Edward Kiwanuka

Visceral obesity is characterized by impaired nitric oxide-independent vasodilation

BACKGROUND Endothelial dysfunction has been described in obesity. This study examines the impact of visceral obesity on nitric oxide-independent relaxation in the human forearm. METHODS AND RESULTS In ten viscerally obese and ten matched controls forearm blood flow (FBF) was measured by venous occlusion plethysmography during intrabrachial infusion of: (1) sodium nitroprusside; (2) bradykinin, before and after inhibition of vasoactive prostaglandins and nitric oxide; (3) potassium; (4) ouabain (Na(+)/K(+)ATPase inhibitor) alone or (5) in combination with BaCl(2)(K(IR)inhibitor). Baseline FBF and endothelium-independent vasodilatation were similar in the two groups. In obese patients, bradykinin-induced increase of FBF was significantly less than in controls (P<0.01). Irrespective of prostaglandins and nitric oxide inhibition, bradykinin response was lower in the viscerally obese. Intrabrachial potassium determined a significantly blunted response (P<0.05). Ouabain caused a similar, moderate decrease in basal FBF in the two groups; the coinfusion of BaCl(2)caused a more intense decline in FBF which was significantly relevant in obese (-24+/-5%, P<0.01). CONCLUSIONS In obese patients there is a blunted nitric oxide-independent relaxation determined by a decreased response of inwardly rectifying potassium channels.

Slow versus fast proteins in the stimulation of beta-cell response and the activation of the entero-insular axis in type 2 diabetes.

We tested whether ingestion of whey protein can induce greater post‐prandial amino acid (AA) levels in the plasma and a higher beta‐cell response than casein ingestion in type 2 diabetes mellitus patients.

Evidence for Acute Stimulation of Fibrinogen Production by Glucagon in Humans

Fibrinogen, an acute-phase protein, and glucagon, a stress hormone, are often elevated in many conditions of physical and metabolic stress, including uncontrolled diabetes. However, the possible mechanisms for this association are poorly known. We have studied the acute effects of selective hyperglucagonemia (raised from ∼200 to ∼350 pg/ml for 3 h) on fibrinogen fractional secretion rate (FSR) in eight normal subjects during infusion of somatostatin and replacement doses of insulin, glucagon, and growth hormone. Fibrinogen FSR was evaluated by precursor-product relationships using either Phe (n = 8) or Leu (n = 2) tracers. Hyperglucagonemia did not change either plasma Phe or Tyr specific activity. After hyperglucagonemia, fibrinogen FSR increased by ∼65% (from 12.9 ± 3.6 to 21.5 ± 6.1% per day, P < 0.025) using plasma Phe specific activity as the precursor pool. FSR increased by ∼80% (from 16.6 ± 4.8 to 29.4 ± 8.8% per day, P < 0.025) if plasma Phe specific activity was corrected for the ketoisocaproate/Leu enrichment (or specific activity) ratio to obtain an approximate estimate of intrahepatic Phe specific activity. FSR increased by ∼60% when using plasma Tyr specific activity as precursor pool (n = 8) (P < 0.05), as well as when using the Leu tracer precursorproduct relationship (n = 2). In conclusion, selective hyperglucagonemia for ∼3 h acutely stimulated fibrinogen FSR using a Phe tracer method. Thus, glucagon may be involved in the increase of fibrinogen concentration and FSR observed under stressed or pathologic conditions.

