Penny Wallace

Metabolic Effects of New Oral Hypoglycemic Agent CS-045 in NIDDM Subjects

Objective — To study the metabolic effects of a new oral antidiabetic agent, CS-045, in subjects with non-insulin-dependent diabetes mellitus (NIDDM). Research Design And Methods — Eleven NIDDM subjects (mean age 59 yr and body mass index 32.3) were treated with 400 mg/day CS-045 for 6-12 wk. Patients were hospitalized before and at the end of the drug-treatment period for metabolic studies, including oral glucose tolerance test (OGTT), meal tolerance test (MTT), euglycemic glucose-clamp studies, and lipid analyses. Results — Eight subjects showed a marked clinical response to the drug, whereas 3 were nonresponders. The data were analyzed both for the total group and for the responders. Fasting plasma glucose (FPG) fell from 12.5 ± 0.7 to 10.7 ± 1.0 mM in the total group but fell more dramatically from 12.7 ± 0.5 to 8.3 ± 0.6 mM in the responder group. The area under the OGTT glucose curve improved by 17% in the total group and by 29% in the responders. The area under the MTT glucose curve improved by 38 and 52%, respectively. MTT levels of insulin, free fatty acids, and glucagon were significantly lower after treatment. Glucose disposal rates during glucose-clamp studies were increased in all subjects after CS-045 treatment. Mean increases were 63% at 120 mU · m−2 · min−1 and 41% at 300 mU · m−2 · min−1. Basal hepatic glucose production fell by 17% in the total group and by 28% in the responders. Conclusions — CS-045 improves insulin resistance, reduces insulinemia, lowers hepatic glucose production, and improves both fasting and postprandial glycemia in NIDDM subjects. CS-045 may represent a new therapeutic option for NIDDM.

Intensive Conventional Insulin Therapy for Type II Diabetes: Metabolic effects during a 6-mo outpatient trial

Objective— To determine whether tight glycemic control can be obtained using intensive conventional split-dose insulin therapy in the outpatient management of type II diabetes without development of unacceptable side effects. Research Design and Methods— Fourteen type II diabetic subjects were treated with an intensive program of conventional insulin (subcutaneous NPH and regular insulin before breakfast and supper) for 6 mo. Insulin dose adjustments were based on an algorithm built on frequent CPG measurements (4–6 times/day). Patients were monitored biweekly as outpatients and admitted 1 day/mo for metabolic evaluation. Results— Glycemic control was achieved by 1 mo (mean plasma glucose fell from 17.5 ± 0.9 to 7.7 ± 0.7 mM, P < 0.001) and remained in this range thereafter. Hypoglycemic events at 1 mo were infrequent (mean ± SE events per patient per month: 4.1 ± 0.3) and mild in nature, and progressively decreased to 1.3 ± 0.5 events/mo by 6 mo. After treatment, basal HGO fell 44% from 628 ± 44 to 350 ± 17 μmol·m−2·min−1 (P < 0.001), and maximal rates of glucose disposal measured by hyperinsulinemic euglycemic clamp (1800 pmol·m−2·min−1) improved from 1418 ± 156 to 1657 ± 128 μmol·m−2·min−1 (P < 0.05). The total dose of exogenous insulin required was 86 ± 13 U at 1 mo and 100 ± 24 U at 6 mo. During treatment, mean serum insulin levels increased from 308 ± 80 to 510 ± 102 pM (P < 0.05), while body weight increased from 93.5 ± 5.8 to 102.2 ± 6.8 kg (P < 0.001). Both pre- and posttreatment glucose disposal rates correlated with the total exogenous insulin dose required to achieve glycemic control (r = −0.75 and −0.78, both P < 0.005). Weight gain was inversely related to the pretreatment glucose disposal rate (r = −0.53, P < 0.05) and directly correlated with both mean day-long serum insulin level (r = 0.67, P < 0.01) and total exogenous insulin dose (r = 0.62, P < 0.02). Conclusions— Intensive CIT, when combined with CBG measurements, can be used to rapidly improve glycemic control in type II diabetes without development of unacceptable hypoglycemia. This degree of metabolic improvement, however, requires large doses of exogenous insulin to overcome peripheral insulin resistance and results in greater hyperinsulinemia with progressive weight gain.

