Biomedical subjects
Publications and source records attributed to J E Foley.
This study was performed to determine whether puromycin effects sugar transport into isolated rat adipocytes. Time-course and kinetic studies demonstrated that puromycin competitively inhibited 3-O-methylglucose transport. The data indicate that there is an acute effect of puromycin on sugar transport via competitive inhibition that is independent of the inhibition of protein synthesis.
The effects on adipocyte metabolism of increasing daily caloric intake by approximately 60% for 14 days was studied in seven nondiabetic moderately obese southwestern Native American Indians. Mean body weight increased by 3.0 +/- 0.3 kg, without any change in average size of isolated abdominal adipocytes. Overfeeding resulted in a 58% increase (P less than 0.01) in mean fasting plasma insulin concentration, whereas fasting plasma glucose concentration remained constant. Basal and maximum (8 nmol/L) insulin-stimulated glucose transport rates by isolated adipocytes increased by 83% (P less than 0.02) and 110% (P less than 0.01), respectively, after overfeeding, associated with an increase of 118% (P less than 0.01) in the incremental response to maximal insulin stimulation. However, no differences in either the sensitivity (ED50 of insulin for the stimulation of glucose transport) or the responsiveness (percent stimulation by insulin) of glucose transport were seen in isolated adipocytes as a result of overfeeding. Maximum insulin-stimulated total glucose utilization rates by isolated adipocytes incubated at 5.5 mmol/L glucose were 63% greater after overfeeding, due to increases in lactate formation, triglyceride synthesis, and CO2 production. Mono125I-(Tyr A14)-insulin binding per cell and per cell surface area was similar before and after overfeeding. The lipolytic rate of isolated adipocytes, in the absence and presence of 25 nmol/L and 2 mumol/L isoproterenol, was decreased by 75% (P less than 0.02), 45% (P less than 0.05), and 27% (P less than 0.05), respectively, after overfeeding. However, overfeeding did not result in a significant difference in the sensitivity of antilipolysis to insulin.(ABSTRACT TRUNCATED AT 250 WORDS)
The insulin clamp technique, which is often assumed to measure the ability of insulin to stimulate glucose uptake, actually measures both insulin-independent and insulin-dependent glucose uptake. In contrast, the minimal model technique, recently introduced by Bergman, Philips and Cobelli (1981), attempts to directly estimate insulin sensitivity (insulin-dependent glucose uptake = S1) by measurement of plasma glucose and insulin values during a 3 hour intravenous glucose tolerance test (IVGTT). In the present study estimates of insulin action derived from the insulin clamp and the minimal model technique were compared in 20 humans with varying degrees of glucose tolerance. The insulin response during the IVGTT was too low to permit calculation of S1 in 5 subjects - 4 with Type II diabetes and 1 with normal glucose tolerance. Although the correlation coefficient between the two tests in the other 15 patients was statistically significant (r = 0.53, P less than 0.05), this statement is somewhat misleading. Thus, S1 in the 4/7 patients with Type II diabetes in whom it could be measured was zero, and the correlation between estimates of insulin action with the two techniques in the 11 non-diabetic patients was not statistically significant (r = 0.41, P = NS) when these 4 patients were removed from the analysis. In conclusion, these data indicate that there was only a weak correlation between estimates of insulin action assessed with the insulin clamp and the minimal model techniques. One explanation for this observation is that the insulin-independent component of total glucose disposal both varies widely among patients and contributes significantly to glucose uptake as assessed by the insulin clamp technique.(ABSTRACT TRUNCATED AT 250 WORDS)
Basal and maximally insulin-stimulated Na+-pump activity was measured in adipocytes from subjects with normal glucose tolerance over a range of body mass indexes (BMI). In a comparison of 13 lean (BMI less than 25) vs. 15 extremely obese (BMI greater than 40) subjects basal activities per unit surface area were similar, but the maximally insulin-stimulated activity was significantly reduced in the extremely obese group [9.2 +/- 0.6 vs. 12.1 +/- 1.0 (min X dam2)-1, P less than 0.05]. The mean percent insulin stimulation of the Na+ pump above basal activity was 48 +/- 7% for the lean compared with 14 +/- 2% for the extremely obese group (P less than 0.001). A similar relationship was observed in these subjects for glucose transport where basal activities per unit surface area again were similar but the maximally insulin-stimulated transport was reduced in the extremely obese subjects (2.2 +/- 0.3 vs 5.1 +/- 0.6 attol/um2 X s, P less than 0.001). These results indicate that alterations in Na+-pump activity may be a manifestation of the insulin-resistant state that could contribute to the development of obesity via decreased cellular thermogenesis.
