Gestational Hypoglycaemia Restricts Foetal Growth and Skeletal Ossification in the Rat

Abstract

Maternal blood glucose level during gestation is crucial for normal foetal development. In the non- clinical studies in non-diabetic rats required by authorities, long-acting insulin analogous being developed to decrease blood glucose levels persistently generate safety data on embryo-foetal effects, which may be challenging to interpret. Separating potential toxicological effects of the insulin analogue from those caused by the hypoglycaemia becomes problematic, when the effects of the latter are unknown. Therefore, the aim of the present study was to investigate foetal effects of persistent maternal hypoglycaemia in rats after continuous maternal insulin-infusion throughout gestation. Effects on foetal size were measured and foetal skeletons were examined after alizarin red and alcian blue staining. Foetal hepatic glycogen content and foetal exposure to exogenous, i.e. human insulin, as well as endogenous plasma insulin levels were measured. Persistently 50% lowering maternal blood glucose throughout gestation caused a 10% decrease of foetal blood glucose levels on GD 20 and decreased foetal growth and development. Generalised decreased ossification and skeletal malformations of ribs, cranial bones, and long bones were seen with high incidences in foetuses. Furthermore, foetal but not maternal hepatic glycogen stores were decreased up to 50%. Foetuses were hypoinsulinaemic, and had no detectable exposure to exogenous insulin. The results indicate the existence of mechanisms which down-regulate placental glucose transfer to the foetus and consequently affect the foetal glucose metabolism and development reflected by counter-regulatory mobilisation of hepatic glycogen, decreased growth and delayed ossification of the skeleton as well skeleton malformations. As the foetuses were hypoinsulinaemic, these changes were most likely secondary to the maternal hypoglycaemia leading to foetal hypoglycaemia, and delayed development. This study provides novel data, which will aid the interpretation of findings in safety studies with longer-acting insulin analogues allowing differentiation between foetal effects of toxicological origin and those due to the persistent hypoglycaemia.