Studies were conducted in mice to to determine the effects of circadian organization on 13 liver and six brain enzymes. Male CD2F1-mice were standardized either to 12 hours of light alternating with 12 hours of darkness or to the reversed dark/light cycle for 2 weeks. Mice in one group were 7 weeks old, while those in another group were 12 weeks old. Mice were killed at 3 hour intervals over a period of 2 days; brains and livers were removed and analyzed for enzymes. All 19 enzymes demonstrated a prominent circadian rhythm in at least one experiment. A statistically significant fit was noted by each rhythmic variable to a 24 hour cosine curve by the method of least squares. Liver enzymes showed their peak activities at the beginning of the dark cycle and initiation of the animal's activity. Brain enzymes peaked in activity at the beginning of the rest span and near the beginning of the light cycle. The beginning of the dietary intake process in the rodent normally occurs at the onset of darkness, and this may account for the clustering of the acrophases in enzyme activity at the beginning of the dark span. The phasing of each of the rhythms could be reversed within a 2 week period after reversing the environmental light/dark cycle by 180 degrees. The authors suggest this is the first study to simultaneously consider, from a chronobiological viewpoint, more than one or a few enzymes in the same animals in a single experiment.
Links with this icon indicate that you are leaving the CDC website.
The Centers for Disease Control and Prevention (CDC) cannot attest to the accuracy of a non-federal website.
Linking to a non-federal website does not constitute an endorsement by CDC or any of its employees of the sponsors or the information and products presented on the website.
You will be subject to the destination website's privacy policy when you follow the link.
CDC is not responsible for Section 508 compliance (accessibility) on other federal or private website.
For more information on CDC's web notification policies, see Website Disclaimers.
CDC.gov Privacy Settings
We take your privacy seriously. You can review and change the way we collect information below.
These cookies allow us to count visits and traffic sources so we can measure and improve the performance of our site. They help us to know which pages are the most and least popular and see how visitors move around the site. All information these cookies collect is aggregated and therefore anonymous. If you do not allow these cookies we will not know when you have visited our site, and will not be able to monitor its performance.
Cookies used to make website functionality more relevant to you. These cookies perform functions like remembering presentation options or choices and, in some cases, delivery of web content that based on self-identified area of interests.
Cookies used to track the effectiveness of CDC public health campaigns through clickthrough data.
Cookies used to enable you to share pages and content that you find interesting on CDC.gov through third party social networking and other websites. These cookies may also be used for advertising purposes by these third parties.
Thank you for taking the time to confirm your preferences. If you need to go back and make any changes, you can always do so by going to our Privacy Policy page.