The role of substrates in the regulation of protein metabolism

Substrates are powerful modulators of amino acid and protein turnover in vivo (Table 4). Intravenous infusions of amino acids exert a protein-anabolic effect, because they directly inhibit endogenous protein degradation and stimulate protein synthesis at the whole-body level. A stimulation of protein synthesis has been observed also at the forearm level. These changes resulted in an improvement of body and tissue protein balance, which is the ultimate goal of any nutritional intervention aimed at preserving body protein stores. In humans acute intravenous infusions of carbohydrates do not appear to affect either protein degradation or leucine oxidation. However, animal studies support the view that glucose availability spares essential amino acids at least in the fetus. The effects of hypercaloric refeeding with high-carbohydrate diets may, however, result in increased protein turnover. Lipids, in the form of long-chain fatty acids, inhibit endogenous protein breakdown and may suppress leucine oxidation in the whole body. They do not affect protein synthesis. In contrast, medium-chain fatty acids apparently increased leucine oxidation, and therefore increased net protein catabolism. Ketone bodies may be anabolic provided that fatty acid concentrations are not concurrently decreased.

Hyperglucagonemia stimulates phenylalanine oxidation in humans

Glucagon stimulates in vitro liver phenylalanine (Phe) degradation, thus inducing net protein catabolism. Whether these effects occur also in vivo in humans is not known. Therefore, we studied the effects of physiological hyperglucagonemia on Phe rate of appearance (Rα), hydroxylation, and oxidation in seven normal volunteers during infusions of somatostatin with replacement doses of insulin and growth hormone. Steady-state Phe kinetics were evaluated using the l-[1-14C]Phe tracer both at the end of a 3-h basal glucagon replacement period (glucagon concentration: 212 ± 115 ng/l) and after a 3-h hormone infusion at the rate of ∼ 3 ng · kg−1 · min−1 (→654 ± 280 ng/l). Hyperglucagonemia did not change plasma Phe concentration and Ra but increased Phe oxidation by ∼ 30% (P < 0.01). Oxidation was also increased by ∼ 24% (P < 0.01) using plasma [14C]tyrosine (Tyr) specific activity as a precursor pool. Phe hydroxylation to Tyr estimated by assuming a fixed ratio of Tyr to Phe Rα (0.73) did not change. Nonhydroxylated Phe disposal decreased by ∼ 6% (P = 0.08). These data show that in humans in the postabsorptive state, hyperglucagonemia, with near maintenance of basal insulin and growth hormone concentrations, stimulates Phe oxidation but not Phe hydroxylation, suggesting a different regulation of these two Phe catabolic steps. Glucagon may also reduce Phe availability for protein synthesis.

Elevated non-esterified fatty acids impair nitric oxide independent vasodilation, in humans: evidence for a role of inwardly rectifying potassium channels

UNLABELLED To evaluate the role of elevation of non-esterified fatty acids on forearm nitric oxide (NO) dependent and independent relaxation, four studies were performed in the forearms of 14 normals: (1). endothelium-dependent and -independent vasodilations were assessed during acetylcholine (Ach) and sodium nitroprusside (SNP) infusions; (2). flow-mediated vasodilation (FMD) was assessed; (3) .bradykinin (BK) was infused during NO and prostaglandin inhibition (NO clamp); (4). blood flow (FBF) was measured during Ouabain, a Na(+)/K(+) ATPase, and BaCl(2), rectifying potassium channel (K(IR)) blockers, respectively. All studies were performed before and after 120 min. Intralipid+heparin (high-NEFA) infusion. Ach-mediated FBF increase was lower at high-NEFA (332+/-34 vs. 436+/-44% at 45 microg l forearm(-1) min(-1); % of ratio infused: control arm P<0.05), while SNP response was similar. FMD did not differ before and during high-NEFA, which induced a blunted response of FBF during BK with or without NO clamp. Ouabain and BaCl(2)-mediated FBF inhibition was lower (P<0.01) at high-NEFA. During ouabain alone FBF decreased slightly. IN CONCLUSION High-NEFA exerts a negative role on both NO-dependent and independent vasodilations. The decrease in FBF, mediated by K(IR) inhibition, is blunted by high-NEFA: these substrates interfere with hemodynamic/metabolism coupling, possibly through the inhibition of these channels.

Insulin infusion normalizes fasting and post‐prandial albumin and fibrinogen synthesis in Type 1 diabetes mellitus

Aims  The effect of metabolic control on hepatic synthesis of plasma proteins in Type 1 diabetes mellitus (T1DM), in the post‐absorptive and post‐prandial state, is not known.