Kinetics of In Vivo Muscle Insulin-Mediated Glucose Uptake in Human Obesity

The kinetics of in vivo insulin-mediated glucose uptake in human obesity have not been previously studied. To examine this, we used the glucose-clamp technique to measure whole-body and leg muscle glucose uptake in seven lean and six obese men during hyperinsulinemia (∼2000 pM) at four glucose levels (∼4.5, ∼8.3, ∼13.5, and ∼23.5 mM). To measure leg glucose uptake, the femoral artery and vein were catheterized, and blood flow was measured by thermodilution (leg glucose uptake = arteriovenous glucose difference × blood flow). With this approach, we found that rates of whole-body and leg glucose uptake were significantly lower in obese than in lean subjects at each glucose plateau. Leg blood flow rates increased from 4.3 ± 0.4 to 6.5 ± 0.8 dl/min over the range of glucose in lean subjects (P < 0.05) but remained unchanged in obese subjects. The apparent maximal capacity (Vmax), based on whole-body and leg glucose uptake, was reduced in obese compared with lean subjects, but the apparent Km was similar in the lean and obese subjects (6-9 mM, NS). To assess the affinity of muscle for glucose extraction independent of changes in muscle plasma flow, we determined the mean half-maximal effective glucose concentration (EG50) and found it was similar in the lean and obese subjects (6.0 ± 0.3 vs. 6.0 ± 0.8 mM, NS). We conclude that 1) the kinetics of in vivo insulin-mediated glucose uptake in skeletal muscle in human obesity are characterized by reduced Vmax but normal Km; 2) the EG50 for insulin-mediated glucose extraction in skeletal muscle was 6 mM in both lean and obese subjects, consistent with a Km characteristic of the glucose-transport system; 3) obese subjects were unable to generate increases in blood flow in response to hyperglycemia under hyperinsulinemic conditions, and this contributed significantly to lower rates of leg and whole-body glucose uptake.

Direct and Indirect Effects of Insulin to Inhibit Hepatic Glucose Output in Obese Subjects

The effects of small increases in plasma insulin on hepatic glucose production are incompletely understood. To partially elucidate this issue we have studied seven obese subjects with the euglycemic clamp technique with a low-dose insulin infusion rate of 15 mU · m−2 · min−1 over 3 h. Basal insulin levels were 24 ± 7 μU/ml and increased to steady-state levels of 35 ± 3 μU/ml during insulin infusion. Endogenous insulin secretion, quantitated by C-peptide measurements, decreased by 58% of the basal value after peripheral insulin infusion. Based on C-peptide measurements and the contribution of the peripheral insulin infusion to the circulating insulin concentrations, calculated portal insulin levels either decreased or remained unchanged during the clamp studies. Basal glucagon levels were 165 ± 18 and did not change during the insulin infusion. The basal glucose disposal rate was 86 ± 2 mg · m−2 · min−1 and did not increase significantly during the clamp studies. In contrast, hepatic glucose output (HGO) was suppressed by 82 ± 5% of the basal value. In summary, in a group of insulin-resistant obese subjects, glucose-clamp studies were performed at peripheral insulin levels of 35 ± 3 μU/ml; glucose disposal did not increase, whereas HGO was suppressed by 82%. At the same time, glucagon levels remained constant and estimated portal insulin levels either decreased or remained unchanged. These findings suggest that insulin can suppress HGO through indirect extrahepatic actions.

Kinetics of Insulin-Mediated and Non-Insulin-Mediated Glucose Uptake in Humans

The kinetics of insulin-mediated glucose uptake (IMGU) and non-insulin-mediated glucose uptake (NIMGU) in humans have not been well defined. We used the glucose-clamp technique to measure rates of wholebody and leg muscle glucose uptake in six healthy lean men during hyperinsulinemia (∼460 pM) to study IMGU and during somatostatin-induced insulinopenia to study NIMGU at four glucose levels (4.5, 9,12, and 21 mM). To measure leg glucose uptake, the femoral artery and vein were catheterized, and blood flow was measured by thermodilution (leg glucose uptake = arteriovenous glucose difference [A-VG] × blood flow). With this approach, we found that, during hyperinsulinemia, both whole-body and leg glucose uptake increased in a curvilinear fashion at every glucose level, the highest glucose uptake values obtained being 139 ± 17 μmol · kg−1 · min−1 and 3656 ± 931 μmol · min−1 · leg−1, respectively. Leg blood flow increased twofold from 6.0 ± 1.7 to 11.7 ± 3.1 dl/min (P < 0.01) over the range of glucose and was correlated with whole-body glucose uptake (r = 0.55, P < 0.005). Leg muscle glucose extraction, independent of changes in blood flow, which is reflected by the A-VG, saturated over the range of glucose (1.28 ± 0.12, 2.22 ± 0.30, 2.92 ± 0.42, 3.02 ± 0.41 mM, NS between last 2 values) with a halfmaximal effective glucose concentration (EGS0) of 5.3 ± 0.4 mM. During insulinopenia, both whole-body and leg glucose uptake increased in a near-linear fashion; however, glucose uptake remained significantly lower than that seen with insulin stimulation, the highest glucose uptake values obtained being 22 ± 2 μmol · kg−1 · min−1 and 260 ± 34 μmol · min−1 · leg1, respectively. Leg blood flow was unchanged from the basal value (4.15 ± 0.63 dl/min) over the range of glucose studied, and A-VG increased at all glucose levels: 0.094 ± 0.010, 0.28 ± 0.03, 0.38 ± 0.04, and 0.59 ± 0.03 mM (P < 0.05 between any 2 consecutive values), with an EG50 of 10.0 ± 0.4 mM (P < 0.001 vs. IMGU). We conclude that 1) insulin increases the capacity for muscle A-VQ approximately fivefold; 2) muscle IMGU, independent of blood flow, displays an EG50 similar to the Km characteristic of the glucose-transport system (∼5–6 mM); 3) in contrast, NIMGU is a low-affinity glucoseuptake system; and 4) blood flow to insulin-sensitive tissue increases with insulin and glucose infusions and is an important determinant of the rate of in vivo glucose uptake.

