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Biomedical subjects

R P Forster

Publications and source records attributed to R P Forster.

At least 19 recordsLinked to original sources
PubMed1982

Renal handling of taurine in marine fish.

Net renal tubular excretion of taurine was demonstrated by clearance techniques in the dogfish, Squalus acanthias; the little skate, Raja erinacea; and in the winter flounder, Pseudopleuronectes americanus. Dogfish acclimated to 70% seawater had increased renal excretion of taurine resulting from higher glomerular filtration rates of taurine as well as from increased rats of tubular secretion. Tubular secretion of taurine prevailed in the dogfish and flounders measured, whereas it occurred in only 30% of the population of skates where tubular reabsorption predominated. Taurine uptake into incubated dogfish thin kidney slices was investigated. Uptake occurs mainly across the peritubular membrane, is carrier mediated, dependent on metabolic energy, and completely inhibited by ouabain and low Na in the medium. The active transport of taurine is also inhibited by beta-alanine but not by alpha-aminoisobutyric acid, glycine, gamma-aminobutyric acid, PAH, or probenecid.

Animals↗
PubMed1977

Free amino acids in tissues of the skate Raja erinacea and the stingray Dasyatis sabina: effects of environmental dilution.

Concentrations of individual free amino acids were determined in various tissues of the skate (Raja erinacea) and the stingray (Dasyatis sabina), and the relationship of cellular free amino acid concentrations to intracellular osmoregulation was investigated by adapting these elasmobranchs to half-strength seawater. Each tissue characteristically had high levels of certain specific amino acids. Skate sing muscle contained high concentrations of sarcosine and beta-alanine, skate heart had high concentrations of taurine, and skate erythrocytes had high levels of taurine and beta-alanine. Amino acid levels in skate plasma were very low. High concentrations of aturine and glutamate were found in stingray brain. Adaptation of skates and stingrays to half-strength seawater was accompanied by significant decreases in concentrations of the major free amino acids in skate wing muscle and erythrocytes and in stingray brain, but not in skate heart. The data suggest that in these elasmobranchs certain specific free amino acids are selectively involved in intracellular osmoregulatory mechanisms.

Adaptation, Physiological↗
PubMed1976

Intracellular osmoregulatory role of amino acids and urea in marine elasmobranchs.

Little skates, Raja erinacea, and stingrays, Dasyatis americana, were gradually transferred over a period of 4-5 days from full strength to approximatley 50% seawater. Plasma and muscle osmolarity fell. Hematocrits were essentially unchanged. Extracellular fluid volume (ECF) of muscle, estimated as the chloride space, increased 70% during this period. Regulation of muscle cell volume was associated with sharp declines in cellular concentrations of total amino acids (ninhydrin-positive materials) and urea. The osmoregulatory importance of the free amino acid pool in erythrocytes and muscle was a particularly prominent feature in both species. Intracellular amino acid concentration in R. erinacea muscle fell from 214 to 144 mmol/liter during transfer to 50% seawater, urea from 398 to 264, and trimethylamine oxide (TMAO) dropped from 63.9 to 35.8 mmol/liter. TMAO plasma levels were similar in stingray and skate, but muscle TMAO concentrations were much higher in the former. Urea content in stingray plasma greatly exceeded that in R. erinacea-630 and 574 mmol/liter in two specimens-perhaps the highest recorded.

Amino Acids↗
PubMed1967

Lungfish Neoceratodus forsteri: activities of ornithine-urea cycle and enzymes.

The level of activity of the ornithine-urea cycle is low in the liver of the permanently aquatic Australian lungfish. The rate of incorporation of (14)C-bicarbonate into urea by liver slices was only 100th of that previously observed in the estivating African lungfish Protopterus dolloi. The activities of enzymes of the ornithine-urea cycle were similarly reduced. The low activity of this cycle in Neoceratodus is consistent with its exclusively aquatic nature.

Animals↗
PubMed1966

Urea synthesis in the lungfish: relative importance of purine and ornithine cycle pathways.

The relative importance of the purine pathway (uricolysis) and the ornithine cycle as routes for urea synthesis was assessed in isolated liver preparations from the African lungfish Protopterus dolloi. Incorporation of C(14)-labeled precursors into urea was used for comparison. Both pathways are present in the lungfish, but the ornithine cycle is quantitatively more important.

Animals↗