The Effect of Interday Variation and a Short-Term Stressor on Insulin Sensitivity in Clinically Normal Cats

Abstract

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 (SI) averaged 2.9 ± 0.4 × 10−4 min−1/μU/ml (range 1.9–4.6 × 10−4 min−1/μU/ml), with a mean interday coefficient of variation (CV) of 35.4 ± 6.4% (range 12.8–58.5%). Glucose effectiveness (SG) 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 × 10−4 min−1/μU/ml (range 1.6–7.3 × 10−4 min−1/μU/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.