Adaptive hyperplasia and compensatory growth in the salt glands of ducks and geese.

1. The incorporation of [3H]thymidine into salt-gland DNA has been studied in vivo and in vitro during adaptation of birds to salt water. 2. No increase in [3H]thymidine incorporation in vivo was apparent in birds on salt water for 0.25 and 1 day compared with those on fresh water. However, by 2 days there was a marked increase. At 7 and 14 days, incorporation was again low but by these later stages the DNA content of the glands was significantly increased. 3. Increased incorporation of [3H]thymidine was also evident in salt-gland slices incubated in vitro from birds on salt water for 2 or 4 days, but not for 14 days, compared with those on fresh water. 4. It is concluded that hyperplasia, as well as the hypertrophy demonstrated previously, occurs as part of the over-all adaptive response of the salt glands during the continual ingestion of salt water, but that the time course of the two processes is different. 5. In geese with one salt gland removed, no indication of compensatory growth of the remaining gland was evident in birds kept on fresh water for 24 days. In such birds on salt water for 14 days, some compensatory growth occurred but, as judged by measurements of DNA, RNA and protein, this could be ascribed to hypertrophy.