Rates of Removal of Exogenous and Endogenous Glucagon From the Plasma of Sheep in Vivo

Abstract

The removal of exogenous and endogenous glucagon from plasma was determined in vivo in sheep weighing 53�1 (mean�s.e.) kg. Porcine glucagon was infused intravenously for 90 min. The metabolic clearance rates (MCR) were determined from plateau immunoreactive glucagon (IRG) concentrations in plasma and infusion rates of glucagon. The mean clearance rate (�s.e.) was 16�7�1�6 litres per hour (n = 20). Upon termination of the infusion, the decrease in IRG concentrations in plasma was determined. Least-squares regression analysis of non-linear functions indicated the data fit a two-component exponential function. The time constant for the rapid component of the plasma IRG disappearance function was -0�32�0�04 min- 1 (mean�s.e.). The time constant for the slow component was -0�022�0�008 min-'. The rate of removal of endogenous glucagon was estimated during the infusion of somatostatin when glucagon secretion was inhibited. The time constants (mean�s.e., n = 8) for the decrease in IRG during somatostatin infusion were -0�42�0�08 and -0�003�0�002 min-' for fast and slow components, respectively. The time constants for the rapid components of exogenous and endogenous glucagon were not significantly different. This suggests that endogenous and exogenous glucagon are similarly removed from plasma.