The role of ethanol in diluents of drugs that protect mice from hypoxia

Ethanol alters the expression of ion channel genes in Daphnia pulex

BACKGROUND

Heavy drinking can increase heart rate and blood glucose, induce hypoxic tolerance, impair brain cognitive functions, and alter gene expressions. These phenomena may occur even in response to small dose of ethanol exposure or during its withdrawal.

OBJECTIVES

To evaluate whether persistent low concentrations of ethanol exposure affect organism function and the gene expressions of ion channels.

METHODS

Daphnids were randomized to receive placebo 300 min, 2 mM ethanol 300 min, or 2 mM ethanol 240 min and then placebo 60 min. Heart rate, glucose levels, phototactic behavior, and hypoxic tolerance were recorded during experiment. At the end of the study, changes in the mRNA levels of ion channel genes were assessed in response to exposure to ethanol using quantitative polymerase chain reaction (PCR) techniques.

RESULTS

Heart rate was reversibly increased by ethanol withdrawal and returned to basal levels upon re-exposure to ethanol. Fifteen of 120 ion channel transcripts were affected by persistent ethanol exposure. Neither ethanol withdrawal nor persistent exposures showed an effect on blood glucose, phototactic behavior, or hypoxic tolerance.

CONCLUSIONS

Small doses of ethanol can increase heart rate and alter gene expression of multiple ion channels in Daphnia pulex. Affected ion channel genes may assist in understanding the mechanism of ethanol adaptation and tolerance.

Strain differences in response to acute hypoxia: CD-1 versus C57BL/6J mice

Some mammals respond to hypoxia by lowering metabolic demand for oxygen and others by maximizing efficiency of oxygen usage: the former strategy is generally held to be the more effective. We describe within the same species one outbred strain (CD-1) that lowers demand and another inbred strain (C57BL/6J) that maximizes oxygen efficiency to markedly extend hypoxic tolerance. Unanesthetized adult male mice ( Mus musculus, CD-1 and C57BL/6J) between 20 and 35 g were used. Sham-conditioned (SC) C57BL/6J mice survived severe hypoxia (4.5% O2, balance N2) roughly twice as long as SC CD-1 mice (median 211 and 93.5 s, respectively; P < 0.0001). Following acute hypoxic conditioning (HC), C57BL/6J mice survived subsequent hypoxia 10 times longer than HC CD-1 mice (median 2,198 and 238 s respectively; P < 0.0001). Therefore, C57BL/6J mice are both naturally more tolerant to hypoxia and show a greater increase in hypoxic tolerance in response to hypoxic conditioning. Indirect calorimetry indicates that CD-1 mice lower mass-specific oxygen consumption (V̇′o2 in ml O2·kg−1·min−1) and carbon dioxide production (V̇′co2 in ml CO2·kg−1·min−1) in response to HC ( P = 0.002 and P < 0.0001, respectively), but C57BL/6J mice maintain V̇′o2 and V̇′co2 after HC. Respiratory exchange ratio and fluorometric assay of plasma ketones suggest that C57BL/6J mice rapidly switch to ketone metabolism, a more efficient substrate, while CD-1 mice reduce overall metabolic activity. We conclude that under severe hypoxia in mice, switching fuel, possibly to ketones, while maintaining V̇′o2, may confer a greater survival advantage than simply lowering demand.

Acute protective effect of nimodipine and dimethyl sulfoxide against hypoxic and ischemic damage in brain slices

Nimodipine and dimethyl sulfoxide (DMSO) were tested (alone and in combination) regarding their ability to increase hypoxic tolerance of brain slices under 'hypoxic' (deprivation of oxygen) or 'ischemic' (hypoxia+withdrawal of glucose) conditions. Direct current (DC) and evoked potentials were recorded in the CA1 region of hippocampal slices of adult guinea pigs. After induction of hypoxia or ischemia, the latency of anoxic terminal negativity (ATN) of the DC potential was determined during superfusion with artificial cerebrospinal fluid alone (aCSF), and during superfusion with aCSF containing DMSO [0.1% (14.1 mmol/l) and 0.4% (56.3 mmol/l)] with the addition of nimodipine (40 micromol/l). Latencies of ATN with first hypoxia were 6.7+/-3.7 min in the control group, 9. 3+/-4.2 min in the 0.4% DMSO group and 12.3+/-5.5 min (P=0.007) in the nimodipine/0.4% DMSO group. Latencies of ATN with first ischemia were 2.9+/-2 min in the control group, 4.1+/-1.6 min in the 0.1% DMSO group, 7.1+/-3.9 min in the 0.4% DMSO group (P=0.006), 5.3+/-1. 5 min in the nimodipine/0.1% DMSO group and 7.6+/-3 min (P<0.001) in the nimodipine/0.4% DMSO group. DMSO (0.4%), either alone or in combination with nimodipine, increase the latency of the ATN after acute onset of hypoxia and ischemia.

