Chronic intragastric administration of gamma-butyrolactone produces physical dependence in baboons.

RATIONALE: Abuse of gamma-hydroxybutyrate (GHB) and its precursors is a public health concern. Gamma-butyrolactone (GBL) is found in commercially available products and, when ingested, is metabolized to GHB. OBJECTIVE: The goal was to evaluate the physical dependence potential and behavioral effects of GBL. METHODS: Vehicle and then GBL were administered continuously (24 h per da y) in baboons (Papio anubis, n=5) via intragastric catheters. GBL dosing was initiated at 100 mg/kg/day and then progressively increased stepwise by increments of 100 mg/kg to a final dose of 600 mg/kg. The number of food pellets earned, fine-motor task performance, and observed behaviors were used as dependent measures. Precipitated withdrawal was evaluated after administration of GABA-B and benzodiazepine receptor antagonists during chronic GBL dosing (400-600 mg/kg). Spontaneous withdrawal was evaluated after discontinuation of chronic GBL 600 mg/kg. Blood GHB levels were determined during chronic dosing of each GBL dose by isotope dilution assay. RESULTS: Chronic GBL dose-dependently decreased food-maintained behavior, disrupted performance on the fine-motor task, and produced signs of sedation and muscle relaxation. The GABA-B antagonist SGS742 [56 mg/kg, intramuscular (IM)] precipitated a withdrawal syndrome, whereas the benzodiazepine antagonist flumazenil (5 mg/kg, IM) produced little or no effect. Signs of physical dependence were also demonstrated when chronic GBL dosing was discontinued. Analysis of plasma indicated GBL was metabolized to GHB; levels were 825 to 1,690 micromol l(-1) GHB and 2,430 to 3,785 micromol l(-1) GHB after week 1 of 400 and 600 mg/kg/day, respectively. CONCLUSIONS: These data indicate that, like GHB, chronic GBL dosing produced physical dependence that likely involved the GABA-B receptor.

Metabolism of gamma-hydroxybutyrate to d-2-hydroxyglutarate in mammals: further evidence for d-2-hydroxyglutarate transhydrogenase.

gamma-Hydroxybutyratic acid (GHB), and its prodrugs 4-butyrolactone and 1,4-butanediol, represent expanding drugs of abuse, although GHB is also used therapeutically to treat narcolepsy and alcoholism. Thus, the pathway by which GHB is metabolized is of importance. The goal of the current study was to examine GHB metabolism in mice with targeted ablation of the GABA degradative enzyme succinic semialdehyde dehydrogenase (SSADH(-/-) mice), in whom GHB persistently accumulates, and in baboons intragastrically administered with GHB immediately and persistently. Three hypotheses concerning GHB metabolism were tested: (1) degradation via mitochondrial fatty acid beta-oxidation; (2) conversion to 4,5-dihydroxyhexanoic acid (a putative condensation product of the GHB derivative succinic semialdehyde); and (3) conversion to d-2-hydroxyglutaric acid (d-2-HG) catalyzed by d-2-hydroxyglutarate transhydrogenase (a reaction previously documented only in rat). Both d-2-HG and 4,5-dihydroxyhexanoic acid were significantly increased in neural and nonneural tissue extracts derived from SSADH(-/-) mice. In vitro studies demonstrated the ability of 4,5-dihydroxyhexanoic acid to displace the GHB receptor ligand NCS-382 (IC(50) = 38 micromol/L), although not affecting GABA(B) receptor binding. Blood and urine derived from baboons administered with GHB also accumulated d-2-HG, but not 4,5-dihydroxyhexanoic acid. Our results indicate that d-2-HG is a prominent GHB metabolite and provide further evidence for the existence of d-2-hydroxyglutarate transhydrogenase in different mammalian species.

Endovascular model of rabbit hindlimb ischemia: a platform to evaluate therapeutic angiogenesis.