This study was initiated to compare the abilities of two alternative approaches to the measurement of insulin-dependent glucose disposal in normal humans. The ability of insulin to stimulate glucose disposal was measured in 12 normal subjects by determining glucose disposal rates during insulin clamp studies carried out at both basal insulin concentrations (approximately 6 microU/ml) and during a period of sustained hyperinsulinemia (approximately 60 microU/ml). The increment in glucose disposal was defined as insulin-dependent disposal and compared to estimates of insulin action generated by both the conventional insulin clamp approach and the minimal model technique. The results documented an extremely close correlation (r = 0.99; P less than 0.001) between the direct determination of insulin-dependent glucose disposal and insulin-stimulated glucose disposal as estimated by the insulin clamp technique. In contrast, there was a poor correlation (r = 0.44; P = NS) between insulin sensitivity as estimated by the minimal model technique and insulin-dependent glucose disposal. These results indicate that the value of glucose disposal determined by the insulin clamp approach, which includes both insulin-independent and insulin-dependent glucose disposal, provides an excellent estimate of insulin-dependent glucose disposal in subjects with normal glucose tolerance. Unfortunately, this does not appear to be true of the minimal model technique. However, it must be emphasized that these conclusions are only applicable to normal humans, and may not apply to normal subjects of other species or to humans under different physiological or pathological situations.
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This study was undertaken to determine whether glucose 6-phosphate can modulate hexose transport in rat adipocytes. The data demonstrated that glucose 6-phosphate decreased hexose transport rates in adipocytes and in adipose plasma membrane vesicles. This effect was not via competitive inhibition. The data provide direct evidence that hexose transport can be inhibited noncompetitively by glucose 6-phosphate.
The in vitro sensitivities of glucose transport and antilipolysis to insulin and insulin binding were measured in adipocytes isolated from three groups of normal glycemic male Pima Indians--10 lean (11% to 22% body fat), 11 moderately obese (26% to 34% body fat), and 7 severely obese (37% to 40% body fat) subjects. Both a half-maximum concentration of insulin for the stimulation of glucose transport (ED50 [transport]) and a half-maximum concentration of insulin for the suppression of 25 nmol/L isoproterenol-stimulated lipolysis (ED50 [antilipolysis]) were significantly (P less than 0.05) greater in the moderately obese subjects than in the lean subjects as well as greater in the severely obese group than in the moderately obese group. Mono 125I-(Tyr A14)-insulin binding per cell in the presence of 25, 100, and 200 pm insulin was similar among lean, mildly obese, and severely obese subjects. 125I-insulin binding per cell surface area of adipocytes isolated from either moderately or severely obese Indians was significantly lower (P less than 0.005) than that of lean Indians. However, there was a similar insulin binding per cell surface area between mildly and severely obese subjects. These results indicate that diminished insulin binding per cell surface area may explain decreased sensitivity of transport and antilipolysis to insulin in moderately obese subjects relative to lean subjects. In contrast, these diminished sensitivities in the severely obese subjects relative to moderate obese subjects are not explained by a change in insulin binding and, therefore, are presumably induced by an abnormality of a postbinding step of insulin action.
