Stabilization of alpha-ketoisocaproic acid in serum and plasma.
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Drug Stability↗
Biomedical subjects
S C Kalhan
Publications and source records attributed to S C Kalhan.
Vasoactive intestinal polypeptide potentiates the hypoxemia-induced decrease in splanchnic circulation in the rat.
The effects of acute infusion of vasoactive intestinal polypeptide (VIP) and hypoxemia on splanchnic circulation were examined in 35 awake Sprague-Dawley rats. Indwelling catheters were placed in the superior vena cava and the proximal aorta via the internal jugular vein and internal carotid artery, respectively, while the rats were under ether anesthesia. Four hours later, when the rats were awake and active, VIP (molecular lot 3226) was infused intraarterially for 30 minutes. The distribution of cardiac output was measured at the end of VIP infusion using 125I-labeled microspheres. VIP was administered at a low (1.5 ng/min) and a high infusion rate (44.1 ng/min) for 30 minutes. The effect of hypoxemia on circulatory response to VIP was examined only in the high VIP infusion group, by placing the rat in a 10% oxygen environment. Appropriate control experiments were performed with each group. The high-dose VIP resulted in a marked reduction in distribution of cardiac output to the splanchnic circulation. This effect was potentiated by hypoxemia, particularly in the distal ileum and colon. The metabolic clearance rate of VIP increased with the rate of VIP infusion and was decreased by hypoxemia. It was concluded that only in high concentration does VIP have any effect on splanchnic circulation. However, in the presence of hypoxemia, VIP may have an important role in cardiovascular compensatory response and may contribute to the development of ischemic bowel injury.
Animals↗
Glucose-alanine relationship in normal human pregnancy.
In order to quantify the glucose-alanine relationship in normal human pregnancy, the turnover rates of alanine and the incorporation of alanine carbon into glucose were quantified in 15 pregnant women during the last 4 weeks of gestation following a ten-hour fast. Eight nonpregnant women of similar age group were studied as controls. L-[2,3-13C2]Alanine and D[6,6-2H2]glucose were infused as tracers. The 13C enrichment of alanine, lactate, and glucose and the deuterium enrichment of glucose were measured by gas chromatography-mass spectrometry. In five pregnant and five nonpregnant women, the contribution of alanine carbon to expired CO2 directly and via glucose was estimated by combining indirect respiratory calorimetry with the tracer infusions. The alanine turnover rates in the pregnant and nonpregnant women were similar (pregnant, 4.43 +/- 0.82 mumol/kg x min; nonpregnant, 4.11 +/- 1.08 mumol/kg x min, mean +/- SD). However, the fraction of alanine incorporated into glucose was significantly lower during pregnancy (23.5 +/- 8.3% v 30.8 +/- 8.2%, P less than .04). In pregnant women, 20% of lactate pool was derived from alanine as compared with 28% in nonpregnant subjects (P less than .02). Twenty-four percent of alanine turnover was converted to CO2 in both pregnant and nonpregnant women. The plasma insulin concentration was increased significantly during pregnancy (P less than .05). These data suggest that gluconeogenesis from alanine is attenuated during pregnancy. This decrease in gluconeogenesis is not the result of decreased alanine flux, but due to intrinsic intrahepatic mechanism such as decreased deamination of alanine mediated by the predominant insulin effect or a decreased hepatic uptake of alanine.(ABSTRACT TRUNCATED AT 250 WORDS)
Adult↗
Effects of maternal glucose infusion on fetal acid-base status in human pregnancy.
The maternal and fetal metabolic effects of three commonly used intravenous fluids administered before regional anesthesia were studied in 32 gravid women undergoing elective cesarean section at term. Patients were randomized into one of three groups to receive 1 L of either 5% dextrose (50 gm of glucose) or Ringer's lactate or isotonic saline solution before epidural anesthesia. Acute glucose infusion resulted in maternal hyperglycemia, hyperinsulinemia, and an increase in the blood lactate level. Cord blood glucose, insulin, and lactate levels were also increased in this group. The key finding of this study was the significant lowering of pH in the umbilical cord vein (7.31 +/- 0.04) and artery (7.21 +/- 0.06) in the glucose-infused group when compared with the non-glucose infusion groups (p less than 0.05). Confounding perinatal factors such as maternal position, maternal hypotension, and prolonged time of surgery did not influence the fetal acid-base status. Thus acute maternal glucose infusion in normal patients can cause fetal hyperglycemia, metabolic acidosis, and neonatal hypoglycemia. These findings may be of particular clinical importance when fetal distress or fetal hypoxemia is due to other perinatal events. Under these circumstances, acute maternal glucose infusion may further contribute to fetal metabolic acidosis.
