Barbiturates induce mitochondrial depolarization and potentiate excitotoxic neuronal death.

Barbiturates are widely used as anesthetics, anticonvulsants, and neuroprotective agents. However, barbiturates may also inhibit mitochondrial respiration, and mitochondrial inhibitors are known to potentiate NMDA receptor-mediated neurotoxicity. Here we used rat cortical cultures to examine the effect of barbiturates on neuronal mitochondria and responses to NMDA receptor stimulation. The barbiturates tested, secobarbital, amobarbital, and thiamylal, each potentiated NMDA-induced neuron death at barbiturate concentrations relevant to clinical and experimental use (100-300 microm). By using rhodamine-123 under quenching conditions, barbiturates in this concentration range were shown to depolarize neuronal mitochondria and greatly amplify NMDA-induced mitochondrial depolarization. Barbiturate-induced mitochondrial depolarization was increased by the ATP synthase inhibitor oligomycin, indicating that barbiturates act by inhibiting electron transport sufficiently to cause ATP synthase reversal. Barbiturates similarly amplified the effects of NMDA on cytoplasmic free calcium concentrations. The cell-impermeant barbiturate N-glucoside amobarbital did not influence mitochondrial potential or potentiate NMDA neurotoxicity or calcium responses. However, all of the barbiturates attenuated NMDA-induced calcium elevations and cell death when present at millimolar concentrations. Whole-cell patch-clamp studies showed that these effects may be attributable to actions at the cell membrane, resulting in a block of NMDA-induced current flux at millimolar barbiturate concentrations. Together, these findings reconcile previous reports of opposing effects on barbiturates on NMDA neurotoxicity and show that barbiturate effects on neuronal mitochondria can be functionally significant. Effects of barbiturates on neuronal mitochondria should be considered in experimental and clinical application of these drugs.

HPLC analysis for amobarbital N-glycosides in urine.

A study was undertaken to determine if humans excrete both amobarbital N-glucuronides and N-glucosides in urine after an oral dose of amobarbital. Amobarbital N-glucuronides were synthesized and characterized. A reverse phase LC method using post-column pH adjustment and UV detection at 240 nm was developed and used for the quantification of the amobarbital N-glucosides and N-glucuronides in human urine. Amobarbital was administered orally to seven male subjects and the total urine was collected for a period of 48-53 h after dosing. After filtration, the urine was injected directly onto the HPLC column to analyze for the presence of metabolites. The previously identified (5S)-amobarbital N-glucoside was detected in all seven subjects. The (5R)-amobarbital N-glucoside was detected at lower concentrations in only four of the subjects. At the levels at which amobarbital N-glucosides were detected, there was no evidence for the formation and excretion of the amobarbital N-glucuronides. Amobarbital N-glucuronidation is not a quantitatively significant pathway for the biodisposition of amobarbital in humans.

[Synthesis, structure elucidation and biological activity of thio- analogs of drugs with the examples of chlorthenoxazine and amobarbital]. / Synthese, Strukturaufklärung und biologische Wirksamkeitsprüfung thioanaloger Arzneistoffe am Beispiel des Chlorthenoxazins und Amobarbitals.

Two drugs (chlorthenoxazine, amobarbital) were converted into their S-analogues derivatives via thiation with the P4S10-pyridine complex. The identity of structure isomers was confirmed by 13C NMR. A preliminary evaluation for their biological activities revealed that trithioamobarbital exhibits some notable spasmolytic effects. The substitution of oxygen by sulphur in chlorthenoxazine resulted in a complete loss of antiinflammatory activity.

A method for studying drug metabolism in populations: racial differences in amobarbital metabolism.

The two main metabolites of amobarbital excreted in urine are 3'-hydroxyamobarbital (C-OH) and 1-(beta-D-glucopyranosyl) amobarbital (N-glu). When testing the metabolite ratio in small single samples of urine, it was found that the urine in a Caucasian population contained about one-third glucose conjugation and two-thirds hydroxylation product, while an Oriental population excreted both metabolites in equal proportion. Attempts to learn the causes for the different metabolite ratios led to an investigation of metabolite concentrations in urine. The sums of the average urinary concentration of C-OH was greater in Caucasians than in Orientals, no matter how the data were expressed; the reverse was true for the N-glu metabolite. C-OH data was scattered more widely among Orientals than Caucasians; this might indicate bimodality of the distribution curves. There also was a trend toward more N-glu metabolite in urine of females than of males. Measuring the metabolite/creatinine ratios narrowed the distribution range of the data, particularly after correction for sex difference in creatinine, but population differences were not changed. Expected relationships between metabolite content of urine, sampling times, and plasma half-life (t1/2) were established by calculation. A Caucasian female with no capacity for N-glucosidation was found during the first part of this population survey. An Oriental male with only trace capacity for amobarbital hydroxylation was found in the second part.