Kinetic studies on hepatic handling of glucagon using the model of non-recirculating perfused rat livers

Using the model of the in vitro non-recirculating perfused rat liver we studied kinetic aspects of the hepatic handling of glucagon. Under conditions of a 20 min glucagon infusion (glucagon mass flows of 0.05, 0.46 and 4.75 ng/g liver/min, respectively) according to a rectangular profile both total and individual glucagon extractions were dependent on mass flow and time. The time course of glucagon extraction started with an acute phase within the first minute of infusion with a maximum value of 70%, which decreased within the following 30 sec by more than 40%. Depending on concentration, there was a progressive decrease in the hepatic extraction of glucagon up to the end of perfusion. Hepatic glucagon degradation was found to take place only at a little extent. Immediately after terminating the hormone infusion, the liver changed over into a glucagon-releasing organ. Kinetics of glucagon infusion and glucagon-induced hepatic glycogenolysis did not distinguish by parallelism but rather by phase shifting.