Acid-Base Equilibrium↗
Leucine metabolism in human newborns.
The present study was designed to 1) determine whether a relationship exists between newborn birth weight and leucine metabolism and 2) compare leucine and energy metabolism in a period of rapid growth and development (i.e., newborn) with a constant nongrowth period (i.e., adult). Leucine kinetics and energy expenditure were measured in the postabsorptive state in 12 normal full-term newborns in early neonatal life and in 11 normal adults using a primed constant L-[1-13C]leucine infusion combined with respiratory calorimetry. A significant positive correlation between newborn birth weight and leucine flux was observed. Leucine flux per kilogram body weight was significantly greater in newborns compared with adults, as was leucine oxidation and energy expenditure. When normalized to metabolic body weight (W0.75), newborns and adults had similar rates of energy expenditure, leucine flux, and oxidation. The allometric exponent relating leucine flux to body weight (0.80) was nearly equivalent to that describing the energy expenditure-to-body weight relationship (0.79) and both were similar to the 0.75 metabolic weight exponent. These data suggest the following. 1) A relationship exists between newborn birth weight and protein metabolism, as reflected by the correlation between leucine flux when expressed as micromoles per kilogram per hour and birth weight. It is speculated that this relationship may be the result of differences in previous protein and energy supplies. 2) The high rate of leucine flux measured in newborns probably reflects the rapid remodeling of protein that occurs in this period of development, even during fasting.(ABSTRACT TRUNCATED AT 250 WORDS)
Adult↗
Quantitation of branched-chain alpha-keto acids as their N-methylquinoxalone derivatives: comparison of O- and N-alkylation versus -silylation.
Quantitative estimation of isotopic enrichment and concentrations of keto analogs of branched-chain amino acids in biological fluid has been used for the study of protein metabolism in animal and human studies. At present, O-trimethylsilyl-quinoxalinol derivative is used widely in the quantification of branched-chain alpha-keto acids. In the present study, N-methyl-quinoxalone derivative was developed and its use in quantification in human studies verified. O-phenylenediamine and alpha-keto acid react in acidic media to yield phenolic and amide tautomers. O-trimethylsilyl-quinoxalinol derivative of the phenolic tautomer is used at present for quantification by chemical ionization/selected ion monitoring. We have prepared N-methyl-quinoxalone derivative using N,N-dimethyl formamide dimethyl acetal. This derivative is characterized by a major amide form and a minor phenolic form. The mass spectrum has a characteristic fragment, which facilitates easy identification and quantitation by electron impact/selected ion monitoring. Because m/z 174 was observed as the base peak for alpha-ketoisocaproate, alpha-keto-beta-methylvalerate and alpha-ketoisovalerate, "single ion monitoring' could be performed for the quantification of isotopic enrichment as well as plasma concentration of these three branched-chain alpha-keto acids. Isotopic enrichment from 0.25 to 7.5 at% excess could be measured easily, with an average coefficient of variation of less than 8%. Plasma concentrations as low as 10 microM l-1 in a 200-microliters aliquot could be measured. Methyl migration was an interesting feature of the mass spectrometric fragmentation pattern of the alpha-keto acids. The mechanism of methyl migration is proposed and discussed. This paper also describes some of the studies involved in the formation of isomeric O- and N-alkyl, -quinoxaline and -quinoxalone using a number of N,N-dimethyl formamide dialkyl acetals.
Alkylation↗
Immediate diagnostic criteria for bacterial infection of ascitic fluid. Evaluation of ascitic fluid polymorphonuclear leukocyte count, pH, and lactate concentration, alone and in combination.
