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The effect of infusions of recombinant insulin-like growth factor-I (IGF-I) (34, 103 or 688 pmol min-1 kg-1), insulin (3.4, 10.3 or 68.8 pmol min-1 kg-1) or combined infusions (34 pmol IGF-I + 3.4 pmol min-1 kg-1 insulin or 103 pmol IGF-I + 3.4 pmol min-1 kg-1 insulin) on protein metabolism, using an infusion of [1-14C]leucine was investigated in anaesthetized fasted dogs. Leucine concentration, production rate (measure of protein degradation), oxidation rate and non-oxidative disappearance rate (measure of protein synthesis) were decreased in a similar dose dependent manner by the IGF-I and insulin infusions (P < 0.01). The decrease in these measurements of leucine metabolism were greater following 34 pmol IGF-I + 3.4 pmol insulin than with either component infused alone (P < 0.05). Free fatty acid concentrations were decreased by all insulin doses (P < 0.01) but only by 103 and 688 pmol min-1 kg-1 insulin-like growth factor (P < 0.05, P < 0.01). These data demonstrate that IGF-I, like insulin, has a dose dependent effect on protein metabolism and that combined insulin and IGF-I infusions have additive effects on protein metabolism.

Objective: Results from studies on the effect of glucocorticosteroids on protein turnover in both rat and man have been conflicting. The aim of this study was to investigate the primary cause of muscle wasting in patients with Cushing's syndrome., Design: Studies of whole body 1(-14)C-leucine turnover in patients with Cushing's syndrome before and after successful treatment, and in control subjects., Patients: Eleven patients with Cushing's syndrome before and after (n = 5) treatment and 11 control subjects., Measurements: Whole body 1(-14)C-leucine turnover to determine leucine metabolic clearance rate, leucine production rate, leucine oxidation rate and leucine incorporation into protein., Results: Plasma leucine concentration (mean +/- SEM 100 +/- 6 mumol/l), leucine metabolic clearance rate (9.97 +/- 0.11 mumol/min/kg), leucine turnover (0.98 +/- 0.11 mumol/min/kg) and leucine incorporation into protein (0.71 +/- 0.09 mumol/min/kg) were all significantly reduced in patients with Cushing's syndrome compared with control subjects (122 +/- 6 mumol/l, P < 0.05; 13.61 +/- 1.27 mumol/min/kg, P < 0.05; 1.65 +/- 0.12 mumol/min/kg, P < 0.05; 1.46 +/- 0.10 mumol/min/kg, P < 0.001, respectively). Leucine oxidation rate was similar in the patients with Cushing's syndrome and control subjects. When leucine metabolism was expressed in terms of lean body mass (LBM) in five patients with Cushing's syndrome and 11 control subjects, leucine MCR, leucine turnover and leucine oxidation were not significantly different in the two groups. However, leucine incorporation into protein was significantly reduced (P < 0.001) in the patients with Cushing's syndrome (1.07 +/- 0.20 mumol/min/kg LBM) compared with control subjects (1.95 +/- 0.11 mumol/min/kg LBM)., Conclusion: We conclude from these studies that the muscle wasting associated with Cushing's syndrome is primarily due to a reduction in protein synthesis.

The effects of growth hormone (GH) treatment on protein metabolism were studied in adults with GH deficiency (GHD). A double-blind, placebo-controlled trial of recombinant human GH, 0.018 IU/kg/day for 1 month followed by 0.036 IU/kg/day for 1 month, was performed with isotopic whole-body protein turnover studies at 0 and 2 months. In all, 18 adults with GHD (9 men, 9 women; mean age, 46.6 years; range, 30-56 years) were studied. Whole-body isotopic leucine turnover using L-[1-13C]leucine was assessed by measuring leucine Ra (a measure of protein degradation), non-oxidative leucine Rd (a measure of protein synthesis) and leucine oxidation rate. Lean body mass and circulating insulin-like growth factor I were significantly (p < 0.02) increased at 2 months in the GH-treated group, but not in the placebo group. There was no change in leucine Ra in either the placebo or GH-treated groups at 2 months. Leucine oxidation decreased (p < 0.01) and non-oxidative leucine Rd increased (p < 0.02) in the GH-treated group at 2 months. There was no significant change in either leucine oxidation or non-oxidative leucine Rd in the placebo group at 2 months. These results indicate that the increase in lean body mass resulting from GH treatment in adults with GHD is due to an increase in protein synthesis.

