The comparative role of haemoglobinaemia and hypoxia in the development of canine babesial nephropathy.

Renal pathology associated with haemoglobinaemia resulting from Babesia canis infection is ascribed to haemoglobinuria, with or without a contribution from anaemic hypoxia. This study was undertaken to investigate the relative roles of haemoglobinaemia and hypoxia in renal function and pathology in the dog. Three groups of 6 dogs each were used over a 4-day period. The dogs in the 1st group were infused with homologous canine haemoglobin, anaemic hypoxia was induced in the 2nd group, and both treatments were applied in the 3rd group. Full urinalyses, serum urea and creatinine concentrations, fractional clearance of sodium and the activity of urine enzymes, were assessed daily. At the end of the trial period, the glomerular filtration rate (GFR) was determined and kidney specimens collected for light and electron microscopy. In the group with hypoxia only, the urine sediment contained more casts and a greater number of renal tubular epithelial (RTE) cells than in either of the other groups. Hypoxia resulted in greater enzymuria, suggestive of RTE cell pathology, whereas haemoglobinuria did not appear to have any effect on urine enzyme activity. Hypoxia resulted in a decreased GFR. Histological examination revealed a mild, single-cell tubular necrosis in the majority of the animals (all 3 groups), with granular casts in the hypoxic groups. There appeared to be a large individual variation in the ability of the kidney to handle infused haemoglobin. It was concluded that severe haemoglobinaemia did not induce a significant nephropathy, anaemic hypoxia appeared to cause a very mild nephropathy, and the combination of haemoglobinaemia and anaemic hypoxia did not exacerbate this change. These lesions were very different from those described in canine babesiosis.