Biomedical subjects

S L Nissen

Publications and source records attributed to S L Nissen.

10 recordsLinked to original sources

PubMed1992

Gas chromatographic/mass spectrometric analysis of stable isotopes of 3-methylhistidine in biological fluids: application to plasma kinetics in vivo.

A simple and rapid method for measuring 3-methylhistidine (3MH) in plasma and urine is described. Internal standard, 1-methylhistidine (1MH), was added to plasma, acidified and absorbed onto cation-exchange columns. It was then eluted from columns, dried, and derivatized for gas chromatography/mass spectrometry. A major fragment of 3MH was monitored at 238 u and 3-methyl-(methyl-2H3)histidine (d3-3MH) (used for in vivo kinetics) at 241 u, whereas 1MH was monitored at 340 u and eluted 0.5 min later than 3MH. Standard curves for plasma analysis were linear and nanamole amounts of 3MH in plasma were determined with a precision of 3.5%. 3MH was also quantitated in urine; however, because of substantial amounts of 1MH, (18O2)1MH was used as the internal standard. Nanamole amounts of 3MH were determined in urine with a precision of 2.7%. Application of the 3MH analytical method was used to develop a kinetic compartmental model by using the stable isotope of 3MH, d3-3MH. Cattle, like humans, quantitatively excrete 3MH in the urine. A young bovine was injected with d3-3MH and the enrichment curve in plasma was evaluated in order to obtain a steady-state production rate of 3MH. The decay curve was modeled through the use of NIH-SAAM modeling program. The kinetics of d3-3MH from plasma were adequately described by a three-pool compartmental model. The de novo production rate of 3MH estimated in the calf was 665 mumol per day. This corresponded to an estimated fractional turnover rate of 1.56% per day, which was similar to estimates obtained from urine collections.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1992

Technical note: the use of a compartmental model to estimate the de novo production rate of N tau-methylhistidine in cattle.

Urinary N tau-methylhistidine (NMH) excretion has been used as an index of muscle protein breakdown in cattle. An alternative means to estimate muscle proteolysis in cattle is to estimate the de novo production of NMH from plasma kinetics isotopically. Three crossbred steers (average 229 kg) were given a 5.0-mg bolus intravenous injection of [methyl-2H3-N tau-methylhistidine (d3-NMH), after which 16 serial blood samples and three consecutive 24-h urine samples were taken. The enrichment of NMH in plasma was determined by gas chromatography-mass spectrometry, and compartmental analysis of the kinetic data was performed using the SAAM modeling program. The NMH production rates per day (NMHPR, micromoles per day) were 732, 782, and 725, and the fractional breakdown rates (FBR, percentage per day) were 1.61, 1.72, and 1.58 as determined by urinary excretion of NMH, by a three-pool catenary model (plasma kinetics, Model A), and by a more descriptive, three-pool model with two response curves (both plasma and urine kinetics, Model B), respectively. Model A and B estimates of NMHPR and FBR were similar (P greater than .25) to those of estimates obtained from urinary NMH excretion. Kinetic modeling also allows calculation of compartment mass and flux of NMH between compartments and indicates that when NMH exists the muscle pool it is rapidly excreted via the urine. In conclusion, kinetic modeling offers an alternative approach to estimating the NMH production rate.

Animals↗

PubMed1991

Leucine and its catabolites alter mitogen-stimulated DNA synthesis by bovine lymphocytes.