PURPOSE: Current animal hindlimb ischemia models involve surgical ligation of the femoral artery and delivery of therapeutic angiogenic agents into the adductor compartment. The authors hypothesize that an endovascular model of hindlimb ischemia would be a more appropriate platform, closely resembling atherosclerosis by occluding the vessel from within, causing less inflammation, wound healing and subsequent collateralization. MATERIALS AND METHODS: The left superficial femoral artery in 17 rabbits was occluded by endovascular coil embolization (n=9) or surgical ligation (n=8). Animals (n=3; in each group) were sacrificed on day 3 to determine the arteriolar luminal area, number of arterioles, microsphere determined perfusion, and degree of inflammation. On day 28, the remaining animals underwent calf blood pressure measurements and angiography to determine the number of collaterals and diameter of vessels supplying the hindlimb. RESULTS: Immediate postprocedure (day 0) and presacrifice (day 3 or 28) occlusion rates were 89% (eight of nine rabbits) and 100% for the endovascular model; 100% and 100% for the surgical model, respectively. Hindlimb paralysis and muscle atrophy was found in one surgical animal. On day 3, there was an increase in hindlimb perfusion (surgery, 0.04+/-0.01; endovascular, 0.02+/-0.01; P=.02), an increase in arteriolar luminal area (surgery, 481 microm+/-240; endovascular, 345 microm+/-151; P=.04), and a trend toward more inflammation (surgery, 5.5+/-3.8; endovascular, 2.5+/-3.0; P=.08) in the surgical group. There was no difference in number of vessels between both groups. On day 28 there was no difference in the calf blood pressure ratios or in the number of collaterals. However, there was enlargement of the distal profunda femoris artery, the vessel closest to the surgical incision, in the surgical group (L/R ratio: immediate post-occlusion, 1.06+/-0.11; day 28, 1.27+/-0.08; P=.02). CONCLUSION: The endovascular model was efficacious in providing occlusion of the superficial femoral artery, and induced less of an arteriogenic response compared with the surgical model. The authors believe that this endovascular model is a superior platform for studying therapeutic angiogenic agents.

Spontaneous and precipitated withdrawal after chronic intragastric administration of gamma-hydroxybutyrate (GHB) in baboons.

RATIONALE: gamma-Hydroxybuyrate (GHB) is a current drug of abuse that may produce physical dependence. OBJECTIVES: The present study characterized the behavioral effects of chronic GHB in baboons (n = 4), and evaluated whether signs of withdrawal occurred (1) after administration of the GABA-B antagonist CGP36742 during chronic GHB administration (precipitated withdrawal) and (2) following discontinuation of chronic GHB administration (spontaneous withdrawal). METHODS: Water (vehicle) and then GHB was continuously infused via intragastric (IG) catheters. GHB administration was initiated at 350 mg/kg per day, and the dose was increased by 100 mg/kg over 4 days to 750 mg/kg per day. Food pellets were available 20 h/day under a fixed ratio (FR5 or 10) schedule of reinforcement. Observation sessions and a 2-min fine motor task were conducted during vehicle and GHB administration. CGP36742 (32 and 56 mg/kg, IM) was administered during vehicle and chronic GHB administration. After a total of 32-36 days GHB administration was abruptly discontinued. Blood samples were collected during all interventions and analyzed for GHB content. RESULTS: Chronic GHB decreased food-maintained behavior, disrupted performance of the fine motor task, and produced ataxia, muscle relaxation, tremors and jerks. At the end of GHB administration, plasma levels of GHB ranged from 486 to 2080 micromol/L. Administration of CGP36742 during chronic GHB administration produced increases in aggression, self-directed behaviors, vomit/retch, tremors and/or jerks, which is consistent with a precipitated withdrawal syndrome. Similar signs were observed when GHB administration was discontinued. Seizures were not observed. CONCLUSIONS: These data indicate that chronic GHB administration produced physical dependence and that activation of the GABA-B receptor may be important for GHB physical dependence.

A new optional vena cava filter: retrieval at 12 weeks in an animal model.

PURPOSE: To test the feasibility and safety of percutaneous retrieval of a new inferior vena cava (IVC) filter, the Recovery Filter (RF), acutely and after 12-week implantation in sheep. MATERIALS AND METHODS: The RF is a bilevel filter with stabilizing arms and elastic hooks that allow retrieval with a unique retrieval cone after incorporation into the wall of the IVC. Twenty-four filters were placed in the infrarenal IVCs of 18 sheep. In six sheep, two filters were placed and then removed immediately; three sheep were killed acutely and three were killed after a healing period of 3 weeks. In 12 sheep, a single filter was placed and then removed 12 weeks later; six were killed after retrieval and six were killed after an 8-week healing period. RESULTS: The mean (+/-SD) transverse vena caval diameter was 15.3 mm +/- 2. All filters were deployed as intended and retrieved without difficulty. At sacrifice, there was no evidence of IVC perforation or retroperitoneal abnormality. The IVCs of the animals in the acute retrieval group showed minimal acute superficial injury that was largely reversed at 3 weeks. At 12 weeks, there was evidence of transmural incorporation of filter elements with narrowing of the IVCs. Solitary fibrotic abnormalities were present in the aorta adjacent to IVC lesions in nine of the 12 animals in the 12-week group. The IVC and aortic abnormalities were largely healed, with reversal of IVC narrowing after 8 weeks. CONCLUSION: The recovery filter can be reliably and safely retrieved acutely and 12 weeks after implantation in sheep.