The objective of this study was to determine the effects of hypothyroidism on insulin sensitivity, glucose tolerance, and concentrations of hormones counter-regulatory to insulin in eight anestrous mixed-breed dogs with experimentally induced hypothyroidism and eight euthyroid control dogs. Insulin-modified frequently sampled IV glucose tolerance test and minimal model analysis were used to determine basal plasma insulin and glucose concentrations, acute insulin response to glucose, insulin sensitivity, glucose effectiveness and disposition index.

Insulin sensitivity was lower in the hypothyroid group than in the euthyroid group, whereas acute insulin response to glucose was higher. Glucose effectiveness and disposition index were not different between groups. Basal serum growth hormone (GH) and insulin-like growth factor-1 (IGF-1) concentrations as well as abdominal fat content were high in hypothyroid dogs, but urine cortisol-to-creatinine concentration ratios were unchanged.

Hypothyroidism appeared to negatively affect glucose homeostasis by inducing insulin resistance, but overall glucose tolerance was maintained by increased insulin secretion in hypothyroid dogs. Possible factors affecting insulin sensitivity are high serum GH and IGF-1 concentrations and an increase in abdominal fat. In dogs with diseases involving impaired insulin secretion such as diabetes mellitus, concurrent hypothyroidism can have important clinical implications.

Source : N. Hofer-Inteeworn et al., 2012. Effect of hypothyroidism on insulin sensitivity and glucose tolerance in dogs. AJVR 73: 529-538. doi: 10.2460/ajvr.73.4.529