Effects of diabetes and food deprivation on shivering activity during progressive hypothermia in the rat.

Diabetes mellitus and food deprivation are two conditions known to significantly reduce the ability to generate body heat during periods of acute cold stress. The purpose of this study was to determine if shivering is attenuated in the urethane-anesthetized (1.5 g/kg; i.p.), streptozotocin-induced diabetic (STZ; n = 10) and food-deprived (12-hour nocturnal fast) rat (FD; n = 11) as colonic temperature (Tcol) declined from baseline (36 degrees C) to 28 degrees C. Shivering was assessed using the mean rectified electromyographic (EMG) signal obtained from indwelling bipolar electrodes placed in the gluteus superficialis muscle. Although the mean rectified EMG progressively increased (P < or = 0.05) between Tcol of 33 degrees C to 28 degrees C and achieved peak activity (7.89 +/- 1.80 microV) at 29 degrees C in non-diabetic rats, shivering activity was virtually absent in the STZ group throughout cooling (e.g. peak EMG = 0.49 +/- 0.09 microV). The lack of shivering activity in STZ could partially explain the shorter time to reach 28 degrees C (STZ, 48.5 +/- 1.5 vs CON, 136.5 +/- 23.0 min; P < or = 0.05) and the divergent trends in oxygen consumption (delta VO2) between STZ and non-diabetic rats. In the FD group, the mean peak rectified EMG activity (3.09 +/- 1.35 microV) was significantly lower (P < or = 0.05) than the fed group. The peak delta VO2 from baseline (FD, +2.11 +/- 0.36 vs. CON, +4.51 +/- 0.50 mlO2/min) and the time taken to reach 28 degrees C (FD, 73.4 +/- 4.2 vs CON, 136.5 +/- 23.0 min) were statistically different (P < or = 0.05) between groups. The results indicate that: 1) shivering thermogenesis is severely depressed and hypothermia accelerated in experimental diabetic animals as evidenced by the attenuation in mean rectified EMG and delta VO2, and 2) FD rats experienced a faster decline in colonic temperature than the fed group due, in part, to the relatively greater decline in shivering activity and oxygen consumption.