Fibrinogen kinetics and protein turnover in obese non-diabetic males: Effects of insulin

Although hyperfibrinogenemia and insulin resistance are common in obesity and diabetes mellitus, the impact of obesity per se on fibrinogen turnover and the insulin effects on fibrinogen and protein kinetics is unknown.

Nonesterified fatty acids and endothelial dysfunction

Nonesterified fatty acids (NEFA) induce vascular effects, such as the inhibition of insulin-induced nitric oxide (NO) production. In small arteries, relaxation is largely NO-independent. We aimed to assess the effect of elevated NEFA on NO-independent vasodilation. Protocols were performed before and after 120 min of a lipid emulsion infusion. We performed: (1) the flow-induced dilatation of the brachial artery (NO-dependent), (2) intrabrachial bradykinin (BK) infusion before and after inhibition of prostaglandins (PG) and NO and (3) intraarterial infusion of ouabain, a Na+/K+ ATPase blocker, alone or in combination with BaCl2, a potassium channel blocker. No changes in flow-mediated vasodilation were induced by elevated NEFA. After the inhibition of PG and NO, BK increased forearm blood flow (FBF) similarly, indicating that the increase in FBF is not dependent on NO and PG production. However, elevated NEFA blunt FBF on both occasions. Coinfusion of ouabain with BaCl2 caused a significant decline in FBF in baseline condition (−48±5%, p<0.01). This effect on FBF was blunted at high NEFA (−28±2%, p<0.01 vs. baseline condition). In conclusion, elevated NEFA do not impair NO-dependent vasodilation; this effect appears to be mediated by a reduced potassium-mediated vasodilation. This makes more likely their negative action on metabolism and haemodynamic coupling.

Decreased Homocysteine Trans-Sulfuration in Hypertension With Hyperhomocysteinemia: Relationship With Insulin Resistance

Context Homocysteine is an independent cardiovascular risk factor and is elevated in essential hypertension. Insulin stimulates homocysteine catabolism in healthy individuals. However, the mechanisms of hyperhomocysteinemia and its relationship with insulin resistance in essential hypertension are unknown. Objective To investigate whole body methionine and homocysteine kinetics and the effects of insulin in essential hypertension. Design and Setting Eight hypertensive male subjects and six male normotensive controls were infused with l-[methyl-2H3,1-13C]methionine for 6 hours. In the last 3 hours a euglycemic, hyperinsulinemic clamp was performed. Steady-state methionine and homocysteine kinetics were determined in postabsorptive and hyperinsulinemic conditions. Results Postabsorptive hypertensive subjects had elevated homocysteine concentrations (+30%, P = 0.035) and slightly (by 15% to 20%) but insignificantly lower methionine rates of appearance (Ras) (P = 0.07 to P = 0.05) and utilization for protein synthesis (P = 0.06) than postabsorptive normotensive controls. Hyperinsulinemia suppressed methionine Ra and protein synthesis, whereas it increased homocysteine trans-sulfuration, clearance, and methionine transmethylation (the latter only in the normotensive subjects). However, in the hypertensive subjects trans-sulfuration was significantly lower (P < 0.05) and increased ~50% less [by +1.59 ± 0.34 vs +3.45 ± 0.52 µmol/kg lean body mass (LBM) per hour, P < 0.005] than in normotensive controls. Homocysteine clearance through trans-sulfuration was ~50% lower in hypertensive than in normotensive subjects (P < 0.005). In the hypertensive subjects, insulin-mediated glucose disposal was ~45% lower (460 ± 44 vs 792 ± 67 mg/kg LBM per hour, P < 0.0005) than in normotensive controls and was positively correlated with the increase of trans-sulfuration (P < 0.0015). Conclusions In subjects with essential hypertension, hyperhomocysteinemia is associated with decreased homocysteine trans-sulfuration and probably represents a feature of insulin resistance.