Chemical, biological, and physical processes lead to distinctive “isotopic signatures” in biological materials that allow tracing of the origins of organic substances. Isotopic variation has been extensively used by plant physiological ecologists and by paleontologists, and recently ecologists have adopted the use of stable isotopes to measure ecosystem patterns and processes. To date, animal physiological ecologists have made minimal use of naturally occurring stable isotopes as tracers. Here we provide a review of the current and potential uses of naturally occurring stable isotopes in animal physiological ecology. We outline the physical and biological processes that lead to variation in isotopic abundance in plants and animals. We summarize current uses in animal physiological ecology (diet reconstruction and animal movement patterns), and suggest areas of research where the use of stable isotopes can be fruitful (protein balance and turnover and the allocation of dietary nutrients). We argue that animal physiological ecologists can benefit from including the measurement of naturally occurring stable isotopes in their battery of techniques. We also argue that animal physiologists can make an important contribution to the emerging field of stable isotopes in biology by testing experimentally the plethora of assumptions upon which the techniques rely.

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Natural Abundance Variations in Stable Isotopes and their Potential Uses in Animal Physiological Ecology

Excerpt INTRODUCTION Sophisticated biochemical studies in recent years have revealed that the regulation of intracellular metabolism is a logical, orderly, and intricate process Control of enzyme 

Hypoxanthine-Guanine Phosphoribosyltransferase Deficiency in Gout

Use of exogenous and endogenous urea for protein synthesis in normal and uremic subjects.

Human milk intake and growth in exclusively breast-fed infants.

A theoretical basis for increasing current estimates of the amino acid requirements in adult man, with experimental support.

"Unessential" nitrogen: a limiting factor for human growth.

The excretion of oxypurine metabolites in urine of patients with congenital hyperuricosuria exceeds, on a creatinine basis, that observed in any previously recognized metabolic anomaly. The ratio of hypoxanthine to xanthine is from 2:1 to 3:1 and results from increased hypoxanthine excretion, in contrast to other hyperuricosuric conditions where ratios of less than one have been reported. Administration of allopurinol (a xanthine-oxidase inhibitor) reduces the excretion of uric acid but results in an equivalent increase in xanthine and hypoxanthine. These features appear to be unique to congenital hyper-uricosuria.

M. Earl Balis

Papers

"Unessential" nitrogen: a limiting factor for human growth.

Urinary metabolites in congenital hyperuricosuria.

A method for the prenatal diagnosis of congenital hyperuricemia

Immunochemical studies of AMP:pyrophosphate phosphoribosyltransferase from normal and Lesch—Nyhan subjects

Hemoglobin metabolism in the premature infant.