Striatal dopamine in the response of brain and liver unsaturated and saturated free fatty acids following administration of C75 in CD-1 mice.

In order to clarify the mechanism of action of cerulenin analog, C75, known to suppress feeding behavior, food intake was measured in adult CD-1 male mice n=5 per group, treated i.p. with 10 and 20mg/kg of C75. Animals in both treatment groups had significantly lower 24h food consumption rate relative to the control group injected with vehicle. Striatal monoamine neurotransmitters and striatal as well as liver long chain free fatty acids concentrations were subsequently evaluated in another group treated i.p. with 20mg/kg C75. Acute exposure to C75 at 20mg/kg led to approximately 50% increase in the striatal dopamine levels and a decrease in dopamine turnover for up to 24h following the injection. The concentration of serotonin remained unchanged. Concentration of saturated fatty acids in the liver and striatum did not change, while striatal unsaturated myristoleic acid (cis-9-tetradecenoic acid) levels were significantly higher as early as 2h post-injection and remained elevated at 24h post-injection. These preliminary data suggest a central regulatory role of unsaturated fatty acids under dopaminergic control in the C75-induced anorexia. Pharmacological alterations in fatty acid metabolism may prove beneficial in the treatment of obesity.

Distribution of androstenedione and its effects on total free fatty acids in pregnant rats.

Androstenedione, an anabolic steroid used to enhance athletic performance, was administered in corn oil by gastric intubation once daily in the morning to nonpregnant female rats at a dose of 5 or 60 mg/kg/day, beginning two weeks before mating and continuing through gestation day (GD) 19. On GD 20, the distribution of androstenedione and other steroid metabolites was investigated in the maternal plasma and target organs, including brain and liver. The concentration of estradiol in plasma approached a statistically significant increase after treatment as compared with the controls, whereas the levels of androstenedione, testosterone and progesterone were not significantly different from the controls. In the liver, the concentrations of androstenedione and estradiol only were increased in a dose-related manner. None of these steroids was detectable in the brain. Androstenedione treatment also produced changes in the level of selected free fatty acids (FFAs) in the maternal blood, brain, liver and fetal brain. The concentrations of palmitic acid (16:0) and stearic acid (18:0) in the plasma were not significantly different between the controls and treated rats. However, oleic acid (18:1), linoleic acid (18:2) and docosahexaenoic acid (DHA, 22:6) were 17.94 +/- 2.06 microg/ml, 24.23 +/- 2.42 microg/ml and 4.08 +/- 0.53 microg/ml, respectively, in the controls, and none of these fatty acids was detectable in the treated plasma. On the other hand, palmitic, stearic, oleic, linoleic and DHA were present in both control and treated livers. Among the FFAs in liver, linoleic and DHA were increased 87% and 169%, respectively, over controls. Palmitic, stearic and oleic acids were not significantly affected by the 60 mg/kg treatment. These were present in both control maternal and fetal brains, whereas linoleic acid was found only in fetal brain control. DHA was present only in the control maternal brain (0.02 +/- 0.02 microg/mg protein) and fetal brain (0.24 +/- 0.15 microg/mg protein). The results indicated that androstenedione exhibits significantly different effects on the FFA composition among target organs during pregnancy.

Effects of oral androstenedione on phospholipid fatty acids, ATP, caspase-3, prostaglandin E(2) and C-reactive protein in serum and livers of pregnant and non-pregnant female rats.

Androstenedione, a steroidal dietary supplement taken to enhance athletic performance, could affect serum and liver lipid metabolism, induce liver toxicity or alter inflammatory response depending on dose and duration of exposure. Pregnancy could further exaggerate these effects. To examine this, mature female rats were gavaged with 0, 5, 30 or 60 mg/kg/day androstenedione beginning two weeks prior to mating and continuing through gestation day 19. Non-pregnant female rats were gavaged over the same time frame with 0 or 60 mg/kg/day androstenedione. Serum was collected and livers were removed from dams on gestation day 20 and from non-pregnant rats after 5 weeks of treatment. Androstenedione had no effect on serum total cholesterol, triglycerides or HDL-cholesterol, but significantly decreased C-reactive protein in pregnant rats and prostaglandin E(2) in serum of both pregnant and non-pregnant rats. There were treatment related decreases in liver ATP and, to a lesser degree, caspase-3 and no change in alkaline phosphatase of pregnant female rats. Androstenedione decreased docosahexaenoic acid in both serum and liver phospholipids of pregnant female rats. In conclusion, oral androstenedione did not result in overt hepatotoxicity in pregnant female rats, but produced modest changes in lipid metabolism and may impair regeneration of injured hepatic cells or tissue.