This study determined effects of leucine and its catabolites on in vitro, mitogen-stimulated DNA synthesis by bovine lymphocytes. Cultures grown in leucine-free or leucine-replete (0.4 mmol/L leucine) medium were supplemented with 0-10.0 mmol/L leucine or individual catabolites. Leucine at greater than or equal to 0.08 mmol/L was necessary for normal DNA synthesis by mitogen-stimulated bovine lymphocytes. beta-Hydroxy-beta-methylbutyrate (HMB) and beta-hydroxy-beta-methylglutarate (HMG) had minimal effect on unresponsiveness of mitogen-stimulated bovine lymphocytes in leucine-free medium; however, alpha-ketoisocaproate (KIC) at 0.4 and 2.0 mmol/L partially or completely restored DNA synthesis. In leucine-replete medium, 0.016-0.4 mmol/L KIC and 0.016-2.0 mmol/L HMB and HMG did not affect DNA synthesis. At 2.0 and 10.0 mmol/L, KIC inhibited (P less than 0.01) DNA synthesis, whereas HMB and HMG at 10.0 mmol/L enhanced (P less than 0.01) DNA synthesis. Overall, these results suggest that leucine is necessary for mitogen-induced DNA synthesis by bovine lymphocytes, and that this requirement for leucine can be partially met by KIC. When leucine was not limiting, KIC, HMB and HMG at concentrations that might occur in vivo did not alter lymphocyte DNA synthesis in vitro.

Adult↗

PubMed1988

Regulation of whole-body leucine metabolism with insulin during mixed-meal absorption in normal and diabetic humans.

To determine the effects of insulin on dietary and endogenous leucine metabolism, five normal subjects, seven insulin-insufficient insulin-dependent (IDDM) diabetic patients, and five diabetic patients controlled with continuous subcutaneous insulin infusion (CSII) were studied before and for 8 h after ingestion of a chemically defined elemental test meal (10 cal/kg) containing crystalline amino acids. L-[1-14C]leucine was included in the meal to trace the entry and oxidation of the dietary leucine. Total (meal + endogenous) entry of leucine into the circulation was estimated with a constant infusion of [2H3]leucine. Postabsorptive and meal-related increases in the plasma leucine concentration were greater (P less than .05) in the insulin-insufficient IDDM than in the normal subjects but returned to near-normal values with CSII. Baseline leucine flux was approximately 40% greater in the insulin-insufficient IDDM than in normal subjects (2.17 +/- 0.17 vs. 1.55 +/- 0.15 mumol.kg-1.min-1, respectively; .05 less than P less than .01) but were near normal during CSII treatment (1.85 +/- 0.25 mumol.kg-1.min-1). Furthermore, total leucine entry during meal absorption was greater in the insulin-insufficient IDDM (1.41 +/- 0.10 mmol.kg-1.8 h-1) than in either normal (0.96 +/- 0.08 mmol.kg-1.8 h-1, P less than .01) or IDDM subjects during CSII treatment (1.09 +/- 0.11 mmol.kg-1.8 h-1, P less than .05). Fractional oxidation (approximately 40-50%) and entry of dietary leucine were similar in all three groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1986

Inverse relationship of leucine flux and oxidation to free fatty acid availability in vivo.

To determine the effect of fatty acid availability on leucine metabolism, 14-h fasted dogs were infused with either glycerol or triglyceride plus heparin, and 46-h fasted dogs were infused with either nicotinic acid or nicotinic acid plus triglyceride and heparin. Leucine metabolism was assessed using a simultaneous infusion of L-[4,5-3H]leucine and alpha-[1-14C]ketoisocaproate. Leucine, alpha-ketoisocaproate (KIC), and totalleucine carbon (leucine plus KIC) flux and oxidation rates were calculated at steady state. In 14-h fasted animals, infusion of triglyceride and heparin increased plasma free fatty acids (FFA) by 0.7 mM (P less than 0.01) and decreased leucine (P less than 0.01), total leucine carbon flux (P less than 0.02), and oxidation (P less than 0.05). The estimated rate of leucine utilization not accounted for by oxidation and KIC flux decreased, but the changes were not significant. During glycerol infusion, leucine and KIC flux and oxidation did not change. In 46-h fasted dogs, nicotinic acid decreased FFA by 1.0 mM (P less than 0.01) and increased (P less than 0.05) the rate of leucine and total leucine carbon flux, but did not affect KIC flux. Leucine oxidation increased (P less than 0.01) by nearly threefold, whereas nonoxidized leucine utilization decreased. Infusion of triglyceride plus heparin together with nicotinic acid blunted some of the responses observed with nicotinic acid alone. In that changes in oxidation under steady state condition reflect changes in net leucine balance, these data suggest that FFA availability may positively affect the sparing of at least one essential amino acid and may influence whole body protein metabolism.

