Alcohol is thought to be the earliest drug in common use, probably dating back to the paleolithic age (around 8,000 bc). Initially, alcoholic drinks were obtained through yeast-induced conversion of sugars (fermentation) from a variety of carbohydrate-based liquids, such as honey and grains steeped in water or fruit/vegetable juices. Fermentation-obtained beverages have a maximum alcohol content of about 12%, since alcohol concentration above that level causes the yeast to die, thus preventing further fermentation. Around 800 ad, Arabs discovered a process of distillation of fermented liquids, which produces beverages of much higher alcohol content, sometimes as high as 80%. The use of both types of alcoholic beverages - fermented drinks such as beer, wine, or mead and distilled drinks ("spirits"), such as whiskey, vodka, or gin - is widely spread throughout the history as well as in modern times, and it plays a significant role in social and religious customs of many cultures.
Alcohol exerts a number of effects, ranging from stimulant and pleasurable to sedative, anxiolytic, attention reduction, amnestic, anticonvulsant, muscle relaxant, hypnotic anesthetic, and can lead to death. The effects of alcohol are biphasic: at low blood alcohol concentrations (BAC) it is disinhibitory, thereby facilitating spontaneous behavior and having stimulant properties, while its effects at high BAC are sedative-hypnotic (Table 1). Acute alcohol poisoning (BAC > 40%) may result in death due to the formation of edema (swelling) in the base of the brain (medulla), where centers of respiratory and cardiovascular regulation are located. Behavioral reaction to alcohol intake depends upon several factors, including the rate of alcohol absorption, alcohol metabolism, and ► tolerance.
Alcohol is a molecule soluble in water, which has low lipid solubility and which, like water, is easily absorbed into the bloodstream from the stomach and the duodenum (the top part of the small intestine). Since the majority of absorption occurs in the duodenum, the absorption rate tends to be slower for the stronger spirits than for the beverages of medium alcohol content, such as wine, because the high alcohol content of spirits inhibits the opening of the pyloric valve that allows for the stomach contents to pass into the duodenum.
The mode of alcohol transport in and out of the cells is passive diffusion, which is determined by the concentration gradient across the cell membranes. Thus, the absorption of alcohol into the body tissues depends on the level of vascularization (blood supply) of those tissues as well as the alcohol concentration of the beverage. In healthy adults, 80-90% of absorption occurs in the first 30-60 min following ingestion, although this is delayed and reduced if food is present in the stomach. Table 2 presents the number of standard drinks required to obtain a given BAC. The gender difference in the achieved BAC and, consequently, in the behavioral effects of the same dose of alcohol is thought to be due to the difference in the distribution of the body mass between men and women (Graham et al. 1998). Men have higher ratio of muscles to fat than women and thus proportionally more blood in the body (fat tissue lacks blood supply). Consequently, the same amount of alcohol is more diluted in the blood of men than women and less will be absorbed into the tissues due to the lower concentration gradient. Additionally, women have been suggested to metabolize alcohol more slowly, due to reduced levels of the metabolizing enzyme, ► alcohol dehydrogenase (► ADH),
Alcohol. Table 1. Progression of behavioral changes corresponding to increased BAC (modified from Koob and Le Moal 2006).
Relief from anxiety
Social lubricant (more talkative, assertive, eloquent)
Significant disinhibition ("life of the party''
Impaired motor function
Marked ataxia (staggering;slurred speech)
Major motor impairment
Impaired reaction time
Increased sedation/hypnosis (stuporous but conscious)
Approaching general anesthesia
Lethal dose for 50% of nondependent drinkers
Biphasic alcohol effect
Biphasic alcohol effect
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