[Physiologic regeneration of rat salivary glands as dependent on age]

The power of the physiological regeneration of rat salivary glands has been investigated with 3H-thymidine by means of pulsee, double, and permanent marking as well as the technique of marked mitosis. Animals aged 12 hours up to 24 months were available. The transitory increase of regeneration seen in all the three salivary glands of the bead around the 5th day of life is explained as a consequence of the adaption to extrauterine life. From the second month of life on, the marking index is below 1 p.c. The growth fraction, which was determined by means of frequently repeated puls, and double, marking amounts to approximately 40 p.c. at the age of 19 hours, some 8 p.c. with 6-weeks-olds and as little as 1 or 2 p.c. at the age of 18 months. The determination of the cycle phases by double marking and the marked-mitosis technique revealed the relative constancy of the S, G2, and M-phases. With advancing age, the G1-phase extends. The salivary glands of the head can be classified as stable tissues according to the autoradiographic results.