We examined the effects of aging on the uptake of tritiated thymidine (3H-TdR) by the different cell types of the pancreas of the Syrian golden hamster. Animals, 8-22-wk-old, received3H-TdR (2 μCi/gm) intraperito-neally and were sacrificed 1 h later. Pancreatic tissue from each animal was processed for autoradiography. The percentage of acinar cells labeled with3H-TdR was 1.17 ±0.26 at 8-wk-old and steadily diminished to 0.02 ±0.00 at 22 wk. The percentage of ductular and islet cells labeled with3H-TdR at 8 wk was 0.24±0.24 and 0.16±0.01, respectively and at 22 wk was 0.13 ± 0.09 and 0.18 ±0.01, respectively. In contrast with acinar cells, the percentage of ductular and islet cells labeled with3H-TdR between 10- and 20-wk-old showed considerable variability. In the major ducts in the head of the gland, the number of epithelial cells per mm duct length labeled with3H-TdR did not change throughout the study; 3.25 ±1.5 at 8 wk and 3.35 ±1.3 at 22 wk. It is concluded that acinar cell growth is an inverse function of age between 8-22 wk and that differentiated cell types in the pancreas of the Syrian golden hamster are capable of incorporating3H-TdR during the S-phase of the ce
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