The mechanism(s) of ammonia excretion in the presence of elevated external ammonia are not well understood in fish. Recent studies in other organisms have revealed a new class of ammonia transporters, Rhesus glycoprotein genes (Rh genes), which may also play a role in ammonia excretion in fish. The first objective of this study was to clone and characterize Rh genes in a fish species with a rel...

The climbing perch, Anabas testudineus, inhabits large rivers, canals, stagnant water bodies, swamps and estuaries, where it can be confronted with aerial exposure during the dry season. This study aimed to examine nitrogen excretion and metabolism in this fish during 4 days of emersion. Contrary to previous reports, A. testudineus does not possess a functional hepatic ornithineurea cycle becau...

Ammonia excretion from the gill in teleost fish is essential for nitrogen elimination. Although numerous physiological studies have measured ammonia excretion, the mechanism of ammonia movement through the membranes of gill epithelial cells is still unknown. Mammalian Rh glycoproteins are members of a family of proteins that mediate ammonia transport in bacteria, yeast, and plants. We identifie...

In 1921 Nash and Benedict (11) advanced the hypothesis that urinary ammonia is formed in the kidney from some precursor in the blood. This conclusion was based upon the observation that the concentration of ammonia was higher in the renal vein than in the renal artery, that the quantity of ammonia in arterial blood was too small to supply the ammonia found in the urine, and that the arterial am...

To evaluate the effects of chronic metabolic acidosis on protein dynamics and amino acid oxidation in the human kidney, a combination of organ isotopic ((14)C-leucine) and mass-balance techniques in 11 subjects with normal renal function undergoing venous catheterizations was used. Five of 11 studies were performed in the presence of metabolic acidosis. In subjects with normal acid-base balance...

We investigated relationships among branchial unidirectional Na(+) fluxes, ammonia excretion, urea excretion, plasma ammonia, plasma cortisol, and gill transporter expression and function in three freshwater fish differing in their sensitivity to high environmental ammonia (HEA). The highly ammonia-sensitive salmonid Oncorhynchus mykiss (rainbow trout), the less ammonia-sensitive cyprinid Cypri...

We tested the role of increased ammonia in urine as an energy- and/or nitrogen (N)-saving mechanism in the great fruit-eating bat Artibeus lituratus (Phyllostomidae). We compared N excretion in two groups of bats fed energy-rich (2.75 kJ g(-1) wet mass) or energy-poor diets (0.7 kJ g(-1) wet mass). Within each diet, bats were assigned to different N contents. In order to function as an energy-s...

Emissions of ammonia, as well as other gases and particulates, to the atmosphere are a growing concern of livestock producers, the general public, and regulators. The concentration and ruminal degradability of CP in beef cattle diets may affect urinary and fecal excretion of N and thus may affect ammonia emissions from beef cattle feed yards. To determine the effects of dietary CP concentration...

Ammonia and urea are the primary forms of nitrogen excretion in teleost fish. There exists, however, a discrepancy between the sum of ammonia plus urea nitrogen and total nitrogen, indicating that 'unknown' nitrogen end products may play an important role in nitrogen metabolism. The current study analysed a wide range of nitrogen end products in both fed and fasted juvenile rainbow trout. Ammon...

Krogh (1939) first suggested that in freshwater animals branchial or cutaneous excretion of ammonia may be related to sodium absorption. In both freshwater Crustacea (Astacus pallipes) and teleosts (Carassius auratus) independent active transport of Na and Cl~ from the outside medium have been definitely established (Shaw, 1960 a—c; Garcia Romeu & Maetz, 1964). Sodium in particular may be absor...