Effects of Bromocriptine on Glucose and Insulin Dynamics in Normal and Insulin Dysregulated Horses.
Abstract: The objectives of the study were to study the effects of the synthetic ergot alkaloid (EA), bromocriptine, on glucose and lipid metabolism in insulin dysregulated (ID, n = 7) and non-ID (n = 8) mares. Horses were individually housed and fed timothy grass hay and two daily concentrate meals so that the total diet provided 120% of daily DE requirements for maintenance. All horses were given intramuscular bromocriptine injections (0.1 mg/kg BW) every 3 days for 14 days. Before and after 14 days of treatment horses underwent a combined glucose-insulin tolerance test (CGIT) to assess insulin sensitivity and a feed challenge (1 g starch/kg BW from whole oats) to evaluate postprandial glycemic and insulinemic responses. ID horses had higher basal plasma concentrations of insulin (P = 0.01) and triglycerides (P = 0.02), and lower concentrations of adiponectin (P = 0.05) compared with non-ID horses. The CGIT response curve showed that ID horses had slower glucose clearance rates (P = 0.02) resulting in a longer time in positive phase (P = 0.03) and had higher insulin concentrations at 75 min (P = 0.0002) compared with non-ID horses. Glucose (P = 0.02) and insulin (P = 0.04) responses to the feeding challenge were lower in non-ID compared to ID horses. Regardless of insulin status, bromocriptine administration increased hay intake (P = 0.03) and decreased grain (P < 0.0001) and total DE (P = 0.0002) intake. Bromocriptine treatment decreased plasma prolactin (P = 0.0002) and cholesterol (P = 0.10) and increased (P = 0.02) adiponectin concentrations in all horses. Moreover, in both groups of horses, bromocriptine decreased glucose clearance rates (P = 0.02), increased time in positive phase (P = 0.04) of the CGIT and increased insulin concentrations at 75 min (P = 0.001). The postprandial glycemic (P = 0.01) and insulinemic (P = 0.001) response following the oats meal was lower after bromocriptine treatment in all horses. In conclusion, in contrast to data in humans and rodents, bromocriptine treatment reduced insulin sensitivity in all horses, regardless of their insulin status. These results indicate that the physiological effects of EA might be different in horses compared to other species. Moreover, because bromocriptine shares a high degree of homology with natural EA, further investigation is warranted in horses grazing endophyte-infected grasses.
Copyright © 2022 Loos, Urschel, Vanzant, Oberhaus, Bohannan, Klotz and McLeod.
Publication Date: 2022-05-31 PubMed ID: 35711802PubMed Central: PMC9194999DOI: 10.3389/fvets.2022.889888Google Scholar: Lookup
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Summary
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The research study examines the impact of bromocriptine, a synthetic ergot alkaloid, on the metabolism of glucose and the hormone insulin in both normal horses and those with insulin dysregulation, showing that this substance may decrease insulin sensitivity in horses.
Experiment Design
- The research involved two groups of mares: insulin dysregulated (ID) and non-ID, each group comprising seven and eight horses respectively.
- All horses were housed individually and fed timothy grass hay and two concentrate meals daily, altogether providing 120% of daily digestible energy (DE) requirements for maintenance.
- These horses were treated with intramuscular bromocriptine injections (0.1 mg/kg body weight) once every 3 days over two weeks.
- A combined glucose-insulin tolerance test (CGIT) was performed before and after the 14-day treatment period to measure insulin sensitivity.
- A feed challenge was conducted to evaluate both glycemic and insulinemic responses in horses post meal, which consisted of 1g of starch/kg body weight from whole oats.
Findings
- Compared to non-ID horses, ID horses exhibited higher baseline levels of insulin and triglycerides, but lower concentrations of the protein hormone adiponectin.
- The CGIT results revealed slower glucose clearance rates in ID horses, which resulted in more time in the positive phase and higher insulin levels at the 75-minute mark in comparison to the non-ID horses.
- The non-ID horses had lower glucose and insulin responses to the feed challenge than the ID horses did.
- Bromocriptine treatment led to all horses, regardless of insulin status, showing an increase in hay intake, a decrease in grain and total DE intake, and a decrease in plasma prolactin and cholesterol levels. Their adiponectin concentrations also increased.
- Following the bromocriptine treatment, both groups of horses displayed decreased glucose clearance rates and increased insulin levels at the 75-minute mark. This result illustrates reduced insulin sensitivity brought on by bromocriptine treatment. Additionally, after feeding, the horses also displayed a lower postprandial glycemic and insulinemic response.
Conclusion
- In contrast to data from human and rodent studies, the study found that bromocriptine reduced insulin sensitivity in all horses, regardless of their insulin status, indicating that the effects of ergot alkaloids might differ in horses compared to other species.
- Further research is recommended, especially on horses grazing on grasses infected with endophyte fungi. This recommendation stems from the fact that bromocriptine shares a high degree of similarity with natural ergot alkaloids, compounds that these fungi produce.
Cite This Article
APA
Loos CMM, Urschel KL, Vanzant ES, Oberhaus EL, Bohannan AD, Klotz JL, McLeod KR.
(2022).
Effects of Bromocriptine on Glucose and Insulin Dynamics in Normal and Insulin Dysregulated Horses.
Front Vet Sci, 9, 889888.
https://doi.org/10.3389/fvets.2022.889888 Publication
Researcher Affiliations
- Department of Animal and Food Sciences, University of Kentucky, Lexington, KY, United States.
- Department of Animal and Food Sciences, University of Kentucky, Lexington, KY, United States.
- Department of Animal and Food Sciences, University of Kentucky, Lexington, KY, United States.
- School of Animal Sciences, Louisiana State University, Baton Rouge, LA, United States.
- Department of Animal and Food Sciences, University of Kentucky, Lexington, KY, United States.
- Forage-Animal Production Research Unit, Agricultural Research Service, United States Department of Agriculture, Lexington, KY, United States.
- Department of Animal and Food Sciences, University of Kentucky, Lexington, KY, United States.
Conflict of Interest Statement
The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
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