Regulation of Hepatic Glycogen Synthetase of Rana catesbeiana

Interrenal activity during metamorphosis of the tiger salamander, Ambystoma tigrinum

Plasma corticosterone concentrations were low in premetamorphic tiger salamander larvae (Norman Stage I; M. F. Norman (1985) Anat. Rec. 211, 102-109). Corticosterone levels were significantly elevated at midmetamorphosis (Norman Stage IV) but decreased at the end of metamorphosis (Norman Stage VII). Corticosterone levels remained low 2 weeks after metamorphosis. Interrenal 3 beta-hydroxysteroid dehydrogenase activity was low in premetamorphic larvae (Norman Stage I) but was significantly elevated by midmetamorphosis (Norman Stage IV) and remained elevated at the end of metamorphosis (Norman Stage VII). There were no significant changes in interrenal cell nuclear size during metamorphosis. There was a significant decrease in body weight as well as a significant increase in hematocrit accompanying metamorphosis. The increase in plasma corticosterone concentration seen during metamorphosis of the tiger salamander is accompanied by an increase in interrenal steroidogenesis.

Morphometry of pancreatic beta cell populations during larval growth and metamorphosis of Rana catesbeiana

Insulin secreting (beta) cell and pancreas volumes were estimated from bullfrogs at different stages in the life cycle. Estimations were made after immunostaining and planimetry of serial pancreas sections. The beta cell volume increased during larval life and is the most likely source of the increased insulin-like immunoreactivity extracted from tadpole pancreases (J. Hulsebus and E. S. Farrar (1985) Gen. Comp. Endocrinol. 58, 114-119). Metamorphic climax was associated with a loss of pancreas and beta cell volumes and insulin-like immunoreactivity. The beta cell pancreatic volume increased following metamorphosis and growth continued in juveniles and adults. The beta cell mass formed a relatively constant percentage of the total pancreatic volume throughout the life cycle.

Thyroxine elicits divergent changes in mRNA levels for two urea cycle enzymes and one gluconeogenic enzyme in tadpole liver

Thyroxine-induced metamorphosis of the tadpole to the frog (Rana catesbeiana) is marked by increased activities of the urea cycle enzymes in liver. Cloned cDNAs for two mammalian urea cycle enzymes--carbamyl-phosphate synthetase I and argininosuccinate synthetase--were shown to cross-hybridize with the corresponding mRNAs in tadpole liver. Thyroxine treatment produced nearly 10-fold, coordinate increases in hybridizable mRNA levels for these two enzymes in tadpole liver. This increase is sufficient to account for reported increases in enzyme levels and synthesis rates, demonstrating that thyroxine largely regulates concentrations of these enzymes at a pretranslational step(s). In contrast, levels of phosphoenolpyruvate carboxykinase mRNA in tadpole liver decreased by more than 90% following thyroxine treatment. This differs from the thyroxine-induced increases in synthesis rates of enzyme and mRNA reported for phosphoenolpyruvate carboxykinase in rat liver. However, the decreased levels of this mRNA in tadpole liver may represent a secondary response due to thyroxine-stimulated release of insulin.