Excretory @entity1568 metabolism in the juvenile @entity7547 XXXX : differences in aquatic and terrestrial environments.

@entity8777 @entity1568 @entity12116 @entity1522 @entity1133 @entity3265 @entity7547 @entity137 @entity7222
The fully grown but nonmetamorphosed (juvenile) @entity7547 @entity7547 was ureogenic and primarily ureotelic in water. A complete @entity7222 - @entity1133 cycle (OUC) was present in the liver. Aerial exposure impeded @entity1133 (but not @entity3265 ) excretion, leading to a decrease in the percentage of @entity1568 excreted as @entity1133 in the first 24 h. However, @entity1133 and not @entity3265 accumulated in the muscle, liver, and plasma during aerial exposure. By 48 h, the rate of @entity1133 excretion recovered fully, probably due to the greater @entity1133 concentration gradient in the kidney. It is generally accepted that an increase in @entity12116 synthetase activity is especially critical in the developmental transition from ammonotelism to ureotelism in the amphibian. Results from this study indicate that such a transition in A. mexicanum would have occurred before migration to land. Aerial exposure for 72 h exhibited no significant effect on @entity12116 synthetase-I activity or that of other OUC enzymes (with the exception of @entity7222 transcarbamoylase) from the liver of the juvenile A. mexicanum. This supports our hypothesis that the capacities of OUC enzymes present in the liver of the aquatic juvenile @entity7547 were adequate to prepare it for its invasion of the terrestrial environment. The high OUC capacity was further supported by the capability of the juvenile A. mexicanum to survive in 10 mM @entity8777 without accumulating @entity1522 in its body. The majority of the accumulating endogenous and exogenous @entity3265 was detoxified to @entity1133 , which led to a greater than twofold increase in @entity1133 levels in the muscle, liver, and plasma and a significant increase in @entity1133 excretion by hour 96. Hence, it can be concluded that the juvenile @entity7547 acquired ureotelism while submerged in water, and its hepatic capacity of @entity1133 synthesis was more than adequate to handle the @entity137 of endogenous @entity3265 during migration to land.
