidence that NCS-382 could eventually be considered in the therapeutic armament for heritable SSADH deficiency.

Intragastric infusion of pea-protein hydrolysate reduces test-meal size in rats more than pea protein

Because protein hydrolysates are digested faster than the corresponding proteins, they may increase or hasten the acute eating-inhibitory effect of protein. Potential mediating mechanisms include accelerated or greater release of satiating gut peptides and activation of metabolic signals that inhibit eating. We tested these hypotheses in adult male rats that were surgically equipped with intragastric (IG) cannulas and adapted to 30-min test meals at dark onset after 14-h food deprivation. Equiosmotic 12 ml loads of saline-urea control (C), 13.6% pea protein (PP), or 13.6% PP hydrolysate (PPH, DSM/DFS, Delft, The Netherlands) solutions were IG infused in 1 min just before test meals. PPH reduced test-meal size compared to C more than PP (-3.8±0.3 g vs. -2.6±0.4 g; P<0.0001). Plasma glutamate increased more after PPH than PP (P<0.0001). Plasma lactate, alanine, insulin, glucagon, GLP-1 and paracetemol (an index of gastric emptying) all increased similarly, and glucose decreased similarly, after PPH or PP. Finally, PPH still reduced test-meal size more than PP (-4.6±0.3 g vs. -3.1±0.4 g; P<0.001) in rats after subdiaphragmatic vagal deafferentation, indicating that abdominal vagal afferents are not necessary for the eating-inhibitory effects of PP and PPH and, by extension, that gut peptides whose satiating effects depend on intact vagal afferents (e.g., CCK and glucagon) do not play crucial roles. Thus, PPH reduced short-term food intake more than PP under our conditions, but the mechanism(s) involved remain unclear.

Behavioral analyses of GHB: receptor mechanisms

GHB is used therapeutically and recreationally, although the precise mechanism of action responsible for its different behavioral effects is not entirely clear. The purpose of this review is to summarize how behavioral procedures, especially drug discrimination procedures, have been used to study the mechanism of action of GHB. More specifically, we will review several different drug discrimination procedures and discuss how they have been used to qualitatively and quantitatively study different components of the complex mechanism of action of GHB. A growing number of studies have provided evidence that the behavioral effects of GHB are mediated predominantly by GABAB receptors. However, there is also evidence that the mechanisms mediating the effects of GHB and the prototypical GABAB receptor agonist baclofen are not identical, and that other mechanisms such as GHB receptors and subtypes of GABAA and GABAB receptors might contribute to the effects of GHB. These findings are consistent with the different behavioral profile, abuse liability, and therapeutic indications of GHB and baclofen. A better understanding of the similarities and differences between GHB and baclofen, as well as the pharmacological mechanisms of action underlying the recreational and therapeutic effects of GHB, could lead to more effective medications with fewer adverse effects.

A review of pharmacology of NCS-382, a putative antagonist of gamma-hydroxybutyric acid (GHB) receptor

Gamma-hydroxybutyric acid (GHB), a naturally occurring metabolite of gamma-aminobutyric acid (GABA), has been postulated to act as a specific agonist of GHB receptors and as well as a weak GABA(B) receptor agonist. To date, 6,7,8,9-tetrahydro-5-hydroxy-5H-benzocyclohept-6-ylideneacetic acid (NCS-382), a semirigid compound structurally related to GHB, is the only compound reported to be an antagonist of the GHB receptor sites. In this article we review the in vivo and in vitro pharmacological properties of NCS-382 and its interaction with GHB and GABA(B) receptors. Binding studies have demonstrated that NCS-382 is a stereoselective ligand for GHB-binding sites, with both, the high and the low component of population, showing the same distribution of GHB receptors. Indeed, this compound did not display affinity for GABA(A), GABA(B), or any other known receptors, while conflicting data have been reported as to its selective antagonist action at GHB receptor. Only a few studies have shown that NCS-382 antagonizes GHB-induced effect, but a re-evaluation of all data reported in the literature suggests that the antagonistic effect of this compound could be due to an indirect action at GABA(B) receptors. As revealed by several behavioral studies, NCS-382 fails to antagonize GHB discriminative stimuli, GHB-induced inhibition of locomotor activity and ataxia or suppression of operant responses. Moreover, it is capable of either eliciting qualitatively similar effects to those of GHB or enhancing some actions of GHB. In addition, the NCS-382-sensitive electrophysiological effects of endogenous and exogenous GHB observed in vivo have not been completely replicated in vitro. The only electrophysiological action of GHB antagonized in vitro by NCS-382 required a previous blockade of GABA(B) receptors. We concluded that NCS-382 is a good ligand but not a selective antagonist for GHB receptor.

