Evaluating insulindysregulation in horses: A two-step insulin-tolerance test using porcine zinc insulin.

The research article conducts a comparative study on the effectiveness of porcine zinc insulin against human insulin when used in insulin-tolerance tests for diagnosing insulin resistance in horses.

Research Background and Objectives

• In horses, a condition known as insulin dysregulation is characterized by high levels of insulin in blood circulation, a state known as hyperinsulinemia, and peripheral insulin resistance. An insulin-tolerance test is used to diagnose insulin resistance in horses. In an insulin-sensitive horse, administration of 0.1 IU/kg body weight of recombinant regular human insulin should cause a 50% reduction in blood glucose concentration 30 minutes after insulin injection.
• The porcine zinc insulin is veterinary-approved and therefore more accessible to practitioners than the human insulin. The research aims to compare glucose and insulin dynamics during a standard insulin-tolerance test using human insulin as against porcine zinc insulin.

Research Methodology

• Twelve Icelandic horses were subjected to insulin-tolerance test with both recombinant regular human insulin (ITT-RHI) and porcine zinc insulin (ITT-PZI). Both dosages were administered in a randomised crossover design, meaning that the order of substances administered was randomized.
• The effects on insulin and glucose dynamics from each of the tests were compared. In addition, the consistency of categorization into insulin-sensitive and insulin-resistant groups was also evaluated after each test.
• No complications were reported with the use of either RHI or PZI have been reported during the ITT.

Research Findings

• The results of both tests showed a strong correlation, which was statistically significant.
• There were no statistically significant differences between the two tests in terms of blood glucose concentrations and the percentage reduction in glucose concentration.
• However, the number of horses classified as insulin resistant varied, with four out of twelve horses categorized as insulin resistant with the ITT-RHI against seven out of twelve horses under the ITT-PZI.
• An interesting revelation of the study was that the test’s performance improved, based on the Youden index, when a cut-off value of 40% blood glucose reduction was used for the ITT-PZI test, instead of the standard 50% used for RHI.

Conclusion

• Considering the seemingly weaker effect of PZI and with the adjusted cut-off value, PZI can be an appropriate substitute to RHI in an insulin-tolerance test. This finding is valuable as it underscores the potential of using porcine zinc insulin in place of human insulin for testing insulin resistance in horses, and thus increasing accessibility to this diagnostic tool.