In vivo regulation of non-insulin-mediated and insulin-mediated glucose uptake by cortisol

In vivo glucose uptake (Rd) occurs via two mechanisms: insulin-mediated glucose uptake (IMGU), which occurs in insulin-sensitive tissues, and noninsulin-mediated glucose uptake (NIMGU), which occurs in both insulin-sensitive and non-insulinsensitive tissues. To determine whether these two pathways for in vivo glucose disposal are regulated independently, we studied the effect of stress levels of cortisol on IMGU and NIMGU in seven normal subjects after an overnight fast. To study NIMGU, somatostatin (SRIF, 600 μg/h) was infused to suppress endogenous insulin secretion and create severe insulinopenia, and glucose turnover was measured isotopically while serum glucose was clamped at ∼200 mg/dl for 240 min. Separate studies were performed during the overnight infusion of saline or hydrocortisone (HCT; 2.0 μg · kg−1 · min1). The final 120 min of each study were used for data analysis. Under these conditions, insulin action is absent, and Rd = NIMGU. NIMGU was 204 ± 11 mg/min and 208 ± 8 mg/dl during saline and HCT, respectively (P NS). Therefore, HCT did not modulate NIMGU. To measure the effect of cortisol on Rd, hyperglycemic (200 mg/dl)-hyperinsulinemic clamp studies (30 mU · m−2 · min1) were performed during the infusion of saline or HCT. The results demonstrate that during saline infusion, steady-state rates of Rd (10.4 ± 0.8 mg · kg−1 · min1) were achieved by 160 min; in contrast, during HCT infusion, Rd never reached steady state but increased from 4.5 ± 0.2 in the 2nd h to 7.6 ± 0.4 mg kg1 min1 in the 4th h, P < .01. In conclusion, 1) cortisol has no measurable modulatory effect on NIMGU, 2) IMGU and NIMGU are independently regulated and functionally distinct, and 3) cortisol causes insulin resistance by causing a decrease in the rate at which insulin activates the glucose uptake system.

Effects of Fasting on Plasma Glucose and Prolonged Tracer Measurement of Hepatic Glucose Output in NIDDM

We studied the measurement of hepatic glucose output (HGO) with prolonged [3-3H]glucose infusion in 14 patients with non-insulin-dependent diabetes mellitus (NIDDM).Over the course of 10.5 h, plasma glucose concentration fell with fasting by one-third, from 234 ± 21 to 152 ± 12 mg/dl, and HGO fell from 2.35 ± 0.18 to 1.36 ± 0.07 mg · kg−1 · min−1 (P < .001). In the basal state, HGO and glucose were significantly correlated (r = 0.68, P = .03), and in individual patients, HGO and glucose were closely correlated as both fell with fasting (mean r = 0.79, P < .01). Plasma [3-3H]glucose radioactivity approached a steady state only 5-6 h after initiation of the primed continuous infusion, and a 20% overestimate of HGO was demonstrated by not allowing sufficient time for tracer labeling of the glucose pool. Assumption of steadystate instead of non-steady-state kinetics in using Steeles equations to calculate glucose turnover resulted in a 9-24% overestimate of HGO. Stimulation of glycogenolysis by glucagon injection demonstrated no incorporation of [3-3H]glucose in hepatic glycogen during the prolonged tracer infusion. In a separate study, plasma glucose was maintained at fasting levels (207 ± 17 mg/dl) for 8 h with the glucose-clamp technique. Total glucose turnover rates remained constant during this prolonged tracer infusion. However, HGO fell to 30% of the basal value simply by maintaining fasting hyperglycemia in the presence of basal insulin levels. Inconclusion, elevated HGO is a major determinant of fasting hyperglycemia in NIDDM, and the close relationship of plasma glucose and HGO is maintained as both fall during a day-long fast. Insufficient time for tracer equilibration, and assumption of steady-state kinetics may result in significant overestimates of HGO. HGO is suppressed by 70% when the fall in glucose level is prevented by performing a glucose clamp at the fasting glucose level. This effect should be considered in studies with the isoglycemic clamp technique to study effects of interventions on HGO of NIDDM.

