The effect of short-term changes in the external salinity on the levels of the non-protein nitrogenous compounds and the ornithine-urea cycle enzymes in Rana cancrivora

Abstract

1. 1. Short-term changes in tissue osmolytes were examined in Rana cancrivora which had been exposed to media containing diluted sea water, saline, choline chloride, sucrose or mannitol. Estimations of the levels of the onithine-urea cycle enzymes were also made in some experiments. 2. 2. Progressive water depletion in muscle and live was observed on exposure to increasingly hyperosmotic environmental media, but the changes in tissue urea and non-essential amino acids were markedly greater than expected on the grounds of the change in water content alone. 3. 3. Lysine was notable in being decreased in hyperosmotic media compared to fresh water. 4. 4. An alteration in the activity of argininosuccinate synthetase was observed after 2 days' exposure to hyperosmotic media, but no significant concomitant change in carbamoyl phosphate synthetase could be detected. 5. 5. It is concluded that the initial elevation of the tissue urea concentration does not result simply from a generalized increase in biosynthesis of the enzymes of the ornithine-urea cycle.