Post-ischaemic treatment with orotic acid prevents neuronal injury in gerbil brain ischaemia

Effects of nucleotides on learning and memory in a Morris water maze test in normal and basal forebrain-lesioned rats

The effects of nucleotides on learning and memory were studied in normal and basal forebrain-lesioned rats using a Morris water maze test. Chronic oral administration of a nucleotide mixture (500 mg/kg), containing an equal weight of the disodium salts of adenosine 5'-monophosphate, guanosine 5'-monophosphate, inosine 5'-monophosphate, cytidine 5'-monophosphate, and uridine 5'-monophosphate facilitated learning acquisition in normal rats. In basal forebrain-lesioned rats, administration of the nucleotide mixture showed a tendency to improve learning acquisition and memory retrieval. In the biochemical studies, no significant changes were observed in brain choline and acetylcholine levels by treatment with the nucleotide mixture at the doses tested in both normal and basal forebrain-lesioned rats. The nucleotides did not affect the monoaminergic systems in normal rats, but did cause some changes in these systems in basal forebrain-lesioned rats. The present studies indicate that nucleotides ameliorate learning and memory processes in normal rats, but not in basal forebrain-lesioned rats, and they also modulate the activity of the central monoaminergic systems under certain conditions.

Tolbutamide attenuates diazoxide-induced aggravation of hypoxic cell injury

ATP-dependent potassium (KATP) channels of neurons are closed in the presence of physiological levels of intracellular ATP and open when ATP is depleted during hypoxia or metabolic damage. The present study investigates hypoxic alterations of purine and pyrimidine nucleotide levels supposed to intracellularly modulate KATP channels. In addition, the effects of the KATP channel activator diazoxide and its antagonist tolbutamide were investigated on ATP, GTP, CTP and UTP levels in slices of the parietal cortex. Hypoxia was evoked by saturation of the medium with 95% N2-5% CO2 instead of 95% O2-5% CO2 for 5 min. Nucleotide contents were measured by anion-exchange HPLC in neutralized perchloric acid extracts obtained from slices frozen immediately at the end of incubation. Hypoxia per se decreased purine and pyrimidine nucleoside triphosphate contents. Thus, ATP and GTP contents were reduced to 69.9 and 77.6% of the respective normoxic levels. UTP and CTP contents were even more decreased (to 60.9 and 41.6%),, probably because the salvage pathway of these pyrimidine nucleotides is less effective than that of the purine nucleotides ATP and GTP. While tolbutamide (30 microM) had no effect on the hypoxia-induced decrease of nucleotides, diazoxide at 300, but not 30 microM aggravated the decline of ATP, UTP and CTP to 51.8, 37.5 and 28.5% of the contents observed at normoxia; GTP levels also showed a tendency to decrease after diazoxide application. Tolbutamide (300 microM) antagonized the effects of diazoxide (300 but not 30 microM aggravated the decline of ATP, UTP and CTP to 51.8, 37.5 and 28.5% of the contents observed at normoxia; GTP levels also showed a tendency to decrease after diazoxide application. Tolbutamide (300 microM) antagonized the effects of diazoxide (300 MicroM). Nucleoside diphosphate (ADP, GDP and UDP) levels were uniformly increased by hypoxia. There was no hypoxia-induced increase of ADP contents in the presence of tolbutamide (300 microM). The ATP/ADP, GTP/GDP and UTP/UDP ratios uniformly declined at a low pO2. However, only the ATP/ADP ratio was decreased further by diazoxide (300 microM). The observed alterations in nucleotide contents may be of importance for long- and short-term processes related to acute cerebral hypoxia. Thus, hypoxia-induced alterations of purine and pyrimidine nucleotide levels may influence the open state of KATP-channels during the period of reversible hypoxic cerebral injury. Furthermore, alterations during the irreversible period of cerebral injury may also arise, as a consequence of decreased pyrimidine nucleotide contents affecting cell survival viaprotein and DNA synthesis.

Neuroprotective effect of YM-39558 in focal cerebral ischemia in cats

We studied the effect of YM-39558, orotic acid ethylester, in a focal cerebral ischemia model in anesthetized cats. YM-39558 has good permeability across the blood brain barrier, and in the brain is hydrolyzed to orotic acid, the main active substance. Cats were subjected to permanent occlusion of the middle cerebral artery (MCA) for 6 h, then killed and examined histologically. Treatment with YM-39558 (intravenous infusion of 11.8 mg (10 mg as orotic acid)/6 ml per kg per h) starting 15 min after MCA occlusion markedly reduced the volume of ischemic damage (from 2450 +/- 82 mm3 of the cerebral hemisphere in the saline-treated cats to 1644 +/- 123 mm3 in the YM-39558-treated cats, P < 0.01). In contrast, YM-39558 (2.26 and 1.18 mg/0.8 ml per kg per h) showed no significant protective effect on ischemic damage. No significant differences were observed between saline- and YM-39558-treated cats concerning physiological variables including brain temperature. This evidence for the neuroprotective efficacy of YM-39558 in gyrencephalic species suggests its therapeutic potential in the treatment of stroke in humans.

Neuroprotective effect of YM-39558, orotic acid ethylester, in gerbil forebrain ischemia

We studied the effects of orotic acid and YM-39558 (2,6-dioxo-1,2,3,6-tetrahydropyrimidine-4-carboxylic acid ethyl ester), orotic acid ethylester, on delayed neuronal death of hippocampal CA1 neurons induced by transient forebrain ischemia. Our data indicated that YM-39558 had high permeability across the blood brain barrier and was hydrolyzed to orotic acid, the active substance, in the brain. The neuronal damage was reduced significantly in animals intraperitoneally treated with YM-39558 (100 mg/kg x 3) after ischemia, but not with orotic acid in the same way. The results also suggested that the maintenance of a few ten micromolar orotic acid in cerebrospinal fluid were needed for its neuroprotective effects.