Effects of an aldose reductase inhibitor on gastroenteropathy in streptozotocin-diabetic rats

We investigated the effects of epalrestat, an aldose reductase inhibitor (ARI), on gastric emptying, fecal water content, and electrolyte transport in distal colon in streptozotocin (STZ)-induced diabetic rats. We measured gastric emptying time by acetaminophen method and short-circuit-current (Isc) in colonic mucosa using an Ussing chamber. The Isc in response to electric-field-stimulation (EFS) was decreased in untreated rats due to suppression by Cl- secretion. ARI treatment alleviated this suppression (2.7 +/- 0.6 vs. 7.4 +/- 1.1 microA/0.38 cm2 at 8 weeks after treatment, 1.1 +/- 0.2 vs. 7.0 +/- 1.0 at 12 weeks after treatment, P<0.05). In addition, the percentage of fecal water content in untreated rats was significantly lower than in ARI-treated rats (58.0 +/- 2.0 vs. 67.6 +/- 0.8% at 8 weeks, 56.9 +/- 2.1 vs. 63.4 +/- 1.4 at 12 weeks, P<0.05). From STZ injection to 8 weeks, the serum levels of acetaminophen in the diabetic rats were significantly lower than in controls, indicating delayed gastric emptying. At 12 weeks in the diabetic rats treated with ARI, the serum levels of acetaminophen were significantly higher than in the untreated diabetic rats (6.6 +/- 0.4 vs. 3.5 +/- 0.5 microg/ml, P<0.05). ARI-treatment ameliorated delayed gastric emptying without improving glycemic control. These findings show that ARI partially prevented progression of impaired gastric emptying, ion transport, and water transport, and suggest that epalrestat might be useful in the treatment of diabetic gastroenteropathy.

Endogenous gamma-hydroxybutyric acid is in the rat, mouse and human gastrointestinal tract

By using Gas Chromatography-Mass Spectrometry high concentrations of endogenous gamma-hydroxybutyric acid (GHB) have been demonstrated in the rat and mouse gastrointestinal tract, including stomach, small intestine and colon-rectum. GHB concentrations were many folds higher than those present in the brain. High GHB concentrations have been also found in the human operatory specimen of sigmoid colon. Since GHB administration has been found to modify gastrointestinal motility via GABA(B) receptors, the present results suggest that endogenous GHB might be involved in the GABA(B) receptor-mediated control of gastrointestinal function.

GABA(B)-receptor mediation of the inhibitory effect of gamma-hydroxybutyric acid on intestinal motility in mice

The effect of acutely administered gamma-hydroxybutyric acid (GHB) and GHB receptor antagonist, NCS-382, on the propulsive activity in the mouse small intestine was assessed by measuring the transit of an orally administered, non absorbable marker. Both GHB (0, 25, 50, 100, 200 and 300 mg/kg; i.p.) and NCS-382 (0, 25, 50 and 75 mg/kg; i.p.) induced a dose-dependent inhibition (up to 50-60%) of the marker transit. Pretreatment with the GABA(B) receptor antagonist, SCH 50911 (100 mg/kg; i.p.), resulted in the blockade of the inhibiting effect of both GHB and NCS-382. These results suggest that the constipating effect of GHB and NCS-382 are secondary to stimulation of the GABA(B) receptor.

Role of GABA(B) receptors in the sedative/hypnotic effect of gamma-hydroxybutyric acid

The present study was aimed at identifying the receptor systems involved in the mediation of the sedative/hypnotic effect of gamma-hydroxybutyric acid (GHB) in DBA mice. Administration of the putative antagonist of the GHB binding site, 6,7,8,9-tetrahydro-5-hydroxy-5H-benzocyclohept-6-ylideneacetic acid (NCS-382; 50-500 mg/kg, i.p.), significantly increased the duration of loss of righting reflex induced by GHB (1000 mg/kg, i.p.). In contrast, the GABA(B) receptor antagonists, (2S)(+)-5,5-dimethyl-2-morpholineacetic acid (SCH 50911; 25-100 mg/kg, i.p.) and (3-aminopropyl)(cyclohexylmethyl)phosphinic acid (CGP 46381; 12.5-150 mg/kg, i.p.), completely prevented the sedative/hypnotic effect of GHB. SCH 50911 (100 and 300 mg/kg, i.p.) was also capable to readily reverse the sedative/hypnotic effect of GHB (1000 mg/kg, i.p.) in mice that had lost the righting reflex. SCH 50911 (100 mg/kg, i.p.) also completely abolished the sedative/hypnotic effect of the GABA(B) receptor agonist, baclofen. These results indicate that the sedative/hypnotic effect of GHB is mediated by the stimulation of GABA(B) receptors and add further support to the hypothesis that the GABA(B) receptor constitutes a central site of action of GHB.