Endothelial dysfunction and vascular insulin resistance usually coexist and chronic inflammation engenders both. In the present study, we investigate the temporal relationship between vascular insulin resistance and metabolic insulin resistance. We assessed insulin responses in all arterial segments, including aorta, distal saphenous artery and the microvasculature, as well as the metabolic insulin responses in muscle in rats fed on a high-fat diet (HFD) for various durations ranging from 3 days to 4 weeks with or without sodium salicylate treatment. Compared with controls, HFD feeding significantly blunted insulin-mediated Akt (protein kinase B) and eNOS [endothelial nitric oxide (NO) synthase] phosphorylation in aorta in 1 week, blunted vasodilatory response in small resistance vessel in 4 weeks and microvascular recruitment in as early as 3 days. Insulin-stimulated whole body glucose disposal did not begin to progressively decrease until after 1 week. Salicylate treatment fully inhibited vascular inflammation, prevented microvascular insulin resistance and significantly improved muscle metabolic responses to insulin. We conclude that microvascular insulin resistance is an early event in diet-induced obesity and insulin resistance and inflammation plays an essential role in this process. Our data suggest microvascular insulin resistance contributes to the development of metabolic insulin resistance in muscle and muscle microvasculature is a potential therapeutic target in the prevention and treatment of diabetes and its related complications.

Insulin increases capillary recruitment in vivo and impairment of this may contribute to muscle insulin resistance by limiting either insulin or glucose delivery. In the present study, the effect of progressively decreased rat muscle perfusion on insulin action using graded occlusion with MS (microspheres; 15 μm in diameter) was examined. EC (energy charge), PCr/Cr (phosphocreatine/creatine ratio), AMPK (AMP-activated protein kinase) phosphorylation on Thr 172 (P-AMPKα/total AMPK), oxygen uptake, nutritive capacity, 2-deoxyglucose uptake, Akt phosphorylation on Ser 473 (P-Akt/total Akt) and muscle 2-deoxyglucose uptake were determined. Arterial injection of MS (0, 9, 15 and 30×10 6 MS/15 g of hindlimb muscle, as a bolus) into the pump-perfused (0.5 ml·min −1 ·g −1 of wet weight) rat hindlimb led to increased pressure (−0.5±0.8, 15.9±2.1, 28.7±4.6 and 60.3±9.4 mmHg respectively) with minimal changes in oxygen uptake. Nutritive capacity was decreased from 10.6±1.0 to 3.8±0.9 μmol·g −1 of muscle·h −1 ( P <0.05) with 30×10 6 MS. EC was unchanged, but PCr/Cr was decreased dose-dependently to 61% of basal with 30×10 6 MS. Insulin-mediated increases in P-Akt/total Akt decreased from 2.15±0.35 to 1.41±0.23 ( P <0.05) and muscle 2-deoxyglucose uptake decreased from 130±19 to 80±12 μg·min −1 ·g −1 of dry weight ( P <0.05) with 15×10 6 MS; basal P-AMPKα in the absence of insulin was increased, but basal P-Akt/total Akt and muscle 2-deoxyglucose uptake were unaffected. In conclusion, partial occlusion of the hindlimb muscle has no effect on basal glucose uptake and marginally impacts on oxygen uptake, but markedly impairs insulin delivery to muscle and, thus, insulin-mediated Akt phosphorylation and glucose uptake.

Insulin-mediated increases in limb blood flow are thought to enhance glucose uptake by skeletal muscle. Using the perfused rat hindlimb, we report that macro laser Doppler flowmetry (LDF) probes positioned on the surface of muscle detect changes in muscle capillary (nutritive) flow. With this as background, we examined the effects of insulin and adrenaline (epinephrine), which are both known to increase total leg blood flow, on the LDF signals from scanning and stationary probes on the muscle surface in vivo . The aim is to assess the relationship between capillary recruitment, total limb blood flow and glucose metabolism. Glucose infusion rate, femoral arterial blood flow (FBF) and muscle LDF, using either scanning or a stationary probe positioned over the biceps femoris muscle, were measured. With scanning LDF, animals received insulin (10 m-units·min -1 ·kg -1 ), adrenaline (0.125 µ g·min -1 ·kg -1 ) or saline. By 1 h, insulin had increased the glucose infusion rate from 0 to 128 µ mol·min -1 ·kg -1 and the scanning LDF had increased by 62±8% ( P < 0.05), but FBF was unaffected. Adrenaline increased FBF by 49% at 15 min, but LDF was unchanged. With saline at 1 h, neither FBF nor LDF had changed. With the stationary LDF surface probe, insulin at 1 h had increased FBF by 47% ( P < 0.05) and LDF by 47% ( P < 0.05) relative to saline controls. Adrenaline increased FBF (39%), but LDF was unaltered. The stimulation of LDF by insulin is consistent with capillary recruitment (nutritive flow) as part of the action of this hormone in vivo . The recruitment may be independent of changes in total flow, as adrenaline, which also increased FBF, did not increase LDF. The time of onset suggests that LDF closely parallels glucose uptake. Thus, depending on probe design, measurement of muscle haemodynamic effects mediated by insulin in normally responsive and insulin-resistant patients should be possible.

1. Using the forearm balance method, together with systemic infusions of l-[ ring -2,6- 3 H]phenylalanine and l-[1- 14 C]leucine, we examined the effects of infused branched-chain amino acids on whole-body and skeletal muscle amino acid kinetics in 10 postabsorptive normal subjects; 10 control subjects received only saline. 2. Infusion of branched-chain amino acids caused a four-fold rise in arterial branched-chain amino acid levels and a two-fold rise in branched-chain keto acids; significant declines were observed in circulating levels of most other amino acids, including phenylalanine, which fell by 34%. Plasma insulin levels were unchanged from basal levels (8 ± 1 μ-units/ml). 3. Whole-body phenylalanine flux, an index of proteolysis, was significantly suppressed by branched-chain amino acid infusion ( P < 0.002), and forearm phenylalanine production was also inhibited ( P < 0.03). With branched-chain amino acid infusion total leucine flux rose, with marked increments in both oxidative and non-oxidative leucine disposal ( P < 0.001). Proteolysis, as measured by endogenous leucine production, showed a modest 12% decrease, although this was not significant when compared with saline controls. The net forearm balance of leucine and other branched-chain amino acids changed from a basal net output to a marked net uptake ( P < 0.001) during branched-chain amino acid infusion, with significant stimulation of local leucine disposal. Despite the rise in whole-body non-oxidative leucine disposal, and in forearm leucine uptake and disposal, forearm phenylalanine disposal, an index of muscle protein synthesis, was not stimulated by infusion of branched-chain amino acids. 4. The results suggest that in normal man branched-chain amino acid infusion suppresses skeletal muscle proteolysis independently of any rise of plasma insulin. Muscle branched-chain amino acid uptake rose dramatically in the absence of any apparent increase in muscle protein synthesis, as measured by phenylalanine disposal, or in branched-chain keto acid release. Thus, an increase in muscle branched-chain amino acid concentrations and/ or local branched-chain amino acid oxidation must account for the increased disposal of branched-chain amino acids.

1. Studies were conducted to test the hypothesis that glycerol-induced acute renal failure in rats may be mediated by 5-hydroxytryptamine. 2. The tryptophan hydroxylase inhibitor, β-chlorophenylalanine, or saline was administered for 4 days before performance of 24 h clearance studies after glycerol administration. 3. p -Chlorophenylalanine significantly reduced the nephrotoxic effect of glycerol, as evidenced by improved glomerular filtration rate, urine volume excretion and absolute sodium excretion, and reduced plasma creatinine concentration. 4. These results