THE EFFECT OF DIABETES-MELLITUS ON URINARY CALCIUM EXCRETION IN PREGNANT RATS AND THEIR OFFSPRING

The effect of maternal diabetes mellitus on renal calcium excretion in pregnant rats and their offspring has been examined in order to ascertain the role of the kidney in the disturbed calcium homeostasis of infants born to diabetic mothers. Diabetic pregnant (DP) rats exhibited severe hypercalciuria which greatly exceeded the urinary calcium losses (UCaV) in non-diabetic pregnant (CP) or nonpregnant diabetic (D) rats. Means+/-S.E.M. for UCaV at day 21 (mmo1/24h) were: DP=1.12+/-0.09 (n=7); CP=0.06+/-0.01 (n=7); D=0.63+/-0.06 (n=7) (P<0.001 DP vs CP and DP vs D). The profile for urinary calcium excretion in the three groups was different from that of other measured ions. The degree of natriuresis, for example, was comparable in DP and D rats at all stages studied. Although magnesium output was significantly greater in DP than D rats on days 14 and 21, this appeared to result from an additive effect of the magnesiuresis seen when pregnancy and diabetes were studied separately. The marked renal calcium wasting of diabetic pregnancy will have implications for overall calcium balance in the mother. For example, an enhanced intestinal calcium absorption was seen in DP rats in the second half of gestation. Meansz=/-S.E.M. for day 21 (mmol/24 h) were: DP=38+/-0.8 (n=7); CP=1.4+/-0.3 (n=7); D=1.6+/-0.3 (n=7) (P<0.05 DP vs CP and DP vs D). The hypercalciuria may also contribute to the disturbed calcium homeostasis of the neonate if it reduces the amount of calcium available for transfer to the fetus. In contrast to their mothers, the offspring of DP rats did not show a raised UCaV compared with CP pups Means+/-S.E.M. at day 1 postpartum (nmol/2 h per pup) were: DP=47.2+/-15.7 (n=4 litters); CP=72.2+/-14.1 (n=7 litters) (not significant). Changes in neonatal renal function are therefore unlikely to contribute to their disturbed calcium balance. In fact, their slightly reduced urinary calcium output may be an attempt to compensate for their lowered total body calcium as reported elsewhere.