[The regulation of glucose production and utilization in the intact animal]

Insulin control of glucose metabolism in man: a new kinetic analysis

Analyses of the control of glucose metabolism by insulin have been hampered by changes in bloog glucose concentration induced by insulin administration with resultant activation of hypoglycemic counterregulatory mechanisms. To eliminate such mechanisms, we have employed the glucose clamp technique which allows maintenance of fasting blood glucose concentration during and after the administration of insulin. Analyses of six studies performed in young healthy men in the postabsorptive state utilizing the concurrent administration of [14C]glucose and 1 mU/kg per min (40 mU/m2 per min) porcine insulin led to the development of kinetic models for insulin and for glucose. These models account quantitatively for the control of insulin on glucose utilization and on endogenous glucose production during nonsteady states. The glucose model, a parallel three-compartment model, has a central compartment (mass = 68 +/- 7 mg/kg; space of distribution = blood water volume) in rapid equilibrium with a smaller compartment (50 +/- 17 mg/kg) and in slow equilibrium with a larger compartment (96 +/-21 mg/kg). The total plasma equivalent space for the glucose system averaged 15.8 liters or 20.3% body weight. Two modes of glucose loss are introduced in the model. One is a zero-order loss (insulin and glucose independent) from blood to the central nervous system; its magnitude was estimated from published data. The other is an insulin-dependent loss, occurring from the rapidly equilibrating compartment and, in the basal period, is smaller than the insulin-independent loss. Endogenous glucose production averaged 1.74 mg/kg per min in the basal state and enters the central compartment directly. During the glucose clamp experiments plasma insulin levels reached a plateau of 95 +/-8 microU/ml. Over the entire range of insulin levels studied, glucose losses were best correlated with levels of insulin in a slowly equilibrating insulin compartment of a three-compartment insulin model. A proportional control by this compartment on glucose utilization was adequate to satisfy the observed data. Insulin also rapidly decreased the endogenous glucose production to 33% of its basal level (0.58 mg/kg per min), this suppression being maintained for at least 40 min after exogenous insulin infusion was terminated and after plasma insulin concentrations had returned to basal levels. The change in glucose utilization per unit change in insulin in the slowly equilibrating insulin compartment is proposed as a new measure for insulin sensitivity. This defines insulin effects more precisely than previously used measures, such as plasma glucose/plasma insulin concentration ratios. Glucose clamp studies and the modeling of the coupled kinetics of glucose and insulin offers a new and potentially valuable tool to the study of altered states of carbohydrate metabolism.

Comparison of acute and subacute effects of deflazacort and prednisone on glucose metabolism in man

Corticosteroid treatment produces glucose intolerance with insulin resistance. Recent reports have indicated that deflazacort (DF) is significantly less diabetogenic than prednisone (PN). A euglycaemic hyperinsulinaemic (100 microU/ml) glucose clamp ( EHGC ) and 3H-glucose infusion for 240 min were performed in 6 healthy volunteers (HV) after administration of 15 mg PN or 18 mg DF, 12 h and 2 h before test. The glucose metabolic clearance rate (MCR) was significantly (p = 0.02) higher after DF (4.75 +/- 0.58 ml/min X kg) than after PN (3.31 +/- 0.27 ml/min X kg). Basal hepatic glucose production (HGP) was significantly (p = 0.003) lower after DF (3.58 +/- 0.33 mg/kg X min) than after PN (4.44 +/- 0.23 mg/kg X min). A similar pattern was obtained for glucose volume (GV) and glucose pool (GP). The kinetic parameters of insulin were not significantly different after the two drugs. After 7 day of PN 30 mg/day or DF 36 mg/day, EHGC and 3H-glucose infusion for 240 min were performed in 10 HV. Glucose MCR values were significantly (p = 0.03) higher after DF (5.03 +/- 0.91 ml/min X kg) than after PN (2.80 +/- 0.26 ml/min X kg). HGP values did not different significantly after the two drugs. GV (p = 0.001) and GP (p = 0.002) were significantly lower after DF than after PN. Insulin kinetics were not significantly different after the two drugs. It is concluded that on acute and 7-day administration to healthy subjects DF, in an anti-inflammatory dose equivalent to PN, shows significantly less influence on glucose metabolism.

Mechanism of action of insulin and insulin analogues. A comparison of the hepatic and peripheral effects on glucose turnover of insulin, proinsulin and three insulin analogues modified at positions A1 and B29

A [14C]-glucose tracer infusion method was used to compare the effects of insulin infusion on glucose metabolism with the effects of infusion of three semisynthetic modified insulins and of proinsulin. Insulin produced hypoglycaemia in the anaesthetised dog by decreasing hepatic glucose production and increasing peripheral glucose utilisation. Compensatory antihypoglycaemic mechanisms eventually modified these responses. A1, B29-Diacetyl insulin exerted an hypoglycaemic effect entirely by stimulation of peripheral glucose uptake. A1-B29 crosslinked insulins and proinsulin produced hypoglycaemia almost entirely by decreasing hepatic glucose production and had little effect on tissue uptake. These observations suggest that insulin analogues may have actions in vivo that are qualitatively different from those of native insulin and suggest that certain analogues have a predominant action on the liver. This has important therapeutic implications concerning the development of semisynthetic insulins for clinical use.

Some peculiarities of the glucoregulatory response to glucose infusion in the rat

The glucoregulatory response to the i.v. infusion of different doses of glucose and glucose plus insulin was studied in anesthetized rats by using the primed constant infusion of glucose-2-3H. Infusion of glucose at the rate of 10 mg/kg/min induced a rise of about 100% in blood glucose, while the hepatic release of glucose showed only a small and transient decrease. A proportional increase of glycemia and glucose utilization (Rd) was observed without any appreciable change in the metabolic clearance rate (MCR) of glucose; a two-fold increase in plasma insulin was recorded at all times. In the group of rats receiving 20 mg/kg/min of glucose, changes in the above parameters were slightly greater; MCR showed a moderate increment in spite of the six-fold rise of plasma insulin. Finally, the influsion of large doses of insulin together with 20 mg/kg/min of glucose resulted in complete cessation of glucose release by the liver and in a remarkable increase of Rd and MCR. These results suggest a poor adaptability of the glucoregulatory system of the rat in response to glucose infusion as compared to other mammalian species.