[Effects of oxiracetam on the decrease in population spikes in hypoxic and low glucose media].

Evoked potentials were recorded in rat cerebral cortical slices. The amplitude of the evoked potential was reduced by perfusion with hypoxic (0-25%) or low glucose (0-5 mM) media in a concentration-dependent manner, and the evoked potentials disappeared under severe conditions (below 15% O2, below 3 mM glucose). We investigated the protective effects of oxiracetam on the decrease in evoked potentials under hypoxic (15% O2) and low glucose (3 mM glucose) conditions. Drugs were perfused from 45 min before hypoxic or low glucose perfusion to the end of the experiment. Oxiracetam (10(-6)-10(-5) M) dose-dependently minimized the amplitude reduction of evoked potentials and prolonged their disappearance time. At a concentration of 10(-5) M, oxiracetam protected against the disappearance of evoked potential in 5 of the 6 samples under hypoxic conditions and in all 6 samples under low glucose conditions. Indeloxazine (5 x 10(-6)-10(-5) M) and bifemelane (5 x 10(-6)-10(-5) M) prevented the reduction of the amplitude of evoked potentials under low glucose conditions. However, these drugs had no effect at a concentration of 10(-6) M. These data indicate that oxiracetam has a protective effect against neuronal dysfunction and that this effect develops at a lower concentration than those of indeloxazine and bifemelane.

The effects of oxiracetam (CT-848) on local cerebral glucose utilization after focal cerebral ischemia in rats.

The effects of oxiracetam on the reduction of brain metabolism induced by focal cerebral ischemia were investigated by measuring local cerebral glucose utilization (LCGU) in rats 24 hr after left middle cerebral artery occlusion. Focal cerebral ischemia reduced LCGU in the entire ipsilateral cortex, the greatest reduction being in the lateral parts of the frontoparietal cortex. LCGU was slightly reduced in the contralateral cortex; this reduction was considered to be caused by diaschisis. Oxiracetam was administered intraperitoneally for 3 days prior to middle cerebral artery occlusion. In the ipsilateral cortex, LCGU reduction was minimized in the ischemic center areas by oxiracetam at a dose of 400 mg/kg and in more extensive areas, by a dose of 800 mg/kg. Moreover, oxiracetam at a dose of 800 mg/kg enhanced metabolism impaired by diaschisis in the caudal areas of the contralateral cortex. These findings suggest that oxiracetam minimizes the reduction of brain function induced by ischemia and may therefore be useful in the treatment of cerebrovascular disease.

Antihypertensive effects of nisoldipine and reference drugs in certain types of hypertensive rats.

The hypotensive effects of nisoldipine (Bay K 5552), compared with those of nifedipine, nicardipine and hydralazine, in normotensive rats (NR), spontaneously hypertensive rats (SHR), DOCA-NaCl hypertensive rats (DNR) and renal hypertensive rats (RHR), were studied. The changes in plasma renin activity (PRA) after treatment with nisoldipine and these reference drugs were also studied. The results of this study revealed that: 1. Nisoldipine caused more potent antihypertensive effects in SHR, DNR and RHR than in NR. 2. The antihypertensive effects of nisoldipine in SHR were almost equipotent to those of nifedipine, nicardipine and hydralazine. However, in NR, DNR and RHR, the effects of nisoldipine were weaker than those of the reference drugs. 3. The positive chronotropic effects of nisoldipine were less remarkable than those elicited by nifedipine, nicardipine and hydralazine in all types of hypertensive rats, except SHR. 4. As did nifedipine and nicardipine, nisoldipine caused an increase of the plasma renin activity in NR and SHR, though its potency was weaker than those of nifedipine and nicardipine.

[The neuromuscular blocking activity of isepamicin sulfate (HAPA-B) compared with other aminoglycoside antibiotics].

Effects of isepamicin sulfate (HAPA-B), a new aminoglycoside antibiotic, on the neuromuscular transmission were studied in rats and compared with those of amikacin (AMK) or other aminoglycoside antibiotics. The HAPA-B, as well as other aminoglycoside antibiotics, depressed the twitch response of diaphragm to phrenic nerve stimulation in vitro. The depression effects of different drugs were compared and graded in the order of strengths of blocking action as: netilmicin (NTL) greater than gentamicin (GM) greater than streptomycin (SM) greater than kanamycin (KM) greater than AMK greater than HAPA-B. The IC50 (concentration which inhibited the response by 50%) of HAPA-B was 3.6 X 10(-3) g/ml. The neuromuscular blockade produced by HAPA-B was reversed by CaCl2, KCl or caffeine but not by neostigmine. D-Tubocurarine or MgCl2 augmented the neuromuscular effects of HAPA-B. Intramuscular (400 mg/kg) and intravenous (100 mg/kg) injections of HAPA-B did not affect the twitch response of gastrocnemius muscle to sciatic nerve stimulation in situ. Intravenous injection of 200 mg/kg caused death in some rats and depression of the twitch response in others. Intravenous AMK produced no significant effect on the twitch response at 50 mg/kg and caused death at 100 mg/kg. GM and SM caused death or significant degree of depression of the twitch response at intravenous doses of 50 mg/kg. In experiments of intravenous drug infusion for 60 minutes, the twitch response was depressed by HAPA-B at 400 mg/kg/hr and by AMK at 200 and 400 mg/kg/hr. In conclusion, HAPA-B has a neuromuscular blocking action presumably at the nerve terminal. However, its action was the weakest among the aminoglycoside antibiotics tested.

Comparative study of various H1-blockers on neuropharmacological and behavioral effects including 1-(2-ethoxyethyl)-2-(4-methyl-1-homopiperazinyl)benzimidazole difumarate (KB-2413), a new antiallergic agent.

In a conditioned avoidance response tested in rats, all of the H1-blockers employed caused a dose-related inhibition at doses 5-20 mg/kg (i.v.) except for ketotifen that elicited significant suppression even at a dose of 1 mg/kg. No inhibition was seen after administration of 1-(2-ethoxyethyl)-2-(4-methyl-1-homopiperazinyl)benzimidazole difumarate (KB-2413). ED50s were ranged from 4.1 to 7.4 mg/kg in diphenhydramine, pyrilamine and promethazine. In laminectomized rats, diphenhydramine, pyrilamine, promethazine and ketotifen suppressed the amplitudes of monosynaptic reflex potentials at doses higher than 2 mg/kg (i.v.). In the case of chlorpheniramine, significant inhibition was observed at a dose of 20 mg/kg. In a polysynaptic reflex, similar but less prominent inhibitions were affected by those drugs. However, KB-2413 did not influence spinal reflexes even at a dose of 20 mg/kg. In the rat phrenic nerve-diaphragm preparation, perfusion of H1-blockers at a concentration of 10(-5) M decreased the amplitudes of end-plate potentials except for chlorpheniramine and KB-2413. At 10(-4) M, all the test drugs caused significant inhibition. When the action potential of superior cervical ganglion was measured by the sucrose gap method, promethazine inhibited the action potential significantly at 10(-6) M, but the rest of the test drugs depressed the potentials at 10(-5) M. In spontaneous EEG, all H1-blockers caused a marked drowsy pattern at lower doses (2-5 mg/kg) except for chlorpheniramine, while in higher doses (10-20 mg/kg) epileptic signs in EEG with or without convulsive behavior were noticed. However, after KB-2413 (5-20 mg/kg) neither drowsy nor seizure pattern was observed, in EEG or behavior.