Updated July 12, 2013.
Females are not only less sensitive to the sedating effects of alcohol, researchers at Duke University Medical Center have found that the cycling hormonal levels of women can mediate alcohol's effects, making them more vulnerable to negative consequences of drinking.
"Despite the fact that men outnumber women in terms of having alcohol-related problems, women are more vulnerable to many of the effects of alcohol use," said the study's first author, Young May Cha, a research analyst at Duke University Medical Center.
"In both humans and animal models, females can drink less and for a shorter period of time, and yet experience the same level of effects produced in males. This 'telescoping' phenomenon strongly suggests that there is something unique about the female sex that lends it to being so susceptible to alcohol's effects."
Cha and her colleagues used laboratory rats to examine what effects the adult females' estrous cycles might have on alcohol's effects.
"The four stages of the rat estrous cycle can be viewed as similar to the different stages of the human menstrual cycle," she explained. "In both humans and rats, sex hormone levels rise and fall in a cyclical pattern. Furthermore, rats are a useful and practical model to study these hormone fluctuations because the estrous cycle is relatively short; it is only four to five days long."
Researchers gave adolescent and adult male and female rats five grams of alcohol then observed their lost of righting reflex, and measured their inhibitory process by measuring GABAA receptor-mediated IPSCs.
The researchers were able to describe the behavioral difference between the effects of alcohol on males and females, and also to observe a possible mechanism at the cellular level.
"The female rodents' lesser sensitivity, compared with the adult males, to the behavioral sedative effects of alcohol was most pronounced in the proestrous (the first phase of the estrous cycle, which corresponds to the onset of mating behavior) and diestrous (the last phase of the estrous cycle) states," the researchers reported.
"Our study shows that when you control for that, and just look at the potency of alcohol on the brain mechanisms that cause sedation, females actually appear to be less sensitive to alcohol. Furthermore, the study emphasizes the need to explore how factors associated with the estrous cycle (or menstrual cycle in humans) may mediate this effect."
"Although we live in a society that favors equality between the sexes, men and women are not equal when it involves being affected by alcohol," Cha said. "In particular, this study's findings suggest that women, as the gender less affected by alcohol's sedative effects, should take greater care when gauging how much they have had to drink."
Source: Cha's study was published in the January 2006 issue of Alcoholism: Clinical & Experimental Research.
Females are not only less sensitive to the sedating effects of alcohol, researchers at Duke University Medical Center have found that the cycling hormonal levels of women can mediate alcohol's effects, making them more vulnerable to negative consequences of drinking.
"Despite the fact that men outnumber women in terms of having alcohol-related problems, women are more vulnerable to many of the effects of alcohol use," said the study's first author, Young May Cha, a research analyst at Duke University Medical Center.
"In both humans and animal models, females can drink less and for a shorter period of time, and yet experience the same level of effects produced in males. This 'telescoping' phenomenon strongly suggests that there is something unique about the female sex that lends it to being so susceptible to alcohol's effects."
Cha and her colleagues used laboratory rats to examine what effects the adult females' estrous cycles might have on alcohol's effects.
"The four stages of the rat estrous cycle can be viewed as similar to the different stages of the human menstrual cycle," she explained. "In both humans and rats, sex hormone levels rise and fall in a cyclical pattern. Furthermore, rats are a useful and practical model to study these hormone fluctuations because the estrous cycle is relatively short; it is only four to five days long."
Researchers gave adolescent and adult male and female rats five grams of alcohol then observed their lost of righting reflex, and measured their inhibitory process by measuring GABAA receptor-mediated IPSCs.
The researchers were able to describe the behavioral difference between the effects of alcohol on males and females, and also to observe a possible mechanism at the cellular level.
Hormonal Fluctuations
"The promotion of GABA-mediated neuronal inhibition is thought to be a primary mechanism of alcohol-induced sedation, and may also account for some of its anti-anxiety effects," explained Scott Swartzwelder, professor of psychiatry at Duke and senior author of the study. "This measurement is particularly significant in our study because it correlates with the result that the females are less sensitive to alcohol-induced sedation. Since these measurements are made in isolated brain sections, the effects cannot be due to sex differences in alcohol absorption or elimination in the body.""The female rodents' lesser sensitivity, compared with the adult males, to the behavioral sedative effects of alcohol was most pronounced in the proestrous (the first phase of the estrous cycle, which corresponds to the onset of mating behavior) and diestrous (the last phase of the estrous cycle) states," the researchers reported.
Less Sensitive to Alcohol
"We know that females are affected by alcohol differently than males," said Swartzwelder, "but unlike many studies, this one shows a way in which females are less sensitive than males. People generally think that alcohol is more potent in females, but that is because women are smaller than men and it generally takes fewer drinks for them to become impaired."Our study shows that when you control for that, and just look at the potency of alcohol on the brain mechanisms that cause sedation, females actually appear to be less sensitive to alcohol. Furthermore, the study emphasizes the need to explore how factors associated with the estrous cycle (or menstrual cycle in humans) may mediate this effect."
Women Should Take Greater Care
Cha said the study also shows that "adolescent male and female rats are similarly sedated by alcohol, but that adult male and female rats are not. This result suggests that as humans mature from adolescence to adulthood, women may become less sensitive to alcohol-induced sedation than men do. This change may have consequences for the ability of an adult woman to physiologically gauge how impaired she is becoming as she drinks.""Although we live in a society that favors equality between the sexes, men and women are not equal when it involves being affected by alcohol," Cha said. "In particular, this study's findings suggest that women, as the gender less affected by alcohol's sedative effects, should take greater care when gauging how much they have had to drink."
Source: Cha's study was published in the January 2006 issue of Alcoholism: Clinical & Experimental Research.
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