Role of endogenous opioid peptides in the acute adaptation to hypoxia

A non-lethal, hypoxic conditioning stimulus has been shown by Rising and D'Alecy to increase hypoxic survival time in mice. To determine if endogenous opioids alter the hypoxic conditioning-induced increase in hypoxic survival time, we administered naloxone (0.1, 1.0 mg/kg i.p.) or saline (0.3 ml i.p.) 5 min prior to conditioning. Sixty percent of the mice received the hypoxic conditioning stimulus consisting of three sequential hypoxic exposures (4.5% oxygen balance nitrogen for 1.5, 2 and 2.5 min) separated by 5 min of room air. The remaining mice did not receive hypoxic conditioning but instead remained in room air for this time. All mice were tested for hypoxic survival by first exposing them to 20 s of 8.5% oxygen balance nitrogen followed by exposure to 4.5% oxygen balance nitrogen. The hypoxic survival time was recorded as the time from the onset of the 4.5% oxygen to the cessation of spontaneous ventilation. Naloxone (1 mg/kg) completely blocked the adaptation to hypoxia induced by hypoxic conditioning (P = 0.003). Morphine (1, 5, 10 and 20 mg/kg) had no effect on hypoxic adaptation; however, 50 mg/kg morphine decreased the adaptation induced by conditioning (P less than 0.0001) possibly due to high dose toxicity. These data suggest that endogenous opioids are involved in the protective adaptation to hypoxia induced by prior exposure to non-lethal hypoxia.

Nimodipine decreases resuscitability in a cardiopulmonary arrest model in the rat

Although calcium has been implicated in ischemia-induced brain death or dysfunction, many animal studies do not show a beneficial effect of calcium-entry blockers given after resuscitation from a cardiopulmonary arrest (CPA). This may be due to the fact that treatment was started too late; we, therefore, evaluated the effect of the calcium-entry blocker nimodipine administered at the earliest feasible postischemic moment, i.e. at the start of the resuscitation attempts. In anesthetized Wistar rats, CPA was induced by an intra-cardiac injection of KCl, and maintained for 7 min by chest restriction. At the start of the resuscitation attempts, 50 rats were blindly and randomly assigned to intravenous treatment with either nimodipine (10 micrograms/kg over 2 min, followed by 1 micrograms/kg per min for 60 min; n = 25) or saline (n = 25). In the nimodipine group, significantly less rats could be resuscitated (11/25 versus 20/25) and the survival rate at the end of the 7 days evaluation period tended to be lower (5/25 versus 11/25). In the rats surviving after 7 days, there was no difference between both groups in incidence of seizures, neurological status and histological lesions in the hippocampus. It is concluded that nimodipine, in the dose tested and given during resuscitation in this rat model, has a detrimental effect on resuscitability and no beneficial effect on the neurological outcome in the surviving animals.

Effects of ethanol in acute carbon monoxide poisoning

The combined effects of ethyl alcohol (ETOH) intoxication and carbon monoxide (CO) poisoning were studied in the Levine-prepared rat. Infusion or injection of ETOH before and during 90 min of CO exposure to blood levels 2-4 times those considered legally drunk in humans, increased survival at 2400 ppm, and extended the tolerance time at 2400 ppm and 3000 ppm. CO exposure produced the usual hypothermia, hypotension and hemoconcentration; these responses were not altered by concurrent ETOH treatment. Blood ETOH concentration was increased in the presence of CO, and this was related to CO concentration. Although ETOH did not alter the average degree of hypoglycemia seen during the later stages of CO exposure, rats with the highest ETOH concentration tended to have the lowest blood glucose. ETOH increased the magnitude of the hyperglycemic rebound during recovery from exposure to both CO concentrations. Moreover, the magnitude of the recovery hyperglycemic rebound was directly related to the magnitude of the previous hypoglycemia, at both CO concentrations, with or without ETOH. Rats dying during exposure to both CO concentrations were severely hypoglycemic, whereas survivors maintained more or less normal blood glucose concentrations. The results suggest that the presence of ETOH during CO poisoning increases blood ETOH to higher than expected levels and provides a significant degree of survival protection.

Long-term neurological assessment of the post-resuscitative effects of flunarizine, verapamil and nimodipine in a new model of global complete ischaemia

In anesthetized rats, global complete ischaemia lasting for 9 min was induced by controlled hydraulic compression of the chest. A neurological score, based on cranial and spinal reflexes, postural tone, gait, movement and limb placement, was determined at 2 hr and 1, 2, 3, 7, 14, 21 and 28 days after resuscitation. Three doses of three calcium antagonists, flunarizine, verapamil and nimodipine and their respective solvents, were given intravenously during the resuscitation. The total neurological score was significantly better than solvent with 0.16 and 0.63 mg/kg of flunarizine and 0.04 and 0.16 mg/kg of verapamil; it was significantly better with solvent (10% ethanol) than with 0.04 and 0.16 mg/kg of nimodipine. The deficiency in tactile placing reactions of the hindpaws was the most resistant to therapy. This non-invasive model of global ischaemia in rats seems useful for the evaluation of drugs, since it requires minimal anesthesia and allows assessment of neurological recovery over an extended period of time.

Failure of nimodipine to reverse acute experimental spinal cord injury

The calcium-channel blocking agent, nimodipine, was administered to cats for 5 days after acute experimental SCI. Six weeks after injury, no significant differences in neurologic recovery or white matter tissue preservation at the injury site were found between treated and control animals.