Raised Plasma Somatomedin Activity and Cartilage Metabolic Activity (35S Sulphate Uptake in Vitro) in the Fetus of the Mildly Diabetic Pregnant Rat

A mildly diabetic state was induced in pregnant rats following treatment with streptozotocin the day after mating. On day 21 of gestation, these rats had a lower plasma insulin (55 +/- 9 versus 107 +/- 23 mU/l for control rats; p less than 0.05, mean +/- SEM) and a reduced pancreatic area occupied by insulin-containing cells compared with control animals (0.40 +/- 0.04 versus 1.03 +/- 0.08%; p less than 0.001), but hyperglycaemia was not apparent. Fetuses from mildly diabetic animals were longer but not heavier than those from control rats. Plasma somatomedin activity measured by fetal rat cartilage bioassay was higher in fetuses from mildly diabetic rats (1.12 +/- 0.07 versus: 0.74 +/- 0.05 U/ml for control fetuses; p less than 0.001) as was cartilage metabolic activity in basal culture medium (35S sulphate uptake) (1883 +/- 141 versus 1473 +/- 104 c.p.m./mg for control rats; p less than 0.05), but plasma insulin levels and the pancreatic area occupied by insulin-containing cells did not differ between the two groups of fetuses. Fetal plasma somatomedin activity, measured by fetal cartilage assay, showed a significant positive correlation with both body weight and length. It is concluded that by day 21 of gestation a small body overgrowth had occurred in the fetus of the mildly diabetic rat and this was associated with an increase in plasma somatomedin activity, but not with any abnormality of circulating insulin levels or volume density of B cells in the pancreatic islets.