Diabetic women are known to encounter more problems with pregnancy and labour than non-diabetic women. In particular they are more likely to require an emergency Caesarean delivery, even when their blood glucose is well controlled and their babies are of normal weight. This suggests that the myometrium of diabetics may be less able to contract well or over a prolonged time period compared to non-diabetics. However, very little is known about the intrinsic properties of myometrium from diabetic women, or the response to changes in glucose. We have therefore begun to compare in vitro contractility and Ca signalling between the two groups and examine the effects of glucose deprivation or hyperinsulaemia. Uterine biopsies were obtained at term with informed, ethical consent from diabetic and non-diabetic women have elective Caesareans, myometrial strips dissected, loaded with Indo-1 and force and Ca signalling simultaneously measured, at 37 oC. Under control conditions the frequency of Ca transients and contractions were less in diabetics, being 5.3+ 1.0 and in controls, 9.2+ 0.5 contractions/hour, n= 13 and 68 respectively. Contraction amplitude, relative to high-K contractions was also lower in the diabetics; 73% compared to non-diabetic controls. When the perfusate was changed from control (8 mM) to 0 glucose there was a marked variation in how long contractions were produced for between tissues in both groups, however those from diabetics were abolished faster (7.7+ 2.1 hours, n=6) than non-diabetics (11.9+2.7 hours, n=27) . Only 1 diabetic sample continued to contract after 12 hours in 0-glucose, whereas 10 controls did so, two of which continued to contract for over 2 days. When hyperinsulaemia was simulated by adding 700 pM insulin after control contractions had been established, little change occurred in diabetic samples (n=3) but a profound decrement in force amplitude (from 100 to 19+13 %, n=8) occurred in the non-diabetic samples and their frequency was also significantly reduced. Similar changes in Ca occurred. These preliminary findings suggest that there are differences in uterine contractility associated with diabetes, with them perhaps being less able to withstand the metabolic demands of labour, as blood flow and hence glucose falls with contraction. This may relate to differences in glycogen utilization. Insulin resistance in diabetic women may account for the reduced effects of hyperinsulaemia.