In an effort to determine whether differences in basal and maximum insulin-stimulated glucose transport by isolated adipocytes are a function of donor sex, we measured glucose transport rates in the absence and presence of 8 nM insulin in adipocytes isolated from the abdominal subcutaneous fat tissue of nine male and ten female subjects with varying degrees of obesity and in adipocytes isolated from the abdominal subcutaneous and retroperitoneal fat tissue of (180-220 g) male and female rats. Because maximal insulin-stimulated glucose transport rate per cell of adipocytes isolated from subcutaneous abdominal tissue of male and female subjects was constant in each sex, the data have been normalized on the basis of transport per cell. The results demonstrated that basal and maximal insulin-stimulated glucose transport per cell was 53-75% higher per cell in the females versus males in adipocytes from human subcutaneous abdominal adipose tissue (P less than 0.01). A similar difference in glucose transport rate between males and females (P less than 0.001) was also found in rat abdominal subcutaneous adipose tissue. Adipocytes isolated from rat retroperitoneal adipose tissue had higher transport rates (approximately three-fold) and smaller sex differences (35% higher in females) than found in adipocytes from rat and human subcutaneous tissue. These results indicate that basal and maximum insulin-stimulated glucose transport is higher by adipocytes isolated from females and that this difference is independent of adipose cell size and species.
Previous studies have left unanswered whether human obesity, independent of glucose intolerance, is associated with a "postreceptor" defect in insulin action. We have studied the relationship between the degree of obesity (as estimated by underwater weighing) and the maximal insulin-stimulated glucose disposal rate (M) in vivo in 52 glucose-tolerant Pima Indian males. The relationship was examined independently of differences in age and maximal oxygen uptake (an estimate of "physical fitness"). The maximal insulin-stimulated glucose transport rate (MTR) was also measured in isolated abdominal adipocytes from the same subjects to determine whether differences in M could be explained by differences in glucose transport. The results showed that there was a large variance in M and MTR among these glucose-tolerant subjects. M was better correlated with glucose storage rates than with oxidation rates, as estimated by indirect calorimetry. The most obese subjects had only a 20% lower mean M and 30% lower MTR than the most lean subjects. The lower M in the obese subjects was due to both lower glucose oxidation and storage rates. There was no significant, independent correlation between age or degree of obesity and M or MTR. The maximal oxygen uptake (VO2 max) appeared to independently account for 20% of the variance observed in M. MTR was only weakly correlated with M (r = 0.36, P less than 0.02). We concluded that differences in M in these glucose-tolerant subjects must be explained by factor(s) other than maximal oxygen uptake, age, maximal insulin-stimulated glucose transport in vitro, or degree of adiposity per se.
To examine the effect of a four-day fast on neutral glyceride mobilization in human adipocytes, subcutaneous abdominal fat tissue was obtained from ten human volunteers after an overnight fast and then after four days of fasting. Plasma insulin concentration decreased from 31 +/- 5 microU/ml before the four-day fast to 9 +/- 1 microU/ml after the fast (P less than 0.05). Plasma free fatty acid concentration increased from 13.9 +/- 1.3 to 23.6 +/- 3.2 mg/dl (P less than 0.05). Mean average cell size was similar before and after the four-day fast. Basal lipolysis increased threefold (P less than 0.005) regardless of cell size after four days of fasting. In contrast, isoproterenol (2 microM) stimulated maximum lipolysis was not increased after a four-day fast. The concentrations of isoproterenol required for a half maximum stimulation in the presence of 50 (7 microU/ml) and 8000 pM (1150 microU/ml) insulin were lower after a four-day fast (P less than 0.05, P less than 0.03, respectively) and were uninfluenced by average cell size. Basal and maximum insulin-stimulated glucose transport were similar after a four-day fast. However, glucose incorporation into neutral glycerides was reduced by 50 percent (P less than 0.02) following a four-day fast. The reduction was uninfluenced by average cell size. The data indicate that abdominal adipocytes after a four-day fast are metabolically adapted towards increased neutral glyceride mobilization by reducing glucose incorporation into neutral glycerides, increasing sensitivity of lipolysis to isoproterenol, and increasing basal lipolysis.
