The Effects of the Presence or Absence of the Pituitary Gland on the Daily Rhythmicity of Mitotic Rates in Urodele Larval Tissues

Abstract

When bihourly determinations are made of the mitotic rates of a number of urodele larval tissues, a rhythmic pattern over the 24-hour period manifests itself. Periodicity has been described for the mitotic rates of larval epidermis (Scheving, Chiakulas and Abzug, 1959), gastric mucosal epithelium (Chiakulas and Scheving, 1961), corneal epithelium (Scheving and Chiakulas, 1962) and the hemopoietic tissue of the cortical zone of the liver (Chiakulas and Scheving, 1964). In all the tissues investigated, a bimodal pattern of rhythmicity has been found, with one peak in the rate of cell division occurring during the hours of light and another peak during the hours of darkness. The original study on epidermis and the subsequent ones on gastric mucosal epithelium and the hemopoietic tissue of the liver, compared the mitotic rates in these tissues of larvae collected at 2-hour intervals from the natural pond environment to the rates found in the tissues of laboratory-reared animals. In both pond-reared and laboratory-reared larvae, a basic bimodal rhythmic pattern of the mitotic rates is found with only minor differences in the timing of the peak and trough values, although a considerable difference in the magnitude of mitotic rates of the tissues occurs between the two groups.

This investigation was supported by Research Grant No. 17140 from The National Science Foundation. Participation in the VIIIth International Congress of Anatomists was enabled by Research Grant No. 8147 from The United States Public Health Service, National Institutes of Health.