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 ascer tain the role of the kidney in the disturbed calcium homeostasis of in fants born to diabetic mothers. Diabetic pregnant (DP) rats exhibited severe hypercalciuria which greatly exceeded the urinary calcium losse s (UCaV) in non-diabetic pregnant (CP) or nonpregnant diabetic (D) rat s. 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 group s was different from that of other measured ions. The degree of natriu resis, for example, was comparable in DP and D rats at all stages stud ied. Although magnesium output was significantly greater in DP than D rats on days 14 and 21, this appeared to result from an additive effec t of the magnesiuresis seen when pregnancy and diabetes were studied s eparately. The marked renal calcium wasting of diabetic pregnancy will have implications for overall calcium balance in the mother. For exam ple, 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) w ere: 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 d isturbed calcium homeostasis of the neonate if it reduces the amount o f calcium available for transfer to the fetus. In contrast to their mo thers, the offspring of DP rats did not show a raised UCaV compared wi th 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 signi ficant). 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 th eir lowered total body calcium as reported elsewhere.