Showing papers by "Richard N. Bergman published in 1988"
TL;DR: The results suggest that the one-compartment, fixed-pool volume model of glucose kinetics is insufficient to account for the complex dynamics of labeled and unlabeled glucose during euglycemic-hyperinsulinemic clamps.
Abstract: We previously demonstrated that conventional tracer methods applied to euglycemic-hyperinsulinemic glucose clamps result in substantially negative estimates for the rate of endogenous glucose production, particularly during the first half of 180-min clamps. We also showed that addition of tracer to the exogenous glucose infusate resulted in nonnegative endogenous glucose production (Ra) estimates. In this study, we investigated the underlying cause of negative estimates of Ra from conventional clamp/tracer methods and the reason for the difference in estimates when tracer is added to the exogenous glucose infusate. We performed euglycemic-hyperinsulinemic (300-microU/ml) clamps in normal dogs without (cold GINF protocol, n = 6) or with (hot GINF protocol, n = 6) tracer (D-[3-3H]glucose) added to the exogenous glucose infusate. In the hot GINF protocol, sufficient tracer was added to the exogenous glucose infusate such that arterial plasma specific activity (SAa) did not change from basal through the clamp period (P greater than .05). In the cold GINF studies, plasma SAa fell 81 +/- 2% from the basal level by the 3rd h of clamping. We observed a significant, transient, positive venous-arterial difference in specific activity (SAv-SAa difference) during the cold GINF studies. The SAv-SAa difference reached a peak of 27 +/- 6% at 30 min and diminished to a plateau of 7 +/- 1% between 70 and 180 min. We also observed a positive but constant SAv-SAa difference (4.6 +/- 0.2% between 10 and 180 min) during the hot GINF studies. The observations of a difference between hot and cold GINF endogenous Ra estimates and a positive but transient SAv-SAa difference during the cold GINF studies are consistent with the interpretation that a portion of the underestimation of Ra is due to insufficient mixing of endogenous and exogenous glucose for the one-compartment, fixed-pool volume model to be applicable. Alternatively, our results suggest that the one-compartment, fixed-pool volume model of glucose kinetics is insufficient to account for the complex dynamics of labeled and unlabeled glucose during euglycemic-hyperinsulinemic clamps. Improved mixing through addition of tracer to the exogenous glucose infusate or improved modeling by allowing for a variable-pool volume appears to improve the accuracy of the tracer methods; however, these approaches remain to be validated. The constant positive SAv-SAa difference observed during the hot GINF studies is consistent with the interpretation that an additional contributor to underestimation of endogenous Ra is apparent isotope discrimination.(ABSTRACT TRUNCATED AT 400 WORDS)
179 citations
TL;DR: During the preclinical period of human insulindependent diabetes, both impaired pancreatic β-cell function and increased insulin resistance are found, although normoglycemia is preserved, and in adolescent male baboons both in normal health and after a small dose of streptozocin which did not induce hyperglycemia.
