title: Circadian variations of epithelial cell proliferation in human rectal crypts.
abstract: OBJECTIVE
  Evidence (almost exclusively from animal studies) suggests that proliferation within the colorectal mucosa undergoes circadian variations. The epithelial cells that line the human colorectal crypt occupy definite positions along the longitudinal axis according to their proliferative potential and degree of differentiation. Thus, circadian rhythmicity was investigated in humans to locate the areas along the longitudinal crypt axis in which diurnal fluctuation might occur.
  
  
  METHODS
  Rectal mucosal biopsy specimens were obtained every 4 hours for a 24-hour span from each of 23 subjects (8 healthy volunteers and 15 with histories of sporadic adenomatous polyps). [3H]thymidine histoautoradiography was used to determine ratios of S-phase to total cells (total labeling index) in the crypt. Glands were also divided into 5 equal compartments from base (compartment 1) to mouth (compartment 5), and labeling indices were calculated for each.
  
  
  RESULTS
  Important temporal variations were confined to compartment 2 (F = 5.15, P = 0.0003) and total labeling indices (F = 3.57, P = 0.005). Despite individual variations, proliferation was generally higher at night and lower during afternoon. Upper-crypt proliferative rates (compartments 4 and 5) remained decidedly stable (F = 0.5, P = NS). Normal subjects and patients with polyps displayed similar circadian behaviors.
  
  
  CONCLUSIONS
  Circadian fluctuation in proliferation is confined to the area of the crypt normally associated with replication. Upper-crypt indices, including those that were higher than normal (a colon-cancer risk marker) are stable over 24 hours. These findings should be useful in planning chemoprevention trials and chemotherapeutic regimens.
authors.affiliation: Department of Internal Medicine, Catholic University of Rome, Largo F. Vito, Italy.
authors.forename: G
authors.initials: G
authors.lastname: Marra
authors.forename: M
authors.initials: M
authors.lastname: Anti
authors.forename: A
authors.initials: A
authors.lastname: Percesepe
authors.forename: F
authors.initials: F
authors.lastname: Armelao
authors.forename: R
authors.initials: R
authors.lastname: Ficarelli
authors.forename: C
authors.initials: C
authors.lastname: Coco
authors.forename: A
authors.initials: A
authors.lastname: Rinelli
authors.forename: F M
authors.initials: FM
authors.lastname: Vecchio
authors.forename: E
authors.initials: E
authors.lastname: D'Arcangelo
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D001345:Autoradiography; D002455:Cell Division; D002940:Circadian Rhythm; D005260:Female; D006801:Humans; D007413:Intestinal Mucosa / Q000166:cytology* / Q000378:metabolism; D008297:Male; D008875:Middle Aged; D012007:Rectum / Q000166:cytology* / Q000378:metabolism; D013936:Thymidine / Q000378:metabolism; D013997:Time Factors
chemical_list: D013936:Thymidine