The effects of high-sucrose diets and of maternal diabetes on the ultrastructure of the visceral yolk sac endoderm in rat embryos developing in vivo and in vitro.

The ultrastructure of the visceral yolk sac endoderm of in vivo developing 9- to 13-day-old embryos from 2 diabetic rat models (streptozotocin diabetes and Cohen--genetically determined--diabetes) and from nondiabetic rats fed high sucrose diets have been studied. This was compared to yolk sacs from 9.5-day-old embryos cultured for 48 h in sera from diabetic and nondiabetic rats fed a high-sucrose diet. Light-microscopic, TEM and SEM studies showed that the pathological cellular changes in the visceral yolk sac endoderm from diabetic rats were first observed on day 9 and were most severe among 11-day-old embryos. In vitro culture of control rat embryos in serum from experimental animals induced a reduction in the number of microvilli, of vacuolar intracellular inclusions and an increase in the number of degenerated endodermal cells. SEM studies showed that in addition to disappearance of microvilli, the majority of cells were collapsed and had degenerated cell membranes. Culture of embryos from diabetic animals in control serum only slightly reversed the pathological changes in the visceral yolk sac endoderm. A good correlation exists between the rate of embryonic malformations in diabetic rats and an index of endodermal-cell damage in the visceral yolk sac.