Effects of oral androstenedione on steroid metabolism in liver of pregnant and non-pregnant female rats.

It is unknown whether androstenedione, a steroidal dietary supplement taken to enhance athletic performance, can affect physiological hormone levels by altering liver enzyme activities that metabolize steroid hormones. Altered hormone levels could be especially devastating during pregnancy. Mature female rats were gavaged with 0, 5, 30 or 60 mg/kg/day androstenedione beginning two weeks prior to mating and continuing through gestation day 19. Non-pregnant female rats were gavaged over the same time frame with 0 or 60 mg/kg/day androstenedione. Livers were removed from dams on gestation day 20 and from non-pregnant rats after five weeks' treatment. Liver microsomes were incubated with 200 microM testosterone, and the reaction products were isolated and analyzed by HPLC. In pregnant rats, formation of 6alpha-, 15beta-, 7alpha-, 16beta-, and 2beta-hydroxytestosterone was increased significantly vs. control at the highest dose level only. Formation of 6beta-hydroxytestosterone increased significantly at both the 30 and 60 mg/kg/day dose levels. In non-pregnant rats, 60 mg/kg/day androstenedione significantly increased formation of 15beta-, 6beta-, 16beta-, and 2beta-hydroxytestosterone. The data suggest that high oral doses of androstenedione can induce some female rat liver cytochromes P450 that metabolize steroid hormones and that the response to androstenedione does not differ between pregnant and non-pregnant female rats.

Distribution of bisphenol A in the neuroendocrine organs of female rats.

The distribution of 14C-bisphenol A (BPA) in plasma and neuroendocrine organs was determined in Fischer 344 female rats following three oral doses (0.1, 10 or 100mg/kg). Plasma and tissue maximum concentrations (Cmax) were reached within 15-30 min of dosing. Plasma areas-under-the-curve (AUC) ranged from 0.06 to 53.9 microg-h/mL. The AUCs of the pituitary gland and uterus/gonads were 16-21% higher than that of plasma. The AUCs of hypothalamus and the rest of the brain were 43.7% and 77% of the plasma AUCs, respectively. In the brain tissue, the exposure increased linearly with the oral dose, as the dose was increased from 0.1 to 10 and 100 mg/kg; the exposure in the brain relative to the plasma increased by factors of 1, 1.19 and 1.24. This indicates that the brain barrier systems do not limit the access of the lipophilic BPA to the brain. The increases of the uterus/gonads relative to the plasma were 1, 1.07 and 1.04. Tissue partitioning was also examined in vitro by the uptake of 14C-BPA. The BPA tissue/blood partition coefficients were as follows: heart, 7.5; liver, 6.1; kidney, 6.4; fat, 3.6; muscle, 2.6; breast, 3.6; ovaries, 9.1; uterus, 5.9; stomach, 5.1; and small intestine, 6.7. The tissue/cerebrospinal fluid partition coefficients were as follows: pituitary gland, 12.8; brain stem, 6.1; cerebellum, 6.4; hippocampus, 7.1; hypothalamus, 6.1; frontal cortex, 4.9; and caudate nucleus, 6.8.

Effects of the seafood toxin domoic acid on glutamate uptake by rat astrocytes.

Pronounced glutamic acid uptake was observed after only 15 min with glutamate concentrations of 60 nmol/mg protein when astrocytes were incubated with 1 mM glutamic acid. The uptake increased with time to a steady-state glutamate level of above 160 nmol/mg protein by 45 min. The uptake was energy dependent. Reduced temperature (0 degrees C) and ouabain (100 microM) inhibited uptake by 86.7% (P<0.001; n=18) and 84.4% (P<0.001; n=18), respectively, when compared with controls. After exposure of astrocytes to glutamate (1 mM) in the incubation medium, in the presence of domoic acid (10 and 100 microM) at 5 and 60 min, domoic acid (10 microM) elevated glutamate uptake by 64.0% (P<0.05; n=34) at 5 min but decreased glutamate uptake by 47.8% (P<0.01; n=19) at 60 min compared with controls. A higher dose of domoic acid (100 microM) decreased glutamate uptake by 49.6% (P<0.01; n=20) and 61.3% (P<0.001; n=20) at 5 and 60 min, respectively, compared with controls. This study suggests that domoic acid may induce neurotoxicity because of the failure of astrocytes to remove extracellular glutamate. This may contribute to excitotoxic injury.

