Insulin resistance in cows during the periparturient period (review)

Abstract

Insulin resistance is a state in which the biological effect of insulin is reduced when its concentration decreases or when a compensatory mechanism increases its concentration. Insulin resistance is characterized by reduced insulin response to glucose, i.e. decreased pancreatic beta cell function (insulin hyporesponsiveness) and/or reduced sensitivity of glucose to insulin (reduced intake of glucose by peripheral tissues under the influence of insulin - eng. insulin sensitivity). Methods for estimating insulin resistance include direct methods (hyperinsulinaemic-euglycaemic clamp, golden standard), indirect methods (intravenous glucose tolerance test) and surrogate methods (indices calculated from basal concentrations of insulin, glucose, NEFA and BHB-HOMA, QUICKI, RQUICKI and RQUICKI- BHB). Surrogate indices show correlations with direct and indirect test results but they are inconsistent. Inconsistency occurs because the dependence of glucose concentrations on the degree of hepatic gluconeogenesis should be kept in mind when evaluating insulin resistance in ruminants. Therefore, the hyperinsulinaemic-euglicaemic clamp method is particularly suitable as it excludes gluconeogenesis in hepatocytes from analysis. Our results have shown a correlation between HOMA, QUICKI and RQUICKI indices and metabolic profile parameters. The correlation between dynamic and basal responses of NEFA, BHB, insulin, glucose and inorganic phosphorus is significantly dependent on RQUICKI-BHB index values in ketotic cows. RQUICKI index of insulin resistance is substantially dependent on NEFA values in early lactation as well as on insulin and glucose values in the dry period. Further investigations should focus on the practical evaluation of the use of insulin resistance indices.