We prospectively evaluated the ascitic fluid (AF) polymorphonuclear cell (PMN) count, pH, and lactate concentration in single ascitic fluids from 60 patients to determine their relative predictive values for the immediate diagnosis of ascitic fluid infection. Nine of the 60 ascitic fluids were malignant. Of the remaining 51 samples, nine from cirrhotic patients were infected. The mean AF pH, lactate concentration, and PMN count in the infected group were 7.20 +/- 0.19, 80 +/- 51 mg/dl, and 18,199 +/- 19,650 cells/mm3, respectively, and all were significantly different from the corresponding values in noninfected ascites. Mean arterial blood-ascitic fluid (B-AF) pH and lactate gradients in the infected group were 0.23 +/- 0.17 and -46 +/- 31 mg/dl, respectively, and were significantly different from the corresponding values in noninfected ascites (p less than 0.05). Significant differences were not found between infected and malignant ascites, except for the AF PMN count (p less than 0.001). In cirrhosis with ascites, an AF pH less than or equal to 7.34 was the most specific single test (100%) and had the highest diagnostic accuracy (98%). In the larger group of patients with ascites of diverse etiology, a B-AF pH gradient greater than or equal to 0.10 or an AF PMN count greater than or equal to 500 cells/mm3 were the single tests with the highest diagnostic accuracy (92%). Combining an AF PMN count greater than 500 cells/mm3 with any of the other diagnostic criteria increased the specificity and diagnostic accuracy (up to 98%) compared to the best single criterion. Although our data support the use of a number of different combinations of AF measurements for the immediate diagnosis of infection, the simplest and most readily obtainable measurements are the pH and PMN count. Therefore, in the clinical setting we recommend the use of either an AF pH less than or equal to 7.34 or a B-AF pH gradient greater than or equal to 0.10 in combination with an AF PMN count greater than 500 cells/mm3 to obtain the highest degree of accuracy in the immediate diagnosis of ascitic fluid infection.
Adult↗
Glucose carbon recycling and oxidation in human newborns.
Total carbohydrate oxidation, plasma glucose oxidation, and glucose carbon recycling were measured in 11 fasting newborns using a constant infusion of D-[U-13C]glucose combined with respiratory calorimetry. The "true" rate of glucose appearance (Ra) was quantified from the enrichment of the nonrecycling tracer species (m + 6), while the "apparent" rate of glucose appearance was quantified from the enrichment of glucose C - 1. The plasma glucose concentration remained constant at approximately 50 mg/dl (2.8 mM) throughout the study. The true rate of glucose production was 5.02 +/- 0.41 mg X kg-1 X min-1, (means +/- SD). Glucose was oxidized at a rate of 2.67 +/- 0.34 mg X kg-1 X min-1 and represented 53% of the glucose turnover. Recycling of glucose carbon represented 36% of the glucose production rate, or 1.87 +/- 0.74 mg X kg-1 X min-1. The oxidation of plasma glucose provided 15.8 +/- 2.0 kcal X kg-1 X day-1, whereas total carbohydrate oxidation (measured by respiratory calorimetry) provided 19.9 +/- 6.6 kcal X kg X day. The data indicate that 1) recycling of glucose carbon accounts for about one-third of glucose production, demonstrating active gluconeogenesis in the fasting newborn; 2) the oxidation of plasma glucose represents only 80% of total carbohydrate oxidation, the remaining 20% possibly representing the local oxidation of tissue glycogen stores; and 3) as the measured rate of glucose oxidation will be insufficient to supply the entire calculated cerebral metabolic requirements, these data suggest that fuels in addition to glucose may be important for cerebral metabolism in the fasting human newborn.
Blood Glucose↗
Role of glucose in the regulation of endogenous glucose production in the human newborn.
