Buris R. Boshell

Lactate Turnover and Gluconeogenesis in Normal and Obese Humans: Effect of Starvation

Turnover rates of lactate and glucose were determined in normal, obese, and fasted obese human subjects. L—(+) lactate-U-C-14 (50μc.) and glucose-l-C-14 (50 μc.) were administered over a four-hour period on consecutive days by a primed-infusion technic. Lactate and glucose interconversion rates were calculated from precursor-product specific activity ratios obtained during the infusion period and the rates of lactate and glucose turnover. Glucose turnover, oxidation, recycling, and conversion to lactate, when expressed on a mg./kg./hr. basis, were significantly less in obese subjects than in normals; however, when expressed as a percentage of the turnover, no significant differences were observed. Glucose oxidation represented 14 per cent; recycling, 10 per cent; and conversion to lactate, 66 per cent of the glucose turnover rate. Approximately 15 per cent of the glucose turnover was derived from lactate. In contrast, there were no significant quantitative or qualitative differences in the metabolism of lactate by normal or obese subjects. Lactate oxidation represented 11 per cent and lactate conversion to glucose 21 per cent of the lactate turnover rate. During starvation, there was a 30 per cent reduction in glucose pool size, turnover, and oxidation. Blood lactate concentrations and lactate turnover were unchanged despite decreased conversion of glucose to lactate. The conversion of lactate to glucose increased from 14 ± 2 to 21 ± 2 mg./kg./hr. and represented 36 per cent of the lactate turnover. The fraction of the glucose turnover derived from lactate increased two-fold, from 17 to 38 per cent. These results are in general agreement with those obtained in animals and are the first quantitative estimates of lactate-glucose interconversion rates in man. The combination of decreased glucose conversion to lactate and increased lactate conversion to glucose in the presence of an unchanged blood lactate concentration and turnover requires that there be increased synthesis of lactate from sources other than glucose. In addition, increased conversion of lactate to glucose at unchanged blood concentrations indicates enhanced extraction of lactate during starvation.

Lactate turnover and gluconeogenesis in obesity. Effect of phenformin.

The effect of phenformin on the rates of lactate and glucose turnover, interconversion, and oxidation was determined in five obese subjects with normal glucose tolerance. L (+) lactate-U (50 μc.) and glucose 1-C-14 were administered over four-hour periods on consecutive days by a primed infusion technic. One hundred to 150 mg. of phenformin was administered daily, and the turnover studies were repeated on the sixth and seventh days of therapy. Phenformin increased glucose turnover by 10 per cent, from 95.6 ± 4.4 to 106.2 ± 4.7 (mean ± S.E.M.) mg,/kg./ hr. and glucose recycling by 100 per cent, from 8.7 ± 1,4 to 19.3 ± 1.3 mg./kg./hr. In contrast, the changes in glucose oxidation were inconsistent, decreasing in three subjects and increasing in two. As expected, the blood glucose concentration and glucose pool were unchanged during treatment with phenformin. Lactate turnover increased 30 per cent, from 63.5 ± 3.5 to 82.8 ± 5.7 mg./kg./hr., and lactate derived from glucose (glucose conversion to lactate) increased 25 per cent, from 57.9 ± 5.5 to 71.8 ± 6.9 mg./kg./hr. Lactate conversion to glucose increased in all subjects by a mean of 13.1 ± 1.2 mg./kg./hr., from 15.2 ± 1.2 to 28.2 ± 1.8 mg./kg./hr. The increase in lactate conversion to glucose was almost identical to the increase in glucose turnover and glucose conversion to lactate. During therapy with phenformin, 34.1 ±1.2 per cent of the lactate turnover was converted to glucose in contrast to 22.1 ± 1.3 per cent before therapy. These results demonstrate that phenformin enhances the interconversion of glucose and lactate in subjects in whom it exerts no hypoglycemie effect.

Etiological Factors in Thiazide-induced or Aggravated Diabetes Mellitus

Nine patients with diabetes mellitus and three normal controls were treated for one week with hydrochlorothiazide (150 mg. per day), and certain effects on carbohydrate metabolism were observed. Evidence presented in this study confirms the thiazide-induced carbohydrate intolerance. Tests of insulin reserve (serum ILA response to glucose), response to insulin, insulin binding, urinary steroid excretion, serum potassium, serum nonesterified fatty acids, and serum amylase failed to reveal any abnormality related to the carbohydrate intolerance. There was reduction of the whole blood glutathione levels in six of seven subjects. DIABETES 14:132–36, March 1965.

