The effect of interday variation and a short-term stressor on insulin sensitivity in clinically normal cats

To determine whether there is a day-to-day variation in insulin sensitivity in cats, we subjected six clinically normal cats to four insulin-modified frequently sampled intravenous glucose tolerance tests (FSIVGTTs) over 7 days. The insulin-modified FSIVGTTs were analysed by the minimal model method. Minimal model insulin sensitivity (S(I)) averaged 2.9+/-0.4 x 10(-4) min(-1)/microU/ml (range 1.9-4.6 x 10(-4) min(-1)/microU/ml), with a mean interday coefficient of variation (CV) of 35.4+/-6.4% (range 12.8-58.5%). Glucose effectiveness (S(G)) averaged 0.029+/-0.002 min(-1)(range 0.024-0.037 min(-1)), and showed less interday variability with a mean CV of 24.7+/-4.3% (range 7.9-39.3%). Insulin sensitivity was also measured after a short-term stressor (5-min spray bath) of sufficient magnitude to elevate blood glucose levels. The mean insulin sensitivity after the stressor was 3.6+/-0.8 x 10(-4) min(-1)/microU/ml (range 1.6-7.3 x 10(-4) min(-1)/microU/ml), which was not significantly different to the mean insulin sensitivity before the short-term stressor (P=0.237). The mean glucose effectiveness after the stressor was 0.046+/-0.004 min(-1)(range 0.032-0.057 min(-1)), which was significantly different from mean glucose effectiveness before the short-term stressor (P=0.003). We conclude that insulin sensitivity is highly variable from day to day in normal cats, and that hyperglycaemia in response to short-term stressors is probably due to increased hepatic glucose production, rather than peripheral insulin resistance.