The role of plasma glucose concentration in the regulation of endogenous glucose production in the human newborn was examined by infusing glucose at 2.6-4.6 mg/kg . min as a continuous infusion to eight normal term appropriate for gestational age infants, five preterm, and six small for gestational age infants. All infants were healthy, had no overt clinical problems and were studied 6 h after their last feed. Glucose production rates were measured during the basal state and during glucose infusion by tracer dilution using [6,6(2)H2]glucose. The rate of glucose production during the basal state was similar in preterm and term appropriate for gestational age infants (appropriate for gestational age 3.53 +/- 0.32, preterm 3.49 +/- 0.38 mg/kg . min, mean +/- SD), while it was higher in the small for gestational age infants (4.25 +/- 0.98, p less than 0.03) as compared with appropriate for gestational age. During glucose infusion, the peak glucose concentration was related to the rate of glucose infusion. The endogenous glucose production rates during glucose infusion were variable in the three groups. However, a negative correlation between peak glucose concentration and endogenous glucose production rate was observed (r = 0.59, p = 0.006). The insulin response to glucose infusion was comparable in all infants. In addition, three small gestational age and one preterm infants, who had become hypoglycemic in the immediate newborn period, were studied while they were receiving parenteral glucose and their plasma glucose had stabilized at 55.5 +/- 10.25 mg/dl. Tracer kinetic studies showed persistence of endogenous glucose production in these infants even though they were receiving high rates of exogenous glucose infusion.(ABSTRACT TRUNCATED AT 250 WORDS)
Blood Glucose↗
Maternal obesity as a risk factor in gestational diabetes.
Maternal obesity has been associated with both gestational diabetes mellitus (GDM) and neonatal macrosomia. Most studies of obesity in pregnancy have demonstrated an increased risk for GDM. However, the contribution of obesity as an added risk in GDM has not been examined. The purpose of this study was to examine the contribution of obesity as a risk factor to perinatal morbidity in gestationally diabetic women by comparing the maternal and neonatal outcome in obese and nonobese gestationally diabetic women. From 1979 to 1983, the maternal, intrapartum, and neonatal characteristics of all prepartum gravid patients with GDM were examined. Of the 158 patients with documented GDM, 62 (39%) were obese (weight greater than 90 kg). There was no difference in maternal age (obese 29.3 +/- 5.4 years, nonobese 28.7 +/- 6.5 years) parity, or prepartum risk score between the obese and nonobese patients. The incidence of prematurity, pre-eclampsia, fetal distress, and primary cesarean sections were not different between the groups. There were no differences in Apgar scores, gestational age, or perinatal morbidity. However, the obese patients delivered heavier neonates expressed as mean birthweight (obese 3667 +/- 682 gms, nonobese 3331 +/- 750 gms. P less than .01), the number of macrosomic (greater than 4 kg) neonates (obese 37%, nonobese 14%, P less than .001) and K-score, (obese 0.8 +/- 1, nonobese 0.4 +/- 9, P less than .05). These data indicate that obese patients with GDM have an increased risk of neonatal macrosomia.(ABSTRACT TRUNCATED AT 250 WORDS)
Adult↗
Carbachol modulates GIP-mediated insulin release from rat pancreatic lobules in vitro.
Rat pancreatic lobules were used to investigate the interaction of gastric inhibitory polypeptide (GIP), carbachol, glucose, and an amino acid mixture on insulin secretion. At 5 mM glucose, GIP (1.1 ng/ml) did not augment insulin secretion in the presence or absence of carbachol (5 X 10(-5)M) during a 210-min incubation. However, at 11 mM glucose, GIP did augment insulin secretion in the presence (342.5 +/- 62.0 vs. 212.5 +/- 50.5 microU . ml-1 . mg tissue-1, mean +/- SE; P less than 0.01) but not the absence (217.0 +/- 45.5 vs. 205.8 +/- 35.0 microU . ml-1 . mg tissue-1) of carbachol. During subsequent 30-min incubations, GIP was increased to a supra-physiological concentration of 11 ng/ml and again augmented insulin secretion with (65.8 +/- 10.8 vs. 27.8 +/- 2.4 microU . ml-1 . mg tissue-1 . h-1; P less than 0.001) but not without (37.2 +/- 1.8 vs. 30.2 +/- 2 microU . ml-1 . mg-1 tissue-1 . h-1) carbachol present. This GIP-mediated insulin secretion was blocked by atropine (34.8 to 1.8 vs. 37.6 +/- 1.6 microU . ml-1 . mg tissue-1 . h-1). At amino acid concentrations of 21 and 211 mM, but not 2.1 mM, GIP augmented insulin release but again only with carbachol present. In conclusion, porcine GIP augments amino acid as well as glucose-mediated insulin secretion in vitro. Furthermore, this biological action is dependent on an, as yet, unidentified cholinergic mechanism. The pathophysiological significance of the neural-hormonal interaction deserves further investigation.
