Mycotoxins and the avian kidney: assessment of physiological function

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Abstract
The avian kidney has shown a remarkable ability to maintain adequate and even normal function in the face of a mycotoxin challenge. Full evaluation of the nephrotoxicity of a substance must therefore go beyond pathological and ultrastructural documentation and include a complete functional evaluation. To date, only three nephrogenic mycotoxins, citrinin, ochratoxin A, and aflatoxin B1 have been assessed for their ability to alter avian renal function. At non-lethal doses, citrinin appears to have acute reversible effects on the distal portion of the nephron, possibly acting to inhibit water absorption. Ochratoxin A is more potent and less acute than citrinin but less site-specific in that both proximal and distal tubules are damaged, resulting in severe loss of both fluids and electrolytes. Aflatoxin B1 at a dosage and duration which induced hepatotoxicity, concurrently exerted nephrogenic effects such as increased urinary calcium excretion and decreased inorganic phosphate excretion. In commercial broilers aflatoxin B1 has been shown to decrease plasma levels of 25-hydroxy vitamin D, 1,25-dihydroxy vitamin D and may also decrease endogenous parathyroid hormone synthesis and the renal sensitivity to parathyroid hormone. Furthermore, exposure to aflatoxin B1 may cause prolonged alteration in renal function such as reduced glomerular filtration rate. This review summarizes the studies which have been conducted to evaluate avian renal function during both acute and chronic exposure to these three mycotoxins.

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