Hyperinsulinemia Does Not Compensate for Peripheral Insulin Resistance in Obesity

Based on previous steady-state measures of the biologic activity of insulin, it was thought that postprandial hyperinsulinemia in obesity compensated for insulin resistance. However, we recently demonstrated kinetic defects in insulin action in insulin-resistant nondiabetic obese subjects: activation of insulin-stimulated glucose disposal was slower and deactivation was faster in obese than in normal subjects. In view of these kinetic defects in peripheral insulin action and of the fact that insulin is normally secreted in a phasic manner after meals, we postulated that the hyperinsulinemia of obesity does not compensate for insulin resistance and that the abnormal kinetics of insulin action in obesity are functionally important. To test this hypothesis, oral glucose tolerance tests (OGTTs) were performed in five control (mean age, 33 ± 2 yr) and five obese (mean age, 41 ± 5 yr) subjects. All controls had normal glucose tolerance; two obese subjects had normal and three had impaired glucose tolerance. After the results of the OGTTs were available, euglycemic clamp studies were performed in which insulin was infused in a phasic stepped fashion to mimic the rise and fall of mean peripheral insulin levels during the OGTTs. Each subject was clamped at both the “normal” and “obese” OGTT insulin profiles. During the OGTT, glucose and insulin levels were significantly elevated in the obese subjects compared with controls. Insulin-stimulated glucose disposal rates and total incremental glucose disposal (IGD) over 4 h were markedly reduced in obese compared with control subjects at the lower (normal) insulin-infusion profile (3 ± 1 vs. 41 ± 5 g, P < .001) and at the higher (obese) insulin-infusion profile (15 ± 4 vs. 72 ± 6 g, P < .001). Furthermore, during the normal insulin profile in controls compared with the obese insulin profile in obese subjects, IGD was still significantly reduced in the obese subjects (41 ± 5 vs. 15 ± 4 g, P < .001). At the lower as well as the higher insulin infusion, suppression of hepatic glucose output was not significantly different between obese and control subjects, as assessd by analysis of variance. In conclusion, our data demonstrate three important points. 1) Kinetic defects in the onset and decay of peripheral insulin action are functionally important in obesity when insulin is infused to match the physiological rise and fall of OGTT insulin levels. 2) Postprandial hyperinsulinemia in obesity only partially compensates for the peripheral insulin resistance. 3) The relative postprandial hyperglycemia in obesity may promote glucose disposal via the mass action of glucose and may be an important compensatory factor serving to normalize peripheral glucose disposal in insulin-resistant obese subjects.

Somatostatin Does Not Increase Insulin-Stimulated Glucose Uptake in Humans

Somatostatin (SRIF) has been widely used in the study of in vivo carbohydrate metabolism to suppress pancreatic hormone secretion and thereby interrupt the glucoregulatory feedback loops between insulin, glucagon, and glucose. A critical assumption in the use of SRIF is that it has no effect on hepatic or peripheral glucose metabolism other than those mediated through the inhibition of hormone secretion. To assess whether doses of SRIF commonly used in human investigation have any effect on insulin-stimulated glucose disposal rates, we measured 5 ± the rate in 6 normal subjects (mean fasting serum glucose level, 93 ± 2 mg/dl) during euglycemic (≃85 mg/dl) hyperinsulinemic (40 mU · m−2 · min1) clamp studies both with and without the concomitant infusion of SRIF (600 μg/hr). The steady-state insulin levels achieved were 85 ± 6 μU/ml and 74 ± 8 (μU/ml with and without SRIF, respectively (difference not significant). Glucose disposal rates between 120 and 180 min of the clamp were 7.11 ± 0.10 and 7.35 ± 0.10 mg · kg1 · min1 with and without SRIF, respectively (difference not significant). We concluded that in doses commonly used in human investigation, SRIF does not increase glucose disposal.