The relationship between plasma concentration and disappearance rate of immunoreactive insulin in the conscious dog

The relationship between plasma concentration and disappearance (infusion) rate of insulin was determined during infusion of insulin via the portal circulation of 14 normal euglycaemic dogs when somatostatin was infused to block endogenous insulin secretion. The relationship could be represented by one straight line over the plasma immunoreactive insulin range 0 to 110 microU/ml (r = 0.99) but above 110 microU/ml the fractional insulin disappearance rate declined. The results indicate the existence in the dog of a saturable pathway of insulin degradation that could conceivably be located in liver and which may become saturated only at insulin concentrations in the portal vein exceeding approximately 330 microU/ml.