Equine Veterinary Journal Early View February 2016
By Heather Ferguson
Effects of maternal dexamethasone treatment on pancreatic β cell function in the pregnant mare and post natal foal
Valenzuela, O.A., Jellyman, J.K., Allen, V.L., Holdstock, N.B. and Fowden, A.L.
To investigate the effects on the metabolism (in particular glucose regulation) of pregnant mares and their offspring, intramuscular dexamethasone (200 µg/kg bwt) was administered to 6 pregnant mares on 3 occasions at 48 hour intervals. Five pregnant mares were injected at the same intervals with saline. Serial intravenous glucose tolerance tests were performed on all horses, 48 hours before the first dexamethasone/saline treatment, 24 hours after the second treatment, and 72 hours after the final treatment.
Baseline plasma concentrations of glucose, insulin and lactate were similar in both treatment and control groups. Within 3 days of treatment commencing, concentrations were significantly higher in the dexamethasone group than in the control group. Post-treatment, there was no difference in glucose or lactate concentrations but plasma insulin remained significantly higher in the treated group. The maximal glucose concentrations following dexamethasone treatment were not significantly different between the two groups; however, the magnitude of the insulin response to glucose was significantly higher in the dexamethasone treated group and the insulin response was more prolonged, indicating a greater pancreatic β cell response to exogenous glucose.
All foals were delivered uneventfully and when mature. Femur length and placental area were significantly lower in the dexamethasone treated group compared with the controls. There was no difference in growth rate of foals up to 12 weeks or plasma cortisol concentrations between treatment groups. The foals’ pancreatic β cell response to glucose was unaffected by maternal dexamethasone treatment with no difference between groups; however, there was a difference in the response to arginine, with a significantly lower insulin response in the dexamethasone group foals compared with the control group at 12 weeks old. This suggests maternal dexamethasone treatment suppresses the ability of insulin to stimulate uptake of amino acids.
Maternal treatment with dexamethasone during pregnancy affects glucose and insulin regulation in the mare, results in lower placental size but does not significantly alter foal growth after birth. It does not significantly alter glucose and insulin metabolism in the foal but does reduce amino acid uptake.