Comparative physiology of glomerular filtration rate by plasma clearance of exogenous creatinine and exo-iohexol in six different avian species

Abstract

Early diagnosis of kidney diseases in avian species is limited. Endogenous markers currently used in avian practice are not sensitive enough to identify early kidney failure. Consequently, alternative markers should be evaluated. To be able to evaluate these alternative markers, an accurate marker to estimate the GFR should be validated. This study determined the GFR, measured as clearance of exogenous creatinine and exo-iohexol, in six different bird species, i.e. broiler chickens, laying chickens, turkeys, Muscovy ducks, pigeons and African grey parrots (4♀/4♂). To be able to compare the six bird species, normalization to bodyweight (BW) of the GFR was performed, after a good correlation between BW and kidney weight was demonstrated (R² = 0.9836). Clearance of exo-iohexol normalized to BW (mL/min/kg) was determined in all bird species, i.e. 3.09 in broiler chickens; 2.57 in laying chickens; 1.94 in turkeys; 1.29 in pigeons; 2.60 in ducks and 1.11 in parrots. However, these results differed significantly with the clearance of exogenous creatinine: 8.41 in broiler chickens; 9.33 in laying chickens; 5.62 in turkeys; 14.97 in pigeons; 17.59 in ducks and 25.56 in parrots 25.56. Iohexol is preferred to measure the GFR, since it is not prone to tubular reabsorption nor secretion.

Simultaneous Measurement of Glomerular Filtration Rate, Effective Renal Plasma Flow and Tubular Secretion in Different Poultry Species by Single Intravenous Bolus of Iohexol and Para-Aminohippuric Acid

“…The GFR estimated based on exogenous creatinine clearance in pigeons in the study of Scope et al was similar (6.30 mL/min/kg) to the observed results in the presented study based on IOH clearance [17]. However, IOH was preferred to creatinine to measure the GFR in avian species, since it is not prone to tubular reabsorption nor secretion [5]. Furthermore, the sampling volume in pigeons was smaller in this study compared to the other poultry species, since collecting larger volumes of blood in smaller avian species is ethically not possible.…”

“…The results of the clearance of exo-IOH in the study of Gasthuys et al were highly comparable to the results in this study for broilers, turkeys, and ducks (GFR exo-IOH (mL/min/kg) was: broiler chickens: 3.09; layer chicken: 2.57; turkey: 1.94; pigeon: 1.29; duck: 2.60; parrot: 1.11). However, a higher clearance of IOH was observed in this study for layers and pigeons [5].…”

“…This approach is a basic mathematical tool for analyzing differences in anatomy, physiology, biochemistry, and pharmaco-/toxicokinetics in animals of different sizes. Recently, a good correlation between the GFR and BW in different avian species has been demonstrated [5]. However, it is not known if the eRPF or TS obtained in one avian species might be extrapolated to other avian species.…”

“…IOH, a water soluble non-toxic monomer, is neither reabsorbed nor secreted by the renal tubules, with low hypertonicity as an additional advantage [3]. Recently, the clearance of an intravenous (IV) IOH bolus administration was applied as a sensitive marker to assess the GFR in six different bird species [5].…”

Iohexol-based measurement of intestinal permeability in birds

“…[15] In avian species, iohexol has already been used as a safe and well-tolerated contrast medium, especially for radiographic studies of the gastrointestinal tract as well as to measure the glomerular filtration rate of the kidneys. [16][17][18] In birds, intestinal disorders as complex as IBD are rarely described, but evidence suggests that inflammatory conditions of the intestines in the form of chronic wasting disease exist in a similar pattern in avian species as they do in mammals. [19,20] Furthermore, feed restriction or experimentally-induced enteropathies in poultry can disrupt the intestinal barrier function, resulting in an inflammation-mediated increase in intestinal permeability.…”