To investigate the effect of gender on catecholamine responses to hypoglycaemia, single-step euglycaemic-hypoglycaemic clamps have been performed in 14 healthy men and 17 women. Adrenaline responses were 44% lower in females (p < 0.01) and noradrenaline 17% lower (p = 0.08). In response to low-dose intravenous insulin infusion (0.3 mU.kg-1.min-1), plasma glucose fall and counterregulation in seven men and seven women had a different course (p < 0.001), with different glucose kinetics. In men, endogenous glucose output recovered quickly to levels that exceeded basal; in women suppression of endogenous glucose output was more prolonged, without rates ever exceeding basal (p < 0.05). Peripheral glucose uptake was stimulated in men only. The hormones of acute glucose counterregulation (catecholamines and glucagon) did not differ between the sexes during this challenge, the catecholamine response in the women being supported by the continuous fall in plasma glucose. These results suggest that: 1) catecholamine responses to moderately controlled hypoglycaemia are diminished in women, and 2) peripheral insulin sensitivity in men is enhanced over that of women but hepatic sensitivity to insulin may be greater in women.

Objective: Growth hormone treatment given to adult growth hormone deficient patients leads to an increase in lean body mass by an unknown mechanism. The aim of this study was to investigate the actions of growth hormone treatment on protein metabolism in adult growth hormone deficient patients., Design: Double-blind, placebo controlled trial of recombinant human growth hormone (0.018 U/kg/day for 1 month followed by 0.036 U/kg/day for 1 month) with isotopic whole body protein turnover studies at 0 and 2 months., Patients: Eighteen adult growth hormone deficient patients (nine male, nine female of mean age 46.6 (range 30-56)., Measurements: Whole body isotopic leucine turnover using L-1-13C-leucine measuring leucine Ra (a measure of protein degradation), non-oxidative leucine Rd (a measure of protein synthesis) and leucine oxidation rate., Results: Lean body mass (P < 0.02), circulating insulin-like growth factor I (P < 0.01) and insulin (P < 0.02) were significantly increased at 2 months in the treatment group but there was no change in the placebo group. When expressed in relation to body weight, leucine Ra and non-oxidative leucine Rd increased (P < 0.01) and leucine oxidation decreased (P < 0.02) after 2 months growth hormone treatment. When expressed in relation to lean body mass non-oxidative leucine Rd increased (P < 0.02) and leucine oxidation decreased (P < 0.02) but there was no significant change in leucine Ra after 2 months growth hormone treatment. In the placebo group there were no significant changes in leucine metabolism expressed as lean body mass or body weight after 2 months. changes in leucine metabolism expressed as lean body mass or body weight after 2 months., Conclusion: These results indicate that the increase in lean body mass resulting from growth hormone treatment in adult growth hormone deficient patients is due to an increase in protein synthesis.

Glucose intolerance, sometimes severe enough to cause frank diabetes mellitus, is a frequent feature of Cushing's syndrome. The primary cause of the hyperglycaemia, whether due to glucose over-production or under-utilization, remains unresolved. We therefore measured glucose turnover using an intravenous bolus of 3-3H glucose in 14 normoglycaemic patients with Cushing's syndrome and 14 control subjects. Seven of the patients with Cushing's syndrome were also restudied post-operatively. Plasma glucose concentrations were similar in all three groups whereas glucose metabolic clearance rate (MCR) (1.80 +/- 0.06 ml/min/kg) and glucose turnover rate (9.09 +/- 0.36 mumol/min/kg) were significantly reduced in patients with Cushing's syndrome compared to normal subjects (2.21 +/- 0.1; P less than 0.001; 10.90 +/- 0.50; P less than 0.01) and rose post-operatively to normal values (2.35 +/- 0.14 ml/min/kg; 11.07 +/- 0.48 mumol/min/kg). We conclude from these results that the hyperglycaemia sometimes found in Cushing's syndrome may be primarily due to decreased utilization rather than increased glucose production.

