Type 2 diabetic patients have increased gluconeogenic efficiency to substrate availability, but intact autoregulation of endogenous glucose production.
OBJECTIVE
An autoregulatory mechanism involving a reciprocal relationship between gluconeogenesis and glycogenolysis regulates endogenous glucose production (EGP) in healthy individuals. In type 2 diabetes, fasting hyperglycemia may be due to increased EGP.


METHODS
To examine gluconeogenesis and autoregulation of EGP in type 2 diabetes, 9 type 2 diabetics and 8 healthy controls were studied during a 3-h infusion of 30 micromol/kg/min Na-lactate. The diabetics were also studied during a control infusion of Na-bicarbonate. To standardize levels of glucoregulatory hormones, plasma insulin, growth hormone, and glucagon were clamped at identical levels during the three experiments. Glucagon levels were elevated from basal levels to approximately 330 ng/l when the lactate or bicarbonate infusions were started, in order to mimic the hyperglucagonemia often seen in diabetes. Lactate gluconeogenesis and total EGP were measured by infusions of [6-(3)H] glucose and [U-14C] lactate.


RESULTS
In the bicarbonate experiments, hyperglugagonemia increased lactate gluconeogenesis in the diabetic patients from 4.3+/-1.8 to 6.1+/-2.4 micromol/kg/min (p=0.04). EGP did not change significantly (basal EGP: 15.3+/-3.9, EGP at the end of the study: 14.2+/-3.9 micromol/kg/min, p=0.14). During both lactate experiments, plasma lactate increased more than 4-fold. The increase in lactate gluconeogenesis was significantly higher in diabetics than in controls (values obtained at the end of experiments minus basal values: 10.8+/-3.6 versus 6.4+/-3.6 micromol/kg/min, p=0.03). Compared with normal subjects, the diabetic patients had higher EGP values both at basal conditions (p=0.001) and during lactate infusion (p=0.005). Despite augmented gluconeogenesis, EGP did not change during lactate and glucagon infusion in any of the groups (diabetics, basal EGP: 15.4+/-2.7 versus EGP at the end of experiments: 15.6+/-3.6 micromol/kg/min, p>0.30. Controls, basal EGP: 11.8+/-0.8 versus EGP at the end of experiments: 11.6+/-1.9 micromol/kg/min, p>0.30).


CONCLUSIONS
Although type 2 diabetics have increased EGP and increased lactate gluconeogenesis, the hepatic autoregulation of EGP during increased substrate-induced gluconeogenesis seems to be intact.
Toft
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Department of Nephrology, University Hospital of Northern Norway, Tromsø. ingrid.toft@unn.no
Jenssen
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D000328:Adult; D002096:C-Peptide / Q000097:blood; D003924:Diabetes Mellitus, Type 2 / Q000378:metabolism*; D005230:Fatty Acids, Nonesterified / Q000097:blood; D005260:Female; D005934:Glucagon / Q000097:blood; D005943:Gluconeogenesis / Q000502:physiology*; D005947:Glucose / Q000096:biosynthesis* / Q000493:pharmacokinetics; D015309:Glucose Clamp Technique; D006706:Homeostasis / Q000502:physiology*; D019382:Human Growth Hormone / Q000097:blood; D006801:Humans; D007328:Insulin / Q000097:blood; D008099:Liver / Q000378:metabolism; D008297:Male; D008875:Middle Aged; D017693:Sodium Bicarbonate / Q000493:pharmacokinetics; D019354:Sodium Lactate / Q000493:pharmacokinetics*
D002096:C-Peptide; D005230:Fatty Acids, Nonesterified; D007328:Insulin; D019382:Human Growth Hormone; D017693:Sodium Bicarbonate; D005934:Glucagon; D005947:Glucose; D019354:Sodium Lactate