Animals↗

PubMed1985

Effects of [15N]leucine infused at low rates on leucine metabolism in humans.

The present studies were carried out to determine whether infusions of [15N]leucine at low rates affect estimates of leucine oxidation and of proteolysis and protein synthesis in humans. Three groups of normal subjects were infused for 3 h with either [15N]leucine at a rate of 0.16 or 0.26 mumol X kg-1 X min-1 or saline using [2H3]leucine and alpha-[14C]ketoisocaproate as isotopic tracers of leucine metabolism. Data were analyzed at steady state using both single- and dual-isotope models. Preliminary studies were carried out to characterize the dual-isotope model in humans using infusions of [3H]leucine and alpha-[14C]ketoisocaproate. In the postabsorptive state estimates of leucine appearance, disappearance, and oxidation derived from the two isotope models were in good agreement. Infusion of stable isotope up to approximately 10% of the leucine carbon flux do not have a significant effect on leucine metabolism, but the data derived from such studies must be properly controlled and interpreted with care because these tracers are not massless.

Breath Tests↗

PubMed1984

Insulin binding on cultured chick muscle cells: decrease in binding associated with cell fusion.

Binding of 125I-bovine and chicken insulin to cultured embryonic chick skeletal muscle cells was studied. Bovine and chicken insulin bound cultured cells with high affinities of 2.4 X 10(9)M-1 and 4.8 X 10(9)M-1 and low affinities of 2.4 X 10(7)M-1 and 3.7 X 10(7)M-1, respectively. Maximum insulin binding was achieved after 90 min of incubation at 20 degrees C and the maximum value was maintained for an additional 3 hr. Insulin binding increased in a linear manner with increasing nuclei number over a 5-fold range. Maximum insulin binding per nuclei decreased as cell fusion increased between 24 and 72 hr in culture, primarily due to a decrease in the number of low affinity insulin receptors.

Animals↗

PubMed1984

Effects of epinephrine infusion on leucine and alanine kinetics in humans.

Infusion of epinephrine in humans increases glucose production and decreases plasma concentrations of some essential amino acids such as leucine, while not affecting the plasma concentration of the potential gluconeogenic amino acid alanine. To determine whether epinephrine alters alanine and leucine metabolism, rates of appearance (Ra) and disappearance (Rd) of glucose, alanine, and leucine were determined in postabsorptive volunteers using [3H]glucose, [2H3]alanine, [15N]leucine, and [2H3]leucine during a 180-min infusion of epinephrine (50 ng X kg-1 X min-1). Plasma glucose (90 +/- 1 to 142 +/- 5 mg/dl) and insulin (10 +/- 1 to 16 +/- 2 micrograms/ml) increased (P less than 0.05), whereas plasma alanine concentrations did not change and plasma leucine concentrations increased (127 +/- 5 to 72 +/- 3 microM). Glucose Ra increased transiently and returned to basal values by 120 min. In contrast, alanine Ra and Rd increased identically and progressively from 5.7 +/- 0.5 to 14.5 +/- 1.9 mumol X kg-1 X min-1 by 180 min. Although leucine nitrogen Ra increased transiently and returned to basal values, leucine carbon Ra and Rd decreased (P less than 0.05) during the infusion of epinephrine. The calculated rate and percent of leucine nitrogen going to alanine increased, whereas the percent of alanine nitrogen derived from leucine remained constant. The increase in alanine Ra was entirely attributable to increased de novo synthesis because proteolysis, as estimated by leucine carbon flux, decreased.

