Sympathoadrenal and other endocrine and metabolic responses to hypoglycaemia in the fetal foal during late gestation.
Abstract: In the present study, ten insulin challenge tests were carried out on nine chronically catheterized fetal foals between 253 and 314 days gestation (term > 320 days). Changes in fetal plasma concentrations of glucose, catecholamines, cortisol, ACTH, free fatty acid (FFA) and lactate were measured before and after a bolus dose of insulin (0.5-2.0 u/kg I.V.). Fetal blood gases, pH, haemoglobin levels and heart rate were measured throughout the 2-3h experimental period. The fetuses fell into two distinct groups on the basis of proximity to delivery and basal plasma cortisol and catecholamine levels. Those within 2-10 days of delivery after 300 days (group 2, number of experiments (n) = 4) had plasma cortisol and noradrenaline concentrations which were significantly higher (P < 0.05) than the corresponding values in fetuses sampled earlier in gestation or at least 2 weeks before foaling (group 1, n = 6). Although insulin administration resulted in a 50% fall in plasma glucose in all animals, group 2 showed significantly greater increases in plasma noradrenaline than group 1. In neither group were there detectable changes in plasma adrenaline. In group 2, increases in plasma cortisol were seen following insulin, whereas no cortisol changes were observed in group 1, despite rises in plasma ACTH. Insulin administration also led to acidosis and increases in heart rate and plasma lactate and FFA levels in all fetuses studied. However, only group 2 became consistently hypoxic during the insulin challenge. No significant changes in plasma glucose or any of the other parameters were observed in the fetuses after saline administration (n = 5). These findings suggest that hypoglycaemia activates the sympathoadrenal system in the fetal foal from 75% of gestation but has relatively little effect on the fetal pituitary-adrenocortical axis until much closer to term.
Publication Date: 1995-07-01 PubMed ID: 7576604DOI: 10.1113/expphysiol.1995.sp003875Google Scholar: Lookup
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- Journal Article
- Research Support
- Non-U.S. Gov't
Summary
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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.
Cite This Article
APA
Silver M, Fowden AL.
(1995).
Sympathoadrenal and other endocrine and metabolic responses to hypoglycaemia in the fetal foal during late gestation.
Exp Physiol, 80(4), 651-662.
https://doi.org/10.1113/expphysiol.1995.sp003875 Publication
Researcher Affiliations
- Physiological Laboratory, Cambridge, UK.
MeSH Terms
- Adrenal Glands / embryology
- Animals
- Blood Glucose / analysis
- Endocrine Glands / embryology
- Fetal Diseases / chemically induced
- Fetal Diseases / physiopathology
- Fetus / physiology
- Gestational Age
- Hormones / blood
- Horses / embryology
- Hypoglycemia / blood
- Hypoglycemia / chemically induced
- Hypoglycemia / physiopathology
- Insulin
- Sympathetic Nervous System / embryology
Citations
This article has been cited 3 times.- Hallman I, Karikoski N, Kareskoski M. The effects of obesity and insulin dysregulation on mare reproduction, pregnancy, and foal health: a review. Front Vet Sci 2023;10:1180622.
- Rozance PJ, Limesand SW, Barry JS, Brown LD, Thorn SR, LoTurco D, Regnault TR, Friedman JE, Hay WW Jr. Chronic late-gestation hypoglycemia upregulates hepatic PEPCK associated with increased PGC1alpha mRNA and phosphorylated CREB in fetal sheep. Am J Physiol Endocrinol Metab 2008 Feb;294(2):E365-70.
- Giussani DA, Forhead AJ, Fowden AL. Development of cardiovascular function in the horse fetus. J Physiol 2005 Jun 15;565(Pt 3):1019-30.
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