Abstract
Observations on 125I-insulin degradation by human placental membranes obtained from mature and immature placentae of normal pregnant women, have shown that such degradationdepends on the incubation time, temperature and membrane concentration.
This paper compares the 125I-insulin degradation by placental membranes of pregnant diabetics with that of normal pregnant women.
Placentae from 12 pregnant diabetics were obtained from deliveries at 38-40 weeksof gestation. One diabetic was treated by diet alone and the others with insulin throughout pregnancy. Control during pregnancy was good.
Placental membranes of 100, 000 g pellets were prepared by Posner's method, and membranes washed twice were used. The degradation experiments were carried out according tothe previously described method, using rebinding, TCA precipitability, immunoreactivity and gel-chromatography.
Placental membranes from normal pregnant women, and incubation of 125I-insulin without membranes, were utilized as controls.
The 125I-insulin degradation by diabetic placental membranes was found to be muchgreater than that by non-diabetic membranes. In diabetics, the mean 125I-insulin degradation rate was 21.7% at 5 min incubation, 53% at 40 min and 70% at 90 min, whereas in normal pregnant women, it was 8.7% at 5 min, 34.3% at 40 min and 48. 2% at 90 min. Significant differences were apparent at each incubation time between the membranes of normal pregnant women and those of pregnant diabetics. No significant differences in degradation were found between normal pregnant women and one diabetic with an intrauterine death.
It is suggested therefore that degradation systems may play a role in the regulation of insulin concentration in placental tissues.
It remains unknown, however, why the degradation in diabetics should be larger than that in non-diabetics. Further studies along these lines are clearly required.