The regulation of glucose transport by a beta-adrenergic agonist and other cAMP stimulators was assessed by kinetic analyses of 3-O-methylglucose (MG) transport in rat and human adipocytes and in isolated rat plasma membrane vesicles. Basal MG transport was biphasically affected by L-isoproterenol in rat adipocytes: lower concentrations (10-25 nM) of L-isoproterenol stimulated the basal rate by increasing the Vmax, but higher concentrations (0.5-2 microM) of L-isoproterenol inhibited the basal rate. On the other hand, the maximum insulin-stimulated MG transport rate was not affected by 25 nM L-isoproterenol, but was suppressed by 2 microM L-isoproterenol in rat adipocytes. In the presence of adenosine deaminase plus L-isoproterenol (25 nM and 2 microM), dibutyryl cyclic AMP (Bt2cAMP), 3-isobutyl-1-methylxanthine, or forskolin, both basal and the maximum rates of MG transport were suppressed in rat adipocytes. However, from kinetic experiments, both L-isoproterenol plus adenosine deaminase and Bt2cAMP decreased the Vmax. On the other hand, isobutymethylxanthine and forskolin decreased the Vmax as well as increased the K8. MG transport in plasma membrane vesicles was directly inhibited by either forskolin or isobutylmethylxanthine. In contrast, both 25 nM and 2 microM L-isoproterenol with or without adenosine deaminase, Bt2cAMP, or cAMP had no effect on MG transport in rat plasma membrane vesicles. In human adipocytes, L-isoproterenol always stimulated basal MG transport and did not suppress the maximum rate of MG transport, even though cAMP production was maximally stimulated by L-isoproterenol. Both adenosine deaminase plus L-isoproterenol and Bt2cAMP did not suppress the basal rate, but did show a modest suppression (40%) of the maximum insulin effect on MG transport in human adipocytes. However, both isobutylmethylxanthine and forskolin remarkably suppressed (85%) both the basal and the maximum rate of MG transport by both increasing the K8 and decreasing the Vmax. These results indicate MG transport in both rat and human adipocytes is regulated by 3 different mechanisms: (I) L-isoproterenol, a beta-adrenergic agonist, stimulates basal MG transport by increasing the Vmax, (II) cAMP mediates a decrease in MG transport by decreasing the Vmax, and (III) both forskolin and isobutylmethylxanthine also decrease MG transport by directly inhibiting the binding of MG molecules to transporters, resulting in a decrease in the Vmax and an increase in the K8.
To assess possible cellular mechanisms of in vitro resistance in noninsulin-dependent diabetes mellitus (NIDDM), maximum insulin-stimulated glucose transport and utilization and insulin binding were measured in adipocytes isolated from weight-matched normal glycemic subjects and patients with NIDDM. Glucose transport rate was determined by measuring the amount of [U-14C]-D-glucose taken up by incubating adipocytes at trace concentrations of glucose (300 nM), and glucose metabolism by estimating the amount of lactate, CO2, triglyceride, and total glucose carbons retained in the cells following incubating at 5.5 mM glucose. Insulin binding was measured at 50, 100, and 200 pM [mono125I-tyrosinyl A14]insulin. Both maximum insulin-stimulated glucose transport and utilization in adipocytes from diabetic subjects were 40% (P less than 0.01) and 32% (P less than 0.05) lower, respectively, than values obtained for subjects with normal glucose tolerance. In addition, the maximum capacity of glucose transport was correlated with the maximum capacity of glucose utilization (r = 0.81, P less than 0.001). Furthermore, fasting plasma glucose concentrations of diabetic subjects were negatively correlated with both maximum insulin-stimulated glucose transport (r = -0.56, P less than 0.05) and glucose utilization (r = -0.67, P less than 0.05). Since basal glucose transport in adipocytes from diabetic subjects was also 33% lower than in adipocytes from normal subjects, there was no change in the relative ability of insulin to stimulate glucose transport. However, there was a 64% decrease in the sensitivity of the glucose transport system to insulin (P less than 0.05), unrelated to concomitant changes in insulin binding. These results demonstrate that both maximal insulin-stimulated glucose transport and utilization, and the sensitivity of the glucose transport system to insulin, was decreased in adipocytes isolated from subjects with NIDDM. These in vitro defects were associated with impaired glucose metabolism in vivo, consistent with the view that the metabolic alterations observed at the cellular level may contribute to the in vivo insulin resistance of NIDDM.
