Reversal of tolerance to ethanol--a possible consequence of ethanol brain damage

Influence of long-term ethanol treatment on rat liver aniline and p-nitrophenol hydroxylation

The present study investigates the influence of long-term ethanol (EtOH) treatment of rats [10% (v/v) for 1, 4, 12, and 36 weeks] on hepatic microsomal cytochrome P450 (P450) content and liver aniline and p-nitrophenol hydroxylation. Total P450 per liver was stimulated after EtOH treatment for 1, 4, and 12 weeks. In the case of longer EtOH treatment no additional stimulation in P450 content was observed. Aniline and p-nitrophenol hydroxylase activity increased in direct relation with the duration of EtOH consumption. The stimulation of both enzymatic activities was different. In comparison to controls, in rats treated with 10% (v/v) EtOH for 1, 4, 12, and 36 weeks, an increase in nitrocatechol formation (1.1-, 1.2-, 2.2-, and 2.8-fold, respectively) was found. In contrast, no effect was observed on the metabolism of aniline after 1 and 4 weeks of EtOH consumption. Aniline hydroxylation increased after 12 and 36 weeks of EtOH treatment only. Addition of EtOH in vitro had an inhibitory effect on both aniline and p-nitrophenol hydroxylation. With liver microsomes from controls as well as EtOH-treated rats the inhibition of p-nitrophenol hydroxylation was competitive in nature (Ki = 5.6 mM and Ki = 5.9 mM). In contrast, there was a competitive inhibition of aniline hydroxylation with liver microsomes from controls only. With microsomes from EtOH-treated rats a mixed inhibition was found.

Effect of NMDA antagonists on rapid and chronic tolerance to ethanol: importance of intoxicated practice

Recent studies from our laboratory have shown that NMDA antagonists ((+)MK-801 and ketamine) inhibit the development of both rapid and chronic tolerance to the motor-impairing (moving belt test) and hypothermic effects of ethanol. The present experiments were designed to determine a) the generality of this inhibition, by using a different test of motor function, the tilt-plane test, and b) the possible importance of the experimental paradigm (i.e., with and without intoxicated practice), for the effect of the NMDA antagonist on ethanol tolerance. Daily administration of ethanol 3.3 g/kg for 5 days produced the same degree of tolerance on this test, whether it was given as a single dose of 3.3 g/kg before the daily training session or as divided doses of 2.3 g/kg before and 1 g/kg immediately after the session. The inhibitory effect of a single dose of (+)MK-801 (0.25 mg/kg IP) on rapid tolerance did not last longer than 1 day. Therefore, daily administration of the NMDA antagonists was necessary to block development of chronic tolerance. Daily injection of (+)MK-801 (0.25 mg/kg IP) failed to block chronic tolerance, but inclusion of a second dose of (+)MK-801 daily, and progressive increase of this second dose during the chronic treatment period did block chronic tolerance. Unlike (+)MK-801, ketamine does not have motor-impairing effects of its own, and does not potentiate those of ethanol; it was, therefore, used in the remaining experiments. Groups of rats received ethanol (3.3 g/kg) or saline, either before a daily practice session on the tilt-plane or after it.(ABSTRACT TRUNCATED AT 250 WORDS)

Factors regulating ethanol tolerance

Ethanol tolerance is a complex phenomenon. Its development is governed by pharmacological and behavioural, as well as genetic factors. The doses of ethanol employed and the duration of ethanol treatment are important pharmacological variables. Behavioural factors such as experience of intoxication and Pavlovian conditioning may also affect the development or manifestation of ethanol tolerance. Genetic factors can influence the development of tolerance directly or/and indirectly through its influence on the initial sensitivity to ethanol. The relevance and implication of tolerance, particularly conditioned tolerance in alcohol abuse and alcoholism, are discussed.

[Occurrence of the alcoholic tolerance phenomenon and its relation to the daily frequency of ethanol doses and with the presence of a withdrawal interval, in an experimental model of alcoholism in rats]

In this paper we present the effects of the number of daily toxic doses of alcohol and of the duration of withdrawal period on alcohol tolerance in rats submitted to cycles of 21 doses each. It was observed that alcohol tolerance was increased in animals which received less number of alcohol doses by day and that some degree of tolerance can be detected even after a withdrawal interval of 15 days.

Biochemical basis of alcoholism: statements and hypotheses of present research

Experimental results and theoretical considerations on the biology of alcoholism are devoted to the following topics: genetically determined differences in metabolic tolerance; participation of the alternative alcohol metabolizing systems in chronic alcohol intake; genetically determined differences in functional tolerance of the CNS to the hypnotic effect of alcohol; cross tolerance between alcohol and centrally active drugs; dissociation of tolerance and cross tolerance from physical dependence; permanent effect of uncontrolled drinking behavior induced by alkaloid metabolites in the CNS; genetically determined alterations in the function of opiate receptors; and genetic predisposition to addiction due to innate endorphin deficiency. For the purpose of introducing the most important research teams and their main work, statements from selected publications of individual groups have been classified as to subject matter and summarized. Although the number for summary-quotations had to be restricted, the criterion for selection was the relevance to the etiology of alcoholism rather than consequences of alcohol drinking.

Effects of ethanol on thermoregulation

Clinical reports of accidental hypothermia in alcohol intoxicated individuals exposed to low ambient temperature ( Paton , 1983) have generally been borne out by experimental studies in healthy volunteers. Small doses of ethanol, given to human subjects at normal ambient temperature (Ta), have very little effect on body temperature but a combination of large dose, low Ta and vasodilatation provoked by strenuous exercise, causes a sharp fall in rectal temperature. In experimental animals, the use of relatively larger doses of alcohol and more extreme temperatures, both above and below the thermoneutral zone, has shown that the effect of ethanol is essentially poikilothermic, i.e. an impairment of adaptation to both heat and cold. This effect has been studied in greater detail, in relation to each of the basic thermoregulatory processes. Though small doses of alcohol may increase the metabolic rate under some circumstances, the most common effect at low Ta is inhibition of shivering and therefore reduction of thermogenesis. At the same time it tends to cause increased heat loss by cutaneous vasodilatation. This makes for a greater feeling of comfort in the cold exposed subjects but increases in rate of fall of core temperature. The combination of decreased thermogenesis and increased heat loss, despite falling body temperature, is suggestive of a lowering of the set-point of the thermoregulatory control mechanisms. Consistent with this is a slight increase in ventilatory heat loss after low doses of ethanol but larger doses cause respiratory depression, so that heat loss through the lungs is minor. However, at high Ta ethanol caused hyperthermia in experimental animals and shows enhanced lethality, so that impairment of thermoregulatory effector mechanisms seems to be at least as important as change in set-point. Studies of the effects of ethanol on electrophysiological activity of single neurons in the pre-optic area and anterior hypothalamus (POAH), biochemical activities of neuronal membranes, hypothalamic blood flow, conventional neurotransmitters, amino acid putative neurotransmitters, neuropeptides, prostaglandins and inorganic ions have all failed so far to yield a clear comprehensive picture of the mechanisms by which ethanol affects thermoregulation. In each case, contradictory evidence has been obtained concerning the consequences of ethanol administration, whether by oral, intraperitoneal, intravenous, intracerebroventricular, or direct local (POAH) route.(ABSTRACT TRUNCATED AT 400 WORDS)