Hepatic glycogen is replenished during the absorptive period postprandially. This repletion is prompted partly by an increased hepatic uptake of glucose by the liver, partly by metabolite and hormonal signals in the portal vein, and partly by an increased gluconeogenic flux to glycogen (glyconeogenesis). There is some evidence that the direct formation of glycogen from glucose and that formed by gluconeogenic pathways is linked. This includes: (i) the inhibition of all glycogen synthesis, in vivo, when gluconeogenic flux is blocked by inhibitors; (ii) a dual relationship between glucose concentrations, lactate uptake by the liver and glycogen synthesis (by both pathways) which indicates that glucose sets the maximal rates of glycogen synthesis while lactate uptake determines the actual flux rate to glycogen; (iii) the decrease of both gluconeogenesis and glycogen synthesis by the biguanide, metformin; and (iv) correlations between increased gluconeogenesis and liver glycogen in obese patients and animal models. The degree to which the liver extracts portal glucose is not entirely agreed upon although a preponderance of evidence points to about a 5% extraction rate, following meals, which is dependent on a stimulation of glucokinase. This enzyme may be linked to the expression of other enzymes in the gluconeogenic pathway. Perivenous cells in the liver may induce additional gluconeogenesis in the periportal cells by increasing glycolytically produced lactate. A number of potential mechanisms therefore exist which could link glycogen synthesis from glucose and gluconeogenic substrate.

Aims/hypothesis: An increase in endogenous glucose production (EGP) is a major contributor to fasting morning hyperglycaemia in type 2 diabetes. This increase is dissipated with fasting, later in the day. To understand its origin, EGP, gluconeogenesis and hormones that regulate metabolism were measured over 24 h. We hypothesised that EGP, and therefore glycaemia, would demonstrate a centrally mediated circadian rhythm in type 2 diabetes. Subjects and methods: Seven subjects with type 2 diabetes and six age-and BMI-matched control subjects, fasting after breakfast (08

To directly assess the effects of the biguanide, metformin, on hepatic gluconeogenesis, it was added at high therapeutic levels (90 microg/ml) to the medium perfusing an isolated rat liver. Lactate (1 mg/min) was infused simultaneously along with [14C]lactate with or without [3H]lactate. [6-(3)H]glucose was added at the beginning of the perfusion in studies where [3H]lactate was not infused. Glucose levels decreased relative to control studies (metformin dose = 0) and lactate concentrations increased in this closed system. Quantitative analysis of the relationship between labeled glucose and lactate indicated that the flux of carbon from lactate to glucose and CO2 was halved, whereas reflux from glucose to lactate increased by approximately 80%. This was corroborated by measurement of labeled lactate extraction as well as glucose, CO2, and lactate production across the liver. Glycogen content of the liver fell by 60% relative to control and was greater for the gluconeogenic pathway. These data are consistent with an inhibitory action of metformin on gluconeogenesis, which is due to a primary inhibition of hepatic lactate uptake.

The relative importance of glucose over-production and inadequate peripheral removal in the postabsorptive (fasting) hyperglycaemia of Type II (non-insulin dependent) diabetes mellitus has produced diverse estimates. Some studies show that a strong correlation exists between fasting glucose concentrations and its production over a wide range of glycaemia, suggesting a causative role for excessive glucose output in hyperglycaemia [1,8]. Other measurements, however, show almost no correlation between glucose production rates and concentrations [9±14], Diabetologia (2001) AbstractAims/hypothesis. The pathogenesis of fasting hyperglycaemia in Type II (non-insulin-dependent) diabetes mellitus has yet to be clarified. Rates of glucose production (R a ), utilization and metabolic clearance rate were therefore measured during an extended fast, in control subjects and in Type II diabetic patients. Methods. Nine subjects with newly-diagnosed or diettreated diabetes and seven control subjects matched for age and weight (BMI 36.0 2.4 and 35.3 3.1 kg/ m 2 respectively) underwent an overnight fast followed by a 10-h unprimed infusion of [6-3 H]glucose. Plasma tracer concentrations were fitted by a singlecompartment model. Results. The metabolic clearance rate was near-constant [61.7 + 2.4 ml/(min-m 2 )] in diabetic patients and [75.5 3.3 ml/(min-m 2 )] in control subjects (p < 0.05). It was correlated to the glucose concentrations both at t = 0 (r = ±0.752, p = 0.0008) and t = 10 h (r = ±0.675, p = 0.004). The calculated volume of distribution was 17.3 1.4 l (18.2 % weight, diabetes), 19.6 2.4 l (18.4 % weight, control). Glycaemia fell from 10.7 0.8 mmol/l to 6.5 0.3 mmol/l by 10 h (p < 0.05) in diabetes and from 5.6 0.6 to 4.8 0.1 mmol/l in control subjects (p < 0.05). The rate of glucose production decreased in parallel, from 563 33 to 363 23 mmol/(min-m 2 ) (p < 0.05) in diabetes from 419 20 to 347 32 mmol/(min-m 2 ) in control subjects. Initial R a was higher in diabetic patients than in control subjects (p < 0.05) and was highly correlated to glycaemia (r = 0.836, p = 0.0001). By 10 h, R a had converged in diabetic patients and control subjects and all correlation with glycaemia was lost (r = 0.0017, p = 0.95). Conclusions/interpretation. In relatively early diabetes, the more ªlabileº portion of fasting hyperglycaemia, which subsequently decreased, was closely related to the simultaneously decreasing R a . The 25 % increase in glucose concentrations which persisted as stabilized R a , resulted from about a 20 % lower metabolic clearance rate. [Diabetologia (2001) 44: 983± 991]