Amino Acids↗
Alanine production by the human fetus at term gestation.
In a previous study, we demonstrated the complete dependence of the human fetus on the mother for its glucose needs. As alanine is considered the major glucogenic amino acid synthesized endogenously and an important source of urea nitrogen, in the present study we examined whether the human fetus at term gestation can produce alanine. 5 normal pregnant women, undergoing elective cesarean section, were given a constant infusion of [2,3-13C2]alanine in trace quantities for a period of 4 h prior to and during surgery. Isotopic steady state was achieved in the maternal blood by 1.5 h and maintained through anesthesia and surgery. The 13C enrichment (mol% excess) of alanine was measured in the peripheral blood of the mother and in the simultaneously obtained umbilical arterial and venous blood at delivery. Even though the umbilical venous and arterial concentrations of alanine were similar, a 42% decrease in 13C enrichment of alanine occurred between umbilical vein and artery, 1.00 +/- 0.23 and 0.58 +/- 0.15%, respectively (mean +/- SD). These data suggest that the human fetus at term gestation following an overnight maternal fast produces alanine endogenously. This may serve to transfer nitrogen from fetal muscle to the liver for urea synthesis.
Alanine↗
Gestational diabetes mellitus. Is further improvement necessary?
The maternal antepartum, intrapartum, and neonatal characteristics of 158 patients with gestational diabetes mellitus (GDM) attending a large teaching hospital between 1979 and 1983 were described and compared with a matched nondiabetic control group. The primary cesarean section rate in patients with GDM (18%) was significantly greater than in the control group (11%, P less than 0.04). Neonatal macrosomia, as reflected in mean birthweight (P less than 0.04), the number of neonates weighing greater than 4 kg (P less than 0.05) and large-for-gestational-age infants (P less than 0.05), and the birthweight adjusted for gestational age (K-score, P less than 0.01) was significantly increased in the diabetic group. The characteristics of patients with GDM treated with diet alone and diet and insulin together were examined. The insulin-therapy group was characterized by more patients older than 25 yr (P less than 0.01) and a higher mean birthweight (3743 +/- 677 g) (P less than 0.02) than the diet-alone group. This may reflect an increased magnitude of glucose intolerance in the insulin-treated group. Obese patients with GDM delivered heavier neonates than the nonobese patients with GDM (P less than 0.01). Although there was no difference between the groups, perinatal mortality was present in this study. These data indicate that the major perinatal morbidity in GDM included increased cesarean section for fetal macrosomia. Early diagnosis with strict diagnostic criteria and rigid antenatal surveillance may result in further improvements in outcome.
Birth Weight↗
Management of third-trimester diabetic pregnancies with the use of continuous subcutaneous insulin infusion therapy: a pilot study.
Six women with juvenile-onset diabetes were managed as outpatients during the third trimester of pregnancy with continuous subcutaneous insulin infusion therapy. Twenty-four-hour metabolic profiles for plasma glucose, beta-hydroxybutyrate, and triglycerides were monitored prior to, 1 week, 5 weeks, and 10 weeks after initiation of continuous subcutaneous insulin infusion therapy and compared with the metabolic profiles of 10 normal (nondiabetic) pregnant women. Near-normal metabolic profiles were achieved in these patients after 5 weeks of therapy in this pilot study. Patient motivation, compliance, and understanding of their illness were crucial in achieving the therapeutic goals of normoglycemia.
3-Hydroxybutyric Acid↗
Determination of carbon-13 labeled lactate in blood by gas chromatography/mass spectrometry.
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Carbon Isotopes↗
Glucose turnover in chronic uremia: increased recycling with diminished oxidation of glucose.
