This finding, that some level of alcohol consumption might increase testosterone in the brain for some individuals, could explain why alcohol causes some people to become aggressive while intoxicated. It could also explain some other behavioral effects associated with increased testosterone levels, such as increased libido, the authors suggested. “We have demonstrated that there are very different results in the way two different groups of male rats form testosterone after acute administration of alcohol,” said Robert H. Purdy, of The Scripps Research Institute and senior author of the study. “These differences in animals may reflect similar individual differences in humans, and provide new insights for understanding individual differences in the behavioral and endocrine pathology associated with alcohol abuse.“
Neuroactive Steroids Measured
According to the published report, researchers “injected either alcohol or 1,1-dideuteroethanol (2 g alcohol/kg body weight) into the abdominal cavities of two groups of rats, 30 un-operated and 24 adrenalectomized and castrated (ADX/GDX) Wistar males. 1,1-dideuteroethanol is a nonradioactive form of alcohol in which two of the hydrogen atoms on carbon atom #1 of ethanol have been replaced by deuterium atoms, which can then be traced.“ They then used mass spectrometry to determine both the number of neuroactive steroids present and the degree of deuterium in specific neuroactive steroids isolated from brain samples.
Fourfold Increase in Testosterone
The investigators found that concentrations of testosterone increased fourfold in the frontal cortex and threefold in the plasma of the unoperated rats 30 minutes after alcohol administration. ADX/GDX rats had testosterone concentrations that were only 5% of those found in the unoperated rats after alcohol injection. The findings demonstrated that alcohol oxidation is directly linked to testosterone biosynthesis, the authors said.
Direct Alcohol-Testosterone Link Unanticipated
“Our finding of a direct link between alcohol administration and the level of the neuroactive steroid testosterone in the brain of these experimental animals was unanticipated from prior studies with another species of rats,” Purdy said. “Although many other studies clearly demonstrate that chronic consumption of high dosages of alcohol appears to be consistently inhibitory and suppresses reproductive function,” said Dennis D. Rasmussen, research associate professor in the department of psychiatry at the University of Washington, “this study raises the possibility that episodes of alcohol consumption may also at least temporarily increase testosterone levels, with the direction of the response likely being dependent upon a variety of factors, including dosage and personal characteristics.” “This particular dosage produced blood alcohol levels and behavioral responses consistent with intoxication. So, alcohol consumption, under at least some conditions and by at least some individuals, may acutely stimulate testosterone levels in the plasma and brain of both males and females and thus could elicit some of the behavioral effects associated with increased testosterone levels, such as increased libido or aggression.”
The Role of Testosterone and Alcohol’s Effects
The study’s findings join those of other studies in which alcohol administration increased plasma testosterone levels in a gender- and dose-dependent manner. “Together these studies are important,” he said, “because they illustrate that what has become a largely accepted principle—that alcohol consumption inhibits plasma testosterone levels and reproductive function—is not universally true.” Rasmussen suggested that future research builds upon and adds to previous findings regarding alcohol’s effects on testosterone.
Does Tolerance Develop Over Time?
“It would be important to determine whether lower dosages of alcohol, which do not induce rapid pronounced intoxication and ataxia, would also produce the acute increase in testosterone, and whether this response to lower dosages would be consistent across different strains of rats. Also, does tolerance develop with repeated administrations?” he asked. “Does this increase in testosterone occur following elective self-administration of alcohol?” Rasmussen said. “Finally, and probably most interesting, what role might the demonstrated changes in testosterone play in behavioral responses to acute ethanol consumption? Are there gender differences in these responses? And, if the responses do occur in females, are they different during different stages of a woman’s cycle?”
