Estimation of Hepatic Glucose Output in Non-Steady State. The Simultaneous Use of 2-3H-glucose and 14C-glucose in the Dog

Abstract

The rate of appearance of glucose (Ra) was estimated in a non-steady state caused by the infusion of glucose (exogenous increase of Ra) or glucagon (increase of hepatic glucose output) in unanesthetized dogs with indwelling arterial and venous catheters. First, Ra was measured with 2-3H-glucose according to the primed constant rate infusion technique in steady state, then with the onset of the perturbation the infusion of a second tracer, (U) 14C-glucose, was started. Exponential functions were fitted to the two specific activity curves. The second tracer made it possible to calculate Ra during the non-steady state without the need to assume a definite value for the "miscible" glucose space (V). The latter could also be calculated and it proved to be a single exponential function of time elapsed from the start of the perturbation. In the first few minutes the glucose load (10 or 15 mg/kg min for 120 min) caused a sharp fall of hepatic glucose output. This was followed by a rise of various degrees before the endogenous glucose output reached the steady state at about 50 or 70% below the base-line values. During the glucose load, in steady state (U) 14C-glucose as a tracer gave about 10% lower values for Ra than tritiated glucose.