Offspring from mothers with diabetes mellitus are at risk of altered calcium homeostasis and bone mineral metabolism. Using the streptozotocin rat model of diabetic pregnancy we have previously shown that diabetic mothers show marked hypercalciuria (Birdsey et al. 1995). We have also shown that the adult offspring of these rats have, by constrast, reduced urinary calcium output and a remodelling of bone (Hamilton et al. 1999). Previous work has also shown altered calbindin-D28K mRNA in kidneys of pregnant diabetic rats and adult offspring from diabetic mothers (Hamilton et al. 2000). The aim of this study was to establish whether reduced urinary calcium output was associated with a change in protein expression of calbindin-D28K and PMCA in neonatal offspring of diabetic rats.
Two rat groups were studied: offspring born to control mothers (OC) and offspring born to streptozotocin-induced diabetic mothers (OD). Urine samples were collected following 2 h incubation from neonates and every 24 h over a 3 day period from 8-, 12- and 16-week-old rats. Urinary calcium output was measured using atomic absorption spectrophotometry and expressed as µmol 24 h-1 g-1 (mean ± S.E.M., n = number of litters); see Table 1. Calbindin-D28K and PMCA protein expression was measured in neonate kidneys using Western blotting and signal was measured in arbitrary density units, normalised to a single standard sample and expressed as a percentage (mean ± S.E.M., n = number of litters).
Reduced urinary calcium output was observed in OD when compared with OC in neonates, and 8-, 12- and 16-week rats. Calbindin-D28K (OC = 12.9 ± 2.2 % vs. OD = 65.9 ± 11.9 %, n = 6, P < 0.01, ANOVA) and PMCA (OC = 101.2 ± 4.5 % vs. OD = 153.4 ± 8.4 %, n = 6, P < 0.001, ANOVA) protein expression was significantly higher in neonatal OD than neonatal OC.
In conclusion, these data provide support for previous evidence suggesting that diabetic pregnancy leads to reduced calcium output in offspring and indicate that increased calbindin-D28K and PMCA expression may be partly responsible for this altered renal calcium homeostasis in rats.
This work was supported by the Sir Jules Thorn Charitable Trust.
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