It has been previously reported that maximum insulin-stimulated glucose transport and utilization were both decreased, while basal lipolysis was increased in adipocytes from obese subjects with noninsulin-dependent diabetes mellitus (NIDDM). To determine whether these values can be returned towards those obtained in equally obese subjects with normal glucose tolerance, these measures of adipocyte metabolism were quantified in 10 NIDDM subjects before and after control of hyperglycemia with insulin. The results demonstrate that maximum insulin-stimulated glucose transport (P less than 0.02) and glucose incorporation into triglyceride (P less than 0.01) and CO2 (P less than 0.05) (at 5.5 mM glucose) increased and basal lipolysis decreased (P less than 0.05) after 4 wk of insulin treatment. In contrast, glucose incorporation into lactate and other glycolytic metabolites (at 5.5 mM glucose), and sensitivity of glucose transport to insulin, did not improve with insulin therapy. The latter occurred despite an increase in insulin binding (P less than 0.01). Finally, the improvement in maximal insulin-stimulated glucose transport correlated with the fall in fasting hyperglycemia (r = 0.77, P less than 0.01). These findings demonstrate that several of the abnormalities of carbohydrate and lipid metabolism recently noted to be present in adipocytes from patients with NIDDM can be shown to significantly improve with insulin treatment.
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After a 7-day lead-in period, one of three beta-adrenergic antagomists was taken for 2 wk by 10 healthy male subjects. The drugs were metoprolol (cardioselective) and propranolol and nadolol (both nonselective). Dosage was according to currently recommended regimens and was increased after the first week (50 to100 mg b.i.d., 20 to 40 mg q.i.d., and 80 to 160 mg q.d.). Pulmonary mechanics and density dependence (DD) of maximal expiratory flow were measured before and at the end of the placebo lead-in period and the low- and high-dose treatment weeks. Total lung capacity (TLC), residual volume (RV), and RV/TLC all rose (P less than 0.05) after high-dose nadolol. Forced vital capacity (FVC) and expiratory reserve volume fell (P less than 0.05) after high-dose nadolol. Forced vital capacity (FVC) and expiratory reserve volume fell (P less than 0.05) after high-dose metoprolol. There was no change in forced expiratory volume in 1.0 sec (FEV1), FEV1/FVC, maximal midexpiratory flow rate, or airway resistance with any of the beta-antagonists. Decreases (P less than 0.05) in maximal expiratory flow determined at 50% of the vital capacity occurred after propranolol and metoprolol, but not after nadolol. A dose-related decrease in DD at 50% of the vital capacity accompanied nadolol dosing, but was significant only after the high-dose regimen. The decreases in DD with nadolol, as well as its effect on RV/TLC, are consistent with small airway narrowing. The findings with metoprolol and propranolol suggest that they affect central as well as peripheral airways.
The effects of increasing cell size on glucose transport activity and metabolism and on the concentrations of glucose transport systems in both the plasma and low density microsomal membranes in isolated adipose cells from the aging rat model of obesity have been examined. Glucose transport activity was assessed by measuring l-arabinose transport and the concentration of glucose transport systems estimated by measuring specific d-glucose-inhibitable cytochalasin B-binding. Basal glucose transport activity increases from 0.3 to 1.4 fmol/cell/min with a 10-fold increase in cell size, but remains constant per unit cellular surface area and is accompanied by a constant 5 pmol of glucose transport systems/mg of membrane protein in the plasma membrane fraction. Maximally insulin-stimulated glucose transport activity, on the other hand, remains constant at 2.3 fmol/cell per min with increasing cell size, but markedly decreases per unit cellular surface area and is accompanied by a decrease from 30 pmol of glucose transport systems/mg of plasma membrane protein to the basal level. These diminished effects of insulin on glucose transport activity and the number of glucose transport systems in the plasma membrane fraction in enlarged cells are paralleled by an 80% decrease in the basal number of glucose transport systems/mg of membrane protein in the low density microsomal membrane fraction, the source of those glucose transport systems appearing in the plasma membrane in response to insulin. The effects of cell size on the metabolism of a low concentration of [1-(14)C]glucose (0.56 mM) directly parallel those on glucose transport activity and the concentration of glucose transport systems in the plasma membrane fraction, and are not associated with significant alterations in the cell's sensitivity to insulin. Thus, adipose cellular enlargement is accompanied by the development of a marked "insulin resistance" at the glucose transport level, which may be the consequence of a relative depletion of glucose transport systems in the intracellular pool.