Glucose and leucine metabolism were investigated in 5 poorly controlled non-insulin-dependent diabetics (NIDDM) following an i.v. injection of 3-[3H]glucose and 1-[14C]leucine in the morning and evening. In the morning glucose concentration (11.2 +/- 0.8 mmol/l) (mean +/- SEM) and production rate (14.2 +/- 1.3 mumol/min/kg) were significantly greater (P less than 0.001, P less than 0.05) and glucose metabolic clearance rate (MCR) (1.3 +/- 0.2 ml/min/kg) significantly lower (P less than 0.05) than in a group of control subjects. Glucose concentration was lower in the evening (P less than 0.05) as a result of a decrease in glucose production rate (P less than 0.05). Leucine concentration and production rate were not significantly different from normal but leucine oxidation rate was increased (P less than 0.05). There was no diurnal variation in leucine metabolism. Since leucine production is a measure of protein breakdown, the higher morning glucose production rate was not due to an increased supply of gluconeogenic precursors from protein catabolism.

1. The effect of an infusion of sodium beta-hydroxybutyrate on leucine and alanine metabolism was investigated in dogs starved for 12 h. To determine whether the metabolic changes produced by this infusion were due to the resultant alkalaemia the effect of an equimolar infusion of sodium bicarbonate was also studied. 2. The sodium beta-hydroxybutyrate infusion reduced alanine concentration as a result of a decrease in alanine production rate and an increase in alanine metabolic clearance rate. The sodium bicarbonate infusion induced a small decrease in alanine concentration which was due to an increased metabolic clearance rate. Alanine production rate showed no change. This demonstrates that the fall in alanine concentration after a sodium beta-hydroxybutyrate infusion is due both to a ketone-specific inhibitory effect on alanine production rate and an increased metabolic clearance rate caused by the alkalaemia. 3. Leucine concentration was increased after the ketone infusion due to a small increase in production rate and there was a small increase in the rate of leucine incorporation into protein. Alkalaemia had no effect on leucine concentration or metabolism.

The rate of turnover of glucose or leucine can be measured in the steady state by using the radioactive isotopes 14C or 3H to 'trace' these metabolites. The tracer can either be injected or infused intravenously and its metabolism followed by monitoring levels of the tracer in blood, breath and urine. If a 14C labelled metabolite is used the oxidation rate may sometimes be determined by measuring the expiry rate of 14CO2. If the single injection technique is used the specific activity curve is fitted with an exponential function and the area under the curve calculated. Turnover rate is calculated from dose of isotope injected/area under the specific activity time curve. This technique can be used to construct a compartmental model to describe the behaviour of the metabolite. If the constant infusion technique is used, tracer is infused until a steady state level of tracer is achieved. This plateau is used to calculate the turnover of the metabolite from infusion rate of tracer/specific activity at steady state. While this latter method provides the simplest method of calculating turnover it cannot be used to model the data. The infusion technique can be used to measure changes in turnover and oxidation in the non-steady state. Tracer is infused to a steady state level and the system is then perturbed by for example, the infusion of a hormone. The changes in Ra and Rd can be determined either by using the Steele equation which assumes a single pool or by using compartmental analysis.

A patient with acid maltase deficiency was treated with a high protein diet for 7 months. Protein turnover expressed in terms of lean body mass was shown to be increased in this patient before the diet but was markedly reduced following the diet. The patient improved clinically whilst on the diet both subjectively and in terms of mobility, breathing and reduced peripheral cyanosis at rest.

