A NONLINEAR EFFECT OF AMBIENT-TEMPERATURE ON APPARENT GLUCOSE-TOLERANCE

Increased ambient temperature affects apparent oral glucose tolerance to an extent which may have clinical implications for the diagnosis of impaired glucose tolerance and gestational diabetes. As a first step in order to better define the nature of this effect, we have examined, in a climate chamber, the effects of ambient temperature at four leve ls (20, 25, 30, and 35 degrees C) on glucose and insulin responses to a standard 75 g oral glucose tolerance test in seven non-diabetic male subjects. Plasma glucose responses to ambient temperature were compar ed with the responses of core (auditory canal) and skin temperatures. The 2-h plasma glucose was affected in a nonlinear manner by ambient t emperature (5.4+/-0.2, 5.3+/-0.4, 6.5+/-0.3, 6.4+/-0.4 mmol/l at 20, 2 5, 30, and 35 degrees C, P = 0.015) with the effect localised between 25 and 30 degrees C (P = 0.012). Core temperature responded in a simil ar manner (36.6+/-0.1, 36.6+/-0.1, 36.9+/-0.1, 37.0+/-0.1 (P = 0.0005) with the effect localised between 25 and 30 degrees C (P = 0.011). Ho wever skin temperature increased significantly with each 5 degrees C i ncrease in ambient temperature (30.2+/-0.5, 33.0+/-0.5, 34.2+/-0.2, 35 .2+/-0.2, P less than or equal to 0.0001). We conclude that the acute effect of ambient temperature on apparent glucose tolerance is most li kely due to redistribution of blood flow between cutaneous and viscera l beds driven by changes in core temperature. The absence of temperatu re effects between the two lowest, and between the two highest tempera tures, provides workable guidelines for the standardisation of conditi ons during oral glucose tolerance tests in circumstances where tempera ture may have clinically significant effects. (C) 1997 Elsevier Scienc e Ireland Ltd.