Partitioning of Nitrogen Excretion between Urea and Ammonia and between Skin and Kidneys in the Aquatic CaecilianTyphlonectes natans

Nitrogen excretion was studied in the aquatic caecilian Typhlonectes natans by analyzing samples of the bathing medium over an 8-h period for total ammonia (Tamm: NH₃ + \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage{wasysym} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document}$${\mathrm{NH_{4}^{+}}}$$\end{document}) and urea. Total ammonia was excreted at a rate of 0.35 μM · 10g⁻¹ · h⁻¹, while urea was excreted at a rate of 0.19 μM · 10g⁻¹ · h⁻¹. When excretion is expressed in molar equivalents of nitrogen, ammonia-N excretion was 0.35 μatm N · 10g⁻¹ · h⁻¹ while urea-N excretion was 0.38 μatm N · 10 g⁻¹ · h⁻¹. These latter values uwere not significantly different. Plasma Tamm concentration was 1.3 mM, while plasma urea concentration was 4.4 mM. Urine Tamm concentration was 3.8 mM, while urine urea concentration was 2.7 mM. Partitioning Tamm excretion between skin and kidneys found 1.11 μM · 10 g⁻¹ · h⁻¹ ammonia excreted across the skin. The kidneys contributed 0.09 μM · 10 g⁻¹ h⁻¹, or less than 8%. Skin urea excretion rate was 0.21 μM · 10 g⁻¹ · h⁻¹, while the kidneys accounted for 0.08 μM · 10 g⁻¹ · h⁻¹, or less than 28%.