Leucine production rate, metabolic clearance rate and oxidation rate were measured in 10 Type 1 (insulin-dependent) diabetic patients after 24 h insulin withdrawal, conventional insulin therapy and an overnight insulin infusion to maintain normoglycaemia, and in 10 control subjects. In the insulin-withdrawn patients, leucine concentration (259 +/- 17 mumol/l), production rate (2.65 +/- 0.29 mumol . min-1 . kg-1) and oxidation rate (0.69 +/- 0.10 mumol . min-1 . kg-1) were significantly greater (p less than 0.001; p less than 0.05; p less than 0.005 respectively) than corresponding values in control subjects (127 +/- 6; 1.81 +/- 0.12; 0.19 +/- 0.02). Following conventional insulin therapy, leucine concentration (162 +/- 12 mumol/l) and oxidation rate (0.43 +/- 0.05 mumol . min-1 . kg-1) were lower than after insulin withdrawal but were still significantly greater than in control subjects (p less than 0.05; p less than 0.005). Although leucine concentration, production rate and metabolic clearance rate were normal after an overnight insulin infusion, leucine oxidation rate was still greater than normal (0.34 +/- 0.06 mumol . min-1 . kg-1; p less than 0.05). These results suggest that increased leucine concentration in insulin deficiency is due to elevated leucine production rate caused by increased proteolysis, and that leucine concentration is restored to normal by insulin treatment.

Turnover rates of glucose, free fatty acids (FFA) and leucine have been measured in newly diagnosed, uncontrolled insulin-dependent diabetic (IDD) patients. The results have been compared with data collected from the same patients while on conventional insulin therapy as well as after overnight intravenous infusion of insulin with sustained normoglycaemia. The data have been analysed by compartmental and non-compartmental methods and the results have been compared with simultaneously collected data on respiratory exchange. Oxidation rates of 14C-labelled substrates have also been measured. Tracer studies were done on established diabetics after insulin withdrawal and subsequent intravenous infusion of insulin at different rates. The results confirm the in vivo importance of the glucose-fatty acid cycle, indicating that when glucose, FFA and ketone bodies are available in excess it is FFA and ketones that are metabolized in preference to glucose. The data emphasize the importance of increased production rates rather than decreased utilization rates in producing high concentrations of substrates in the plasma of insulin-deficient patients.

Leucine turnover was measured using [1-14C] L-leucine in three patients with classical maple syrup urine disease. There was measurable leucine oxidation although it was lower than in normal adults. Leucine production rate was greater than normal in all three patients with an increased rate of incorporation of leucine into protein and increased protein catabolism. These fluxes were both relatively insensitive to exogenous insulin.

Leucine and alanine production rate was measured in 5 patients with acid maltase deficiency in the postabsorptive state, following 6 months on a normal diet with placebo and 6 months on an isocaloric high protein diet (16-22% protein). Whole body leucine production rate, a measure of protein degradation, expressed in terms of lean body mass was significantly greater than in five control subjects. Following the high protein diet, leucine production rate was decreased in four of the five patients but this was not statistically significant. Alanine production rate expressed in terms of lean body mass was significantly greater than in control subjects. After the high protein diet, alanine production rate and concentration were significantly decreased (p less than 0.05). There were no significant improvements in any of the clinically relevant variables measured in these patients. It is possible that a larger increase in protein intake over a longer time period may have a clinical effect.

1. The biosynthesis of cholesterol in vivo was studied at a number of tissue sites in rats by using 3H2O as precursor. Overall, the mass of cholesterol synthesized was in good agreement with the rate of cholesterogenesis, as determined by kinetic analysis of cholesterol specific-radioactivity-time curves after administration of radiolabelled cholesterol. 2. Dietary cholesterol increased the circulating concentration of cholesterol and inhibited endogenous cholesterogenesis, with concomitant increases in the concentration of esterified cholesterol, in all tissues studied. Addition of ororic acid to the cholesterol-supplemented diet tended to reverse each of these changes in extrahepatic tissues. 3. The co-ordinated change in cholesterol biosynthesis and esterification, with no change in total cholesterol content, in extrahepatic tissues, is attributed to control by receptor-mediated lipoprotein uptake. 4. Further reduction of the concentration of the apoprotein B-containing lipoproteins by addition of orotic acid to a diet without supplementary cholesterol did not further enhance cholesterogenesis. We consider that the relatively high rates of extrahepatic cholesterogenesis in normolipidaemic rats are attributable to the low concentration of low-density lipoprotein.