Detection of gamma-hydroxybutyrate in striatal microdialysates following peripheral 1,4-butanediol administration in rats

Concentration-effect relationships for the drug of abuse gamma-hydroxybutyric acid

gamma-Hydroxybutyric acid (GHB) is an endogenous neurotransmitter that is abused because of its sedative/hypnotic and euphoric effects. The objectives of this study were to evaluate the concentration-effect relationships of GHB in plasma, cerebrospinal fluid (CSF), brain (whole and discrete brain regions), and brain frontal cortex extracellular fluid. This information is crucial for future studies to evaluate effects of therapeutic interventions on the toxicodynamics of GHB. GHB (200-1000 mg/kg) was administered intravenously to rats, and plasma and frontal cortex microdialysate samples were collected for up to 6 h after the dose, or plasma, CSF, and brain (whole, frontal cortex, striatum, and hippocampus) concentrations were determined at the offset of its sedative/hypnotic effect [return to righting reflex (RRR)]. GHB-induced changes in the brain neurotransmitters gamma-aminobutyric acid (GABA) and glutamate were also determined. GHB, GABA, and glutamate concentrations were measured by liquid chromatography/tandem mass spectrometry. GHB-induced sleep time significantly increased in a dose-dependent manner (20-fold increase from 200 to 1000 mg/kg). GHB concentrations in plasma (300-400 microg/ml), whole brain (70 microg/g), discrete brain regions (80-100 microg/g), and brain microdialysate (29-39 microg/ml) correlated with RRR. In contrast, CSF GHB and GABA and glutamate concentrations in discrete brain regions exhibited no relationship with RRR. Our results suggest that GHB-induced sedative/hypnotic effects are mediated directly by GHB and that at high GHB doses, GABA formation from GHB may not contribute to the observed sedative/hypnotic effect. These results support the use of a clinical GHB detoxification strategy aimed at decreasing plasma and brain GHB concentrations after GHB overdoses.

Effects of L-lactate and D-mannitol on gamma-hydroxybutyrate toxicokinetics and toxicodynamics in rats

Overdoses of gamma-hydroxybutyrate (GHB), a drug of abuse, result in coma, respiratory arrest, and death. The objective of this study was to evaluate a potential GHB detoxification strategy by inhibiting the monocarboxylate transporter (MCT)-mediated renal reabsorption of GHB in rats, using the MCT substrate L-lactate. The use of the osmotic diuretic D-mannitol alone or combined with L-lactate was also explored. GHB (208 mg/h/kg) was infused i.v. for 3 h in the absence or presence of L-lactate (60.5, 121, and 302.5 mg h(-1) kg(-1)), D-mannitol (0.5 g/kg), or L-lactate (60.5 mg h(-1) kg(-1)) combined with D-mannitol (0.5 g/kg). GHB in plasma and urine samples was determined along with blood pH, electrolytes, glucose, and L-lactate. Administration of L-lactate, or the combination of L-lactate and D-mannitol, but not D-mannitol alone, significantly increased the renal and total clearances of GHB in rats. Blood pH and electrolyte concentrations exhibited small changes with GHB, GHB/lactate, and GHB/mannitol treatments, although most values remained within their normal range. The concomitant administration of lactated Ringer's solution (28 mM L-lactate) at 300 mul/min with mannitol (0.5 g/kg) resulted in a significant increase in GHB clearance and a decrease in sleep time after an i.v. dose of 1 g/kg. Overall, our results indicated the following: 1) the use of the MCT inhibitor L-lactate can increase the renal and total clearances of GHB, and 2) the combination of lactated Ringer's solution and D-mannitol significantly alters GHB toxicokinetics and toxicodynamics and represents a potential clinical detoxification strategy for the treatment of GHB overdoses.