The effects of chronic renal failure and hemodialysis on the glucose turnover rate, glucose carbon recycling, and glucose oxidation were evaluated in eight chronically uremic subjects. Six normal subjects served as controls. The studies were repeated in seven uremic subjects after they had been established on hemodialysis for 3 to 18 months. Glucose 13C(microliters) was administered by a prime-constant-rate infusion, and the isotopic enrichment of the whole glucose molecule (m + 6), ie, all six carbon atoms of glucose labeled with 13C and that of the C1 atom of glucose in the plasma were measured by mass spectrometry. It was assumed that the C1 atom of the glucose molecule represented the 13C enrichment of the individual glucose carbons. The "true" rate of glucose production was estimated from the dilution of the glucose 13C (microliters) mass (m + 6) in the plasma. In contrast to the whole glucose molecule (m + 6), recycling of tracer carbon resulted in an increased 13C enrichment of the C1 atom of the glucose molecule and an underestimation of glucose turnover ("apparent"). Glucose carbon recycling was estimated from the difference between the "true" and "apparent" rates of glucose turnover. The contribution of glucose to respiratory CO2 was quantified by comparing the 13C enrichment of expired CO2 with that of the plasma glucose carbon. The plasma glucose concentration after an overnight fast was similar in the uremic and control subjects (72.3 +/- 9.5 and 79.0 +/- 9.5 mg/dL, respectively; mean +/- SD).2+ while the "true" rates of glucose production were similar in both groups (normal: 2.02 +/- 0.19 mg/kg X min; uremic: 2.19 +/- 0.53 mg/kg X min).(ABSTRACT TRUNCATED AT 250 WORDS)
3-Hydroxybutyric Acid↗
Calculation of substrate turnover rate in stable isotope tracer studies.
The determination of substrate turnover rate with stable isotope-labeled compounds has advantages of being safe and applicable in the study of children and pregnant women. Currently, a majority of these studies has been performed with primed constant-rate infusion technique. The isotope enrichment of the substrate in the plasma is measured by gas chromatography-mass spectrometry (GCMS). The turnover rate is then calculated from steady-state kinetics. A number of different equations have been used by various investigators for this purpose. Based on theoretical consideration and experimental data, it is concluded that the equation P = [(1/E) - 1] I or P = (y/x) I should be used for a correct turnover rate calculation, where P is turnover rate in mumol X kg-1, E the isotope enrichment, I the infusion rate in mumol X kg-1 X min-1, and y/x the mole ratio of tracee to tracers. A GCMS standard curve constructed from isotope enrichment versus isotope peak abundance should be used for the former equation, whereas a standard curve constructed from mole ratio (x/y) versus isotope ratio should be used for the latter equation. Interchange of standard curves or use of other equations will produce erroneous turnover rate. This is especially significant when a low enriched isotope-labeled compound is used as a tracer.
Blood Glucose↗
Estimation of glucose carbon recycling and glucose turnover with [U-13C] glucose.
To estimate "true" rate of glucose production, as well as glucose carbon recycling in humans, a mass spectrometric method with [U-13C]glucose as tracer was developed. Because the opportunity for the uniformly labeled glucose, [13C6]glucose, to recycle back as [13C6]glucose is negligible, the true glucose production rate was obtained by measuring the plasma isotope enrichment of [13C6]glucose with chemical ionization mass spectrometry. In contrast, when the isotopic enrichment of C-1 of glucose was measured by enzymatic decarboxylation and ratio mass spectrometry, the "apparent" glucose production including carbon recycling was obtained. The difference between the two rates was the extent of glucose carbon recycling. [U-13C]glucose was administered as primed constant-rate infusion to six normal healthy adult subjects. Rates of glucose turnover were calculated from tracer dilution by applying steady-state kinetics. The true rate of glucose production estimated by the present method was 2.02 +/- 0.19 mg X kg-1 X min-1 (mean +/- SD). After an overnight fast, glucose carbon recycling contributed from 3 to 26% of the total glucose production rate. Use of stable isotopes and mass spectrometric technique permits estimation of important parameters of glucose metabolism without resorting to multiple tracers and at the same time preventing the risk of radiation.
Blood Glucose↗