Comparison of a modified 2-step insulin response test performed with porcine zinc insulin and an oral glucose test to detect hyperinsulinemic Icelandic horses.

This research evaluates two different methods of detecting insulin dysregulation in Icelandic horses – the Oral Glucose Test (OGT) and the modified 2-step Insulin Response Test (2-step IRT). The main aim of the study was to investigate if horses with hyperinsulinemia can also display signs of insulin resistance and can thus be identified by the 2-step IRT using porcine zinc insulin.

Research Background and Objective

• The two common methods used to detect insulin dysregulation in horses are oral and intravenous (IV) testing protocols. The former mainly focuses on insulin resistance (IR), while the latter assesses hyperinsulinemia (HI), both representing different aspects of insulin dysregulation.
• The study aimed to identify if hyperinsulinemic horses also show signs of insulin resistance and can therefore be detected by the modified 2-step Insulin Response Test using porcine zinc insulin.

Design of the Study

• The study involved 12 Icelandic horses, who were subjected to both the OGT and the 2-step IRT, following a crossover study design.
• Horses were categorized into two groups based on their serum insulin concentrations during the OGT. Six horses that showed high insulin levels were classified as hyperinsulinemic (HI), while the rest were classified as non-hyperinsulinemic (NON-HI).

Results and Key Findings

• The glucose response to IV injected PZI was measured by analysing the decline in plasma glucose concentration within the first 30 minutes.
• Both HI and NON-HI horses showed a similar reduction in glucose level over time during the 2-step IRT. Moreover, none of the horses displayed a glucose reduction of 50% or more within the 30-minute window.
• All twelve horses, including those identified as HI by the OGT, were identified as insulin-resistant by the modified 2-step IRT performed with PZI.

Implications and Conclusions

• The study suggests that both HI and NON-HI horses may show insulin-mediated glucose uptake during the modified 2-step IRT.
• This highlights the potential difficulty in choosing the correct diagnostic tool in clinical settings to assess insulin dysregulation, emphasizing the need for careful selection and interpretation of testing methods.