Circaseptan (about 7-day) modulation of circadian rhythm in corneal mitoses of Holtzman rats.

An infradian modulation with a 168 h or circaseptan period characterizes epithelial corneal mitoses in adult female and male Holtzman rats, standardized at 24 +/- 1 degree C and approximately 50% relative humidity on six different sequences of light (L) alternating every 12 h with darkness (D). To approximate sampling over a 24 h LD span by convenient sampling within a single hour, the LD 12:12 regimen was staggered by 4 h in the six environments. Bedding was changed 3 days before each day of killing. During each of eight or 12 consecutive days, male and female rats, respectively, were killed and the eyeballs were removed. Mitotic indices in the cornea were determined separately for each eye and the data were analyzed by linear and nonlinear least-squares rhythmometry. For a prominent circadian component of mitotic activity, the 95% confidence interval (CI) of the period extends from 23.6 to 24.3 h for the data from males and from 23.7 to 24.2 h for those from female rats. The circadian amplitude is larger in males as compared to females. The peaks in the 24 h cosine functions best approximating the data, the circadian acrophases, are at -64 degrees or -48 degrees, i.e., 4 h 16 min or 3 h 12 min from lights-on in male and female rats, respectively. In the data from the two genders, the 24 h synchronized circadian acrophases are thus only 16 degrees, i.e., 1 h and 4 min apart. A test for an anticipated circaseptan (7-day) period shows that this particular infradian periodicity is superimposed upon the circadian one in data from both genders.(ABSTRACT TRUNCATED AT 250 WORDS)