Sympathoadrenal and other endocrine and metabolic responses to hypoglycaemia in the fetal foal during late gestation.

This research explores how low blood sugar (hypoglycemia) affects hormonal and metabolic responses in unborn foals (baby horses) during the late stages of pregnancy. Significant differences were found between foals that were near to birth and those at least two weeks away, notably in their levels of cortisol and adrenaline-like hormones.

Study Methodology

• The researchers conducted ten insulin challenge tests on nine chronically catheterized fetal foals between 253 and 314 days of gestation.
• Insulin, a hormone that lowers blood sugar levels, was injected into the fetuses, and subsequent changes in several bodily parameters were measured before and after the injection.
• These included changes in blood levels of glucose, catecholamines (adrenaline-like hormones), cortisol (a stress hormone), ACTH (a hormone that regulates cortisol), free fatty acids and lactate (a product of metabolism).
• Other parameters measured included the foals’ blood gases, pH, hemoglobin levels, and heart rate throughout a 2-3 hour experimental period.

Important Findings

• After insulin administration, all fetal foals experienced a 50% fall in blood glucose levels (meaning they became hypoglycemic), among other changes.
• However, differences were observed between foals closer to term (referred to as group 2) and those at least two weeks away from being born (group 1).
• Foals in group 2, being closer to delivery, had significantly higher levels of cortisol and catecholamines when compared with group 1.
• Response to insulin was also different: Group 2 showed greater increases in catecholamine levels compared with group 1, and only group 2 had increased cortisol levels following insulin injection.
• Insulin injection also led to conditions of acidosis (high blood acidity), increased heart rate, and elevated levels of lactate and free fatty acids in all fetuses.

Conclusions and Implications

• From these findings, it can be inferred that hypoglycemia triggers the activation of the sympathoadrenal system, which helps the body respond to stress, in foals from 75% of the gestation period.
• However, the response of the pituitary-adrenocortical axis, another part of the body’s stress response system, does not show much reaction to low blood sugar levels until the fetus is much closer to their birth term.
• This research is fundamental in understanding the hormonal and metabolic changes that fetal horses undergo during the late gestation period, and it could have implications in managing the health of pregnant mares and their developing foals.