Soluble preparations of [LysB28,ProB29]-human insulin analogue (LysPro) exhibit more rapid absorption than human insulin upon subcutaneous injection. Biphasic mixtures of LysPro and intermediate-acting insulin suspensions could provide advantages over current preparations for the treatment of diabetes. To prepare biphasic mixtures of LysPro, a suspension formulation of the analogue is required. We have devised a method for crystallizing LysPro with the basic peptide protamine yielding neutral protamine LysPro (NPL) suspension. The crystallization conditions are strongly dependent on the precipitation procedure and temperature. Using various techniques, the crystalline and suspension characteristics of NPL are found to be similar to human insulin (neutral protamine Hagedorn, NPH) (8:1 molar ratio insulin:protamine, rod-shaped crystals, particle size of 4.0-6.0 microns, and Point of Zero Charge at 6.0-7.0). Using a dog model with NPL or NPH injected subcutaneously and glucose levels clamped at basal, NPL was found to have kinetic and dynamic responses analogous to human insulin NPH [Cmax (maximal insulin or LysPro concentration, ng/mL) of 2.61 +/- 0.22, NPL; 2.58 +/- 0.36, NPH, attained at Tmax (min) of 93 +/- 22, NPL; 145 +/- 33 NPH, and Rmax (maximal rate of glucose infusion, mg/kg min) of 10.8 +/- 1.2, NPL; 13.2 +/- 1.9, NPH, attained at TRmax (min) of 277 +/- 58, NPL; 265 +/- 38, NPH]. There are no statistically significant differences between the insulin curves or the glucose responses. These results provide insight into the mechanism of action of NPH suspensions and the relationship to duration of action. Furthermore, the formulation of a suspension of LysPro having an intermediate time-action makes possible the preparation of stable biphasic mixtures containing LysPro and NPL.

The absorption of a bolus of intraperitoneal insulin into the splanchnic and peripheral circulations was separately assessed in dogs using an infusion of two insulin tracers (A1-[3H]insulin and B1-[3H]insulin). One tracer was infused into the superior mesenteric artery and the second into the jugular vein. Serial samples were taken before and after an injection of insulin (1 U/kg ip). Sampling was from the portal vein and the inferior vena cava. By using the principle of equivalent entry of tracer and unlabeled material, we developed two simultaneous equations for the rate of splanchnic and peripheral insulin absorption at each time point. These were solved to yield the two rates. Mean concentrations in the portal vein were approximately 25% higher than in the inferior vena cava, reflecting the splanchnic absorption. This rate accounted for almost half (51 +/- 9%) of the insulin absorbed. The remainder of the absorption was peripheral. The total recovery of intraperitoneal insulin, absorbed by either route, was 88 +/- 11%. Portal absorption peaked earlier than peripheral. Absorption by both routes was 90% complete within approximately 2 h (131 +/- 16 min). In summary, therefore, intraperitoneal insulin is rapidly and almost completely absorbed, with absorption split between the splanchnic and peripheral routes of entry.

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