Abstract: During the preclinical period of human insulin-dependent diabetes, both impaired pancreatic beta-cell function and increased insulin resistance are found, although normoglycemia is preserved. To better understand the changes in beta-cell function and insulin sensitivity that occur in preclinical insulin-dependent diabetes, we performed a panel of in vivo beta-cell function tests and measured insulin sensitivity in adolescent male baboons both in normal health and after a small dose of streptozocin which did not induce hyperglycemia. Nine animals were studied before (stage 1) and 1 week after receiving a low dose of streptozocin (stage 2). There was no change in fasting plasma glucose or insulin. The mean glucose disposal rate (Kg) remained within the normal range, but dropped from 2.0 +/- 0.2% +/- SE) to 1.2 +/- 0.1%/min (P less than 0.01), the acute insulin response to arginine (AIR(arg)) fell from 67.7 +/- 19.4 microU/mL (485.8 +/- 139.2 pmol/L) to 32.8 +/- 7.2 microU/mL (235.3 +/- 51.7 pmol/L; P less than 0.05), and the acute insulin response to glucose (AIR(gluc)) fell from 881 +/- 243 microU/mL.10 min (6321 +/- 1744 pmol/L.10 min) to 334 +/- 82 microU/mL.10 min (2396 +/- 588 pmol/L.10 min; P less than 0.01). The most dramatic change, however, was in the ability of hyperglycemia to potentiate AIR(arg) (expressed as the slope of potentiation). This was reduced by 94% from 1.8 +/- 0.5 to 0.1 +/- 0.1 (P less than 0.01), with almost no overlap in values between stages 1 and 2. Insulin sensitivity was also lower 1 week after streptozocin treatment. When the animals were restudied 8 weeks after streptozocin treatment (stage 3) most measures of beta-cell function were not significantly different from those in stage 1. The fasting plasma glucose level was 85.4 +/- 4.3 mg/dL (4.7 +/- 0.2 mmol/L), Kg was 1.8 +/- 0.3%/min, fasting plasma insulin was 35.9 +/- 8.5 microU/mL (257.6 +/- 61.0 pmol/L), AIR(arg) was 67.0 +/- 15.4 microU/mL (480.7 +/- 110.5 pmol/L), and AIR(gluc) was 615.3 +/- 265.3 microU/mL.10 min (4413 +/- 1901 pmol/L.10 min), and tissue insulin sensitivity was 2.7 +/- 0.4 x 10(4) min/microU.mL. These values show extensive overlap with those of stage 1, from which they are not significantly different. The slope of glucose potentiation, however, remained low in all animals at stage 3.(ABSTRACT TRUNCATED AT 400 WORDS)
43 citations
TL;DR: The results indicate that glucoreceptor cells in tissues perfused by carotid arteries may play a tautological role in the sympathetic response to hypoglycemia and imply that glucose-sensitive receptors must also be located elsewhere in the central nervous system or in the periphery.
Abstract: In the present study we examined whether the magnified hormonal counter-regulatory response seen during deep hypoglycemia (40 mg/dl) could be attenuated by supplying the forebrain with glucose furnished through carotid infusion. Two protocols were performed in conscious dogs. In the first protocol we infused glucose bilaterally into the carotid circulation to produce a forebrain glycemia of 55 +/- 1 mg/dl (as reflected in the jugular vein), whereas systemic glycemia declined to 39 +/- 2 mg/dl. In the second protocol as a control we infused glucose into the systemic circulation at a rate matched to protocol 1 so that both systemic and jugular plasma glucose concentrations were equivalent to the systemic glucose concentrations in protocol 1 (jugular, 41 +/- 3 mg/dl; systemic, 40 +/- 2 mg/dl; P greater than 0.9). In spite of a substantial difference in forebrain glycemia (55 mg/dl compared with 41 mg/dl) there were no differences in the counter-regulatory responses of catecholamines or glucagon. In addition, through the use of radiolabeled microspheres, we defined the precise regions of the forebrain irrigated during bilateral intracarotid glucose infusions. The concentration of microspheres was high in the forebrain but very low in the hindbrain. Our results indicate that glucoreceptor cells in tissues perfused by carotid arteries may play a tautological role in the sympathetic response to hypoglycemia and imply that glucose-sensitive receptors must also be located elsewhere in the central nervous system or in the periphery.
15 citations
TL;DR: The optimal segments technique is a new approach to smoothing and interpolating between small numbers of discrete biological data that is useful for the analysis of biological signals such as plasma measurements of hormone and metabolite concentration.
10 citations
Journal Article•
TL;DR: It is argued that the maximum usefulness of models can be obtained with respect to the testing of specific physiological hypotheses, and the estimation of unmeasurable parameters or variables from an optimization procedure.
Abstract: Fundamentals of modeling of in vivo nutritional and metabolic systems are discussed Emphasis is placed upon the potential usefulness of models, and the relationship between utility and model complexity With the glucose regulating system used as a metaphoric example, the balance between available data and model simplification is drawn, with the goal of obtaining a representation of optimal complexity From such an optimization procedure, it is argued that the maximum usefulness of models can be obtained with respect to the testing of specific physiological hypotheses, and the estimation of unmeasurable parameters or variables The view is expressed that only with careful modeling procedures, in which principles of optimal complexity are applied, will the impact of models of nutritional systems be significant
3 citations