Ureogenesis in chelonia

1. 1. Seven species of turtles, Gopherus berlandieri, Terrapene ornata, T. carolina, Clemmys insculpta, Pseudemys scripta, Chelydra serpentina and Trionyx muticus, were analyzed for ornithine-urea cycle enzyme activities and for the nitrogenous wastes in the blood, urine and bladder deposits. 2. 2. All species of turtles were ureogenic and ureotelic except for G. berlandieri, which was ureogenic but uricotelic. 3. 3. Freshly collected G. berlandieri showed undetectable levels of activity of argininosuccinate synthetase and low activity of argininosuccinate lyase, whereas dehydrated and fasted turtles showed higher activities. Also, in freshly collected Gopherus ammonia was most concentrated in blood while uric acid was highest in urine. In other Gopherus urea always predominated in blood and was high in urine. 4. 4. The rise in osmotic concentration that is associated with high urea levels in starved and dehydrated Gopherus may be important in reducing evaporative water loss during hibernation or times of stress. This would be especially important in the desert species.