Adolescent↗

PubMed1983

Effects of free fatty acid availability, glucagon excess, and insulin deficiency on ketone body production in postabsorptive man.

The present studies were undertaken to assess the relative effects of free fatty acid (FFA) availability, glucagon excess, and insulin deficiency on ketone body (KB) production in man. To determine whether an increase in FFA availability would augment KB production in the absence of insulin deficiency and glucagon excess, plasma insulin and glucagon were maintained at basal concentrations by infusion of somatostatin and exogenous insulin and glucagon, and plasma FFA were increased from 0.32 +/- 0.06 to 1.4 +/- 0.1 mM by a 2.5-h-infusion of a triglyceride emulsion plus heparin. KB production increased fivefold from 2.2 +/- 0.4 to 11.4 +/- 1.2 mumol . kg-1 . min-1, P less than 0.001. To determine whether insulin deficiency would further augment KB production, analogous experiments were performed but the replacement infusion of insulin was stopped. Despite a greater increase in plasma FFA (from 0.26 +/- 0.04 to 1.95 +/- 0.3 mM), KB production increased (from 1.5 +/- 0.3 to 11.1 +/- 1.8 mumol . kg-1 . min-1) to the same extent as in the absence of insulin deficiency. To determine whether hyperglucagonemia would augment KB production beyond that accompanying an increase in plasma FFA and, if so, whether this required insulin deficiency, similar experiments were performed in which the glucagon infusion rate was increased to produce plasma glucagon concentrations of 450-550 pg/ml with and without maintenance of the basal insulin infusion. When basal plasma insulin concentrations were maintained, hyperglucagonemia did not further increase KB production; however, when the basal insulin infusion was discontinued, hyperglucagonemia increased KB production significantly, whereas no change was observed in saline control experiments. These studies indicate that, in man, FFA availability is a major determinant of rates of KB production; insulin does not appear to influence ketogenesis rates by a direct hepatic effect, and glucagon can further augment KB production when FFA concentrations are increased but only in the setting of insulin deficiency.

3-Hydroxybutyric Acid↗

PubMed1983

Failure of infused beta-hydroxybutyrate to decrease proteolysis in man.

Ketone bodies have been suggested to have a protein-sparing effect, since infusion of Na-beta-hydroxybutyrate in man decreases plasma alanine concentrations and urinary nitrogen (N) excretion. To test this hypothesis, six normal postabsorptive volunteers were infused with Na-beta-hydroxybutyrate for 3 h. Rates of glucose, leucine carbon, and alanine appearance and disappearance from the plasma space were traced with [3-3H]glucose, L-[6,6,6-2H3]leucine, and [2,3,3,3-2H4]alanine. Rates of leucine N appearance and disappearance and the rate of transfer of leucine N to alanine were assessed with [15N]leucine. During ketone body infusion, plasma alanine decreased (P less than 0.05), whereas plasma leucine increased (P less than 0.05). Rates of alanine appearance increased (5.3 +/- 0.3 to 7.8 +/- 0.6 mumol/kg X min), but the increase in its rate of disappearance was slightly greater, accounting for the decrease in plasma alanine concentration. Leucine N flux and the rate and percent of leucine N transferred to alanine increased, whereas leucine carbon flux was unchanged. To determine the effect of the alkalemia induced by Na-beta-hydroxybutyrate, four additional subjects were infused with NaHCO3. Alkalemia had no effect on leucine N or carbon flux or on the rate of appearance of alanine, but increased the rate of alanine disappearance, resulting in a decrease in the plasma alanine concentration. Since the rate of appearance of leucine carbon was unaltered during the infusion of Na-beta-hydroxybutyrate, it is unlikely that hyperketonemia per se decreases proteolysis in postabsorptive man.

3-Hydroxybutyric Acid↗