Effect of experimental hypothyroidism on glomerular filtration rate and plasma creatinine concentration in dogs

Abstract

Background: Hypothyroidism affects renal function in a manner opposite the effects of hyperthyroidism. Objective: To evaluate the effects of experimentally induced hypothyroidism on glomerular filtration rate (GFR) and basal plasma creatinine concentration in dogs. Animals: Sixteen anestrous, female dogs. Methods: Hypothyroidism was induced by administration of 131I in 8 dogs, and 8 healthy euthyroid dogs acted as controls. Exogenous plasma creatinine clearance (an estimate of GFR) was measured in all dogs before (control period) and 43-50 weeks after induction of hypothyroidism (posttreatment period). Other pharmacokinetic parameters of creatinine were also determined. Results: No significant difference was observed for basal plasma creatinine concentration and creatinine clearance between control and hypothyroid dogs in the control period. In the posttreatment period, mean ± SD creatinine clearance in the hypothyroid group (2.13 ± 0.48 mL/min/kg) was lower (P < 0.001) than that of the control group (3.20 ± 0.42mL/kg/min). Nevertheless, basal plasma creatinine concentrations were not significantly different between the hypothyroid and control groups (0.74 ± 0.18 versus 0.70 ± 0.08mg/dL, respectively) because endogenous production of creatinine was decreased in hypothyroid dogs (22 ± 3 versus 32 ± 5mg/kg/d, P=.001). Conclusion and Clinical Importance: Hypothyroidism causes a substantial decrease in GFR without altering plasma creatinine concentrations, indicating that GFR evaluation is needed to identify renal dysfunction in such patients. © 2009 by the American College of Veterinary Internal Medicine.