Biochemistry of Extrapancreatic Tumor Hypoglycemia

To define the biochemistry of tumor hypoglycemia, the metabolism of glucose and lactate were investigated in a patient with hypoglycemia associated with an adrenocortical carcinoma. Glucose and lactate kinetics and interconversion were determined by a primed-infusion technic in which 100 μc. each of glucose-1 and L-(+) lactate-U-C-14 were administered over a four-hour period on successive days before and after removal of the tumor. Before removal of the tumor, 400 gm. of glucose per day were required to maintain normoglycemia. Glucose turnover and its conversion to lactate were increased to values that were two to three times those observed in five normal subjects studied by these technics. Glucose oxidation and its contribution to the fuel of respiration were also enhanced. Although all aspects of glucose metabolism were quantitatively increased, no single route of glucose disposal was responsible for the accelerated turnover, and the pattern of metabolism was qualitatively normal. Despite excessive cortisol production, endogenous glucose production was paradoxically suppressed to 20 per cent of normal, and lactate incorporation into glucose was inhibited. Plasma free fatty acid concentrations were normal but did not respond to the administration of epinephrine. Following surgery, the hypoglycemia disappeared, glucose and lactate turnover returned to normal, and gluconeogenesis from lactate increased. Immunoreactive insulin and insulin-like activity in the plasma were not increased and extracts of the tumor did not produce hypoglycemia when injected into mice. The hypoglycemia in this patient was due to a combination of increased glucose utilization and decreased glucose production. The data are consistent with the concept that these tumors synthesize and release a substance, which is currently unidentified, which acts on peripheral tissues and liver in a manner similar to insulin but which is undetectable by immuno- and bioassay technics.

INSULIN RESISTANCE. RESPONSE TO INSULIN FROM VARIOUS ANIMAL SOURCES, INCLUDING HUMAN.

The comparative usefulness of crystalline human, porcine, dealaninated porcine and bovine insulin in the treatment of insulin resistance was studied. A series of normals, insulin-sensitive diabetics, and insulin-resistant diabetics received various types of insulin in acute intravenous tolerance tests. The insulin-resistant patients were far less responsive to all forms of insulin in these tests than were the normals and insulin-sensitive diabetic patients. No positive correlation was found between responsiveness to a particular type of insulin in an acute tolerance test and responsiveness during a prolonged clinical trial. Seven patients with insulin resistance received clinical trials with at least one insulin other than bovine. Three of these patients were found to be more sensitive to either human, porcine or dealaninated porcine than to bovine insulin. Insulin binding capacities of sera from the responsive patients were somewhat higher than the binding capacities of the nonresponders. The insulin binding capacities of sera from the responsive patients were just as high or higher for the insulin to which the patient responded as they were for bovine insulin. Serum from the responsive patients in general antagonized added porcine, dealaninated porcine and bovine insulin to the same degree in vitro. Adipose tissue from the responders was no more sensitive to human or porcine than to bovine insulin in vitro. The increased sensitivity of these patients to insulin from a nonbovine source may be due to a difference in kinetics of the antigen-antibody reaction in vivo which is not demonstrable in vitro. Patients with obesity and insulin resistance responded to a reducing diet. Three of four such patients placed on 600 to 900 calorie diets lost their need for insulin over a fourto six-week period.

Effect of Pancreatic Proteins on Insulin Assay Systems

The following proteins were analyzed for insulin-like behavior in the rat hemidiaphragm, rat fat pad, and two antibody immunoassay systems: ribonuclease A, deoxyribo-nuclease I, alpha-chymotrypsin, chymotrypsinogen A, tryp-sin, and trypsinogen. Chymotrypsin stimulated glucose uptake in the rat hemidiaphragm and behaved like insulin in the immunoassay system when the enzyme concentration was 7 × 10-6 M. No similar activity was found for any of the other proteins. Chymotrypsin was inactive at lower concentrations. The stimulation of glucose uptake in the rat hemidiaphragm by chymotrypsin was not prevented by the presence of guinea pig anti-insulin serum. This and other evidence suggests that the enhanced uptake of sugar is not due to insulin contamination and is probably a result of partial proteolysis of cell membrane with resulting increase in permeability. Mixtures of chymotrypsin with guinea pig anti-insulin serum and 1-131-labeled insulin under the conditions of the immunoassay were analyzed electrophoretically, and the results indicate partial hydrolysis of the labeled insulin. This hydrolysis probably accounts for the apparent insulin response produced by chymotrypsin in the two antibody immunoassay system.

Acetohexamide: comparison with other sulfonylurea compounds in the treatment of diabetes mellitus.

A new oral hypoglycemic agent, acetohexamide, is compared with four other sulfonylurea drugs in 70 patients with diabetes mellitus, the majority of whom had had either primary or secondary failure with other oral hypoglycemic compounds.

Free and total insulin levels in a patient with insulin-resistant diabetes mellitus and chronic lymphatic leukemia: Effect of prednisone therapy

An insulin-resistant diabetic patient who also has chronic lymphocytic leukemia and very high plasma levels of free and total insulin along with high levels of insulin antibodies is described. In response to prednisone therapy, his insulin requirement decreased, but the total and free insulin concentrations increased as insulin antibody measured as the maximal insulin-binding capacity of plasma remained unchanged. In insulin resistance, persistent hyperglycemia, in spite of high levels of immunoreactive free insulin, presumably reflects peripheral tissue unresponsiveness to insulin. The beneficial effect of prednisone treatment in this patient is discussed, and it is postulated to be the result of either increased availability of free insulin or an increased responsiveness of the tissues to insulin or both.