Effect of thyroxine supplementation on glomerular filtration rate in hypothyroid dogs

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Gommeren K, van Hoek I, Lefebvre HP, et al.

Journal of veterinary internal medicine / American College of Veterinary Internal Medicine 2009;23:844-849.

BACKGROUND: Glomerular filtration rate (GFR) is decreased in humans with hypothyroidism, but information about kidney function in dogs with hypothyroidism is lacking. HYPOTHESIS: Hypothyroidism influences GFR in dogs. The objective of this study was to assess GFR in hypothyroid dogs before implementation of thyroxine supplementation and after re-establishing euthyroidism. ANIMALS: Fourteen hypothyroid dogs without abnormalities on renal ultrasound examination or urinalysis. METHODS: Blood pressure and GFR (measured by exogenous creatinine clearance) were measured before treatment (T0, n=14) and at 1 month (T1, n=14) and at 6 months (T6, n=11) after beginning levothyroxine supplementation therapy (20 microg/kg/d, PO). The response to therapy was monitored at T1 by measuring serum total thyroxine and thyroid stimulating hormone concentrations. If needed, levothyroxine dosage was adjusted and reassessed after 1 month. Statistical analysis was performed using a general linear model. Results are expressed as mean+/-standard deviation. RESULTS: At T0, the average age of dogs in the study group was 6.3+/-1.4 years. Their average body weight decreased from 35+/-18 kg at T0 to 27+/-14 kg at T6 (P<.05). All dogs remained normotensive throughout the study. GFR increased significantly with levothyroxine supplementation; the corresponding results were 1.6+/-0.4 mL/min/kg at T0, 2.1+/-0.4 at T1, and 2.0+/-0.4 at T6 (P<.01). CONCLUSION: GFR was <2 mL/min/kg in untreated hypothyroid dogs. Re-establishment of a euthyroid state increased GFR significantly.