Distribution and excretion of radiolabelled tert-butylhydroquinone in Fischer 344 rats.

Uniformly 14C-ring-labelled tert-butylhydroquinone (TBHQ) was diluted with non-radioactive TBHQ and administered orally (for excretion studies) to Fischer 344 rats. An average of 72.9% and 10.6% of the administered radioactivity was recovered in the urine and faeces, respectively, of male rats, and 77.3% and 8.2% in the urine and faeces, respectively, of female rats in 4 days. No significant sex-related differences were found in either excretion, tissue distribution or urinary metabolites of TBHQ-derived radiolabel. For distribution studies, intraperitoneal doses were administered to female rats, and tissue levels of radiolabel were determined at various times after dosing. The parent compound quickly disappeared from tissue in vivo. The highest concentrations of radiolabel were found in the liver and kidneys. The urinary metabolites consisted of conjugated TBHQ and unidentified polar substance(s).

Quantitative low-dose assessment of seafood toxin, domoic acid, in the rat brain: application of physiologically-based pharmacokinetic (PBPK) modeling.

The purpose of this study was to construct a physiologically based pharmacokinetic model and demonstrate its ability to predict low-dose uptake of domoic acid, a seafood contaminant, in discrete areas of the rat brain. The model we used was derived from the generic PBPK model of our previous studies with 2,4-dichlorophenoxyacetic acid (Kim et al., 1994. Pharmacokinetic modeling of 2,4-dichlorophenoxyacetic acid (2,4-D) in rats and in rabbits brain following single dose administration. Toxicol. Lett. 74, 189; Kim et al., 1995. Development of a physiologically based pharmacokinetic model for 2,4-dichlorophenoxyacetic acid dosimetry in discrete areas of the rabbit brain. Neurotoxicol. Teratol. 17, 111), to which physiological- and chemical-specific parameters for domoic acid were applied. It incorporates two body compartments along with compartments for venous and arterial blood, cerebrospinal fluid, brain plasma and seven brain regions. Uptake of the blood-borne toxin is membrane-limited by the blood-brain barrier with clearance from the brain provided by cerebrospinal fluid `sink' mechanisms. This model generated predicted profiles of toxin level in brain and blood over a 1-h period that compared reasonably well with concentrations calculated from in vivo data of rats that had been given [(3)H]domoic acid intravenously (Preston and Hynie, 1991. Transfer constants for blood-brain barrier permeation of the neuroexcitatory shellfish toxin, domoic acid. Can. J. Neurol. Sci. 18, 39). This PBPK model should be an effective tool for evaluating the target doses that produce the potential neurotoxicity of domoic acid found in foods.

Kinetic analysis of glutamate transport by the miniswine choroid plexus in vitro.

Transport of glutamic acid by the choroid plexus, the blood-cerebrospinal fluid (CSF) barrier, was investigated by using the isolated choroid plexi from the fourth (FVCP) and lateral ventricles (LVCP) of the young adult miniswine in vitro. Glutamic acid uptake was very pronounced, with concentrations 7-fold (LVCP) and 2.4-fold (FVCP) higher in tissue than in medium after only 5 min of incubation with 1 microM glutamic acid. Tissue/medium ratios reached steady state by 15 min at 30-fold (LVCP) and 11-fold (FVCP). Uptake was energy-dependent and inhibited by ouabain and hypothermia. L-Aspartic acid was shown to be inhibitory in a concentration-dependent manner, suggesting that it shares a common transport system, whereas neither octanoic acid nor okadaic acid (transported by a separate fatty acid system) inhibited glutamic acid transport. At the same temperature, the labeled metabolite of glutamate (glutamine) in the tissue was 64.7%, 73.2%, and 72.5% of total radioactivity at 5, 30, and 60 min, respectively. The estimated Km values for glutamate uptake by the choroid plexus are 264 microM (FVCP) and 196 microM (LVCP); Vmax values are 87 (FVCP) and 147 (LVCP) nmol/g/min, respectively. These results indicate that, in addition to the metabolism of glutamate to glutamine, an active uptake mechanism is present in the choroid plexus of miniswine which may serve to regulate glutamic acid concentration in the CSF.