Comparison of the Circadian Rhythm in Cell Proliferation in Corneal Epithelium of Male Rats Studied Under Normal and Hypobaric (Hypoxic) Conditions

Abstract

Groups of 20-45-day-old rats maintained on a light (0600–1800)/dark (1800–0600) regimen with food and water available ad libitum were studied for the effect of hypoxic hypoxia on the circadian rhythm of corneal epithelial mitosis and thymidine incorporation. In experiments conducted during the months of September and November, hypoxic hypoxia was accomplished by the exposure of rats to a simulated altitude of 7500 m in one series of experiments, or to a gaseous mixture of 8% oxygen and 92% nitrogen at sea level atmospheric pressure (760 mmHg) in another series of experiments. Controls were included as well. Statistically significant (P < 0.05) circadian rhythmicity in the corneal mitotic index was substantiated in the control animals with mesor (AT) =12.4%, amplitude (A) = 9.6% and acrophase (ø) of 0911. In the hypoxic hypoxia situation, the mesor and amplitude were depressed to 8.6 and 5.9%, respectively. In control groups, thymidine incorporation was circadian rhythmic with M= 38.5 and A = 11.3cpm/μ;m DNA and acrophase of 2255. In the hypoxic hypoxia situation, the mesor was similar to the controls; whereas the amplitude was suppressed to 6.1% and acrophase was phase advanced by about 7 hr. Changes in the circadian rhythm of corneal mitosis and in thymidine incorporation under hypoxic hypoxia can be explained by programmed-in-time energy requirements during the corneal cell regeneration cycle.

Key Words:

• Key words–Circadian rhythm
• corneal mitotis
• DNA thymidine incorporation
• hypoxic hypoxia
• rats