Effects of Bromocriptine on Glucose and Insulin Dynamics in Normal and Insulin Dysregulated Horses.
Authors: Loos Caroline M M, Urschel Kristine L, Vanzant Eric S, Oberhaus Erin L, Bohannan Adam D, Klotz James L, McLeod Kyle R
Journal: Frontiers in veterinary science
Summary
# Editorial Summary: Bromocriptine's Unexpected Effects on Equine Glucose Metabolism Ergot alkaloids present a significant concern for horses grazing endophyte-infected pastures, yet their metabolic consequences remain poorly understood. Loos and colleagues investigated whether bromocriptine—a synthetic ergot alkaloid—could improve insulin sensitivity in 15 mares (seven insulin dysregulated, eight metabolically normal), administering intramuscular injections of 0.1 mg/kg bodyweight every three days for a fortnight whilst monitoring glucose clearance via combined glucose-insulin tolerance testing and postprandial responses to oat challenge meals. Contrary to findings in humans and rodents, bromocriptine paradoxically impaired insulin sensitivity across both groups: glucose clearance rates slowed significantly (P = 0.02), time spent in positive glucose phase lengthened (P = 0.04), and insulin concentrations at 75 minutes increased substantially (P = 0.001), whilst interestingly, immediate postprandial responses to the oat meal actually decreased post-treatment. The practical implications are substantial—grazing horses on endophyte-infected pastures may experience ergot alkaloid-induced deterioration in insulin dynamics independent of baseline metabolic status, potentially accelerating insulin dysregulation in predisposed individuals and warranting urgent investigation into whether chronic natural ergot alkaloid exposure contributes to field cases of equine metabolic syndrome.
Read the full abstract on PubMed
Practical Takeaways
- •Ergot alkaloid exposure (via bromocriptine or endophyte-infected pastures) appears to worsen insulin sensitivity in horses and should be avoided, particularly in horses already prone to insulin dysregulation or metabolic syndrome
- •Use caution interpreting ergot alkaloid effects based on research from other species—equine metabolic responses differ significantly from humans and rodents, making direct translation of treatments inappropriate
- •Monitor pasture quality and avoid endophyte-infected fescue and other toxic grasses, especially for metabolically compromised horses, as natural ergot alkaloids share structural similarity with the detrimental effects seen here
Key Findings
- •Bromocriptine decreased insulin sensitivity in all horses (both ID and non-ID), contrary to effects observed in humans and rodents, with slower glucose clearance rates (P=0.02) and higher insulin concentrations at 75 min (P=0.001)
- •ID horses demonstrated baseline metabolic dysfunction with higher basal insulin (P=0.01), higher triglycerides (P=0.02), and lower adiponectin (P=0.05) compared to non-ID horses
- •Bromocriptine altered feeding behaviour in all horses, increasing hay intake (P=0.03) while significantly decreasing grain (P<0.0001) and total energy intake (P=0.0002)
- •Bromocriptine treatment increased adiponectin concentration (P=0.02) and decreased cholesterol (P=0.10) despite worsening insulin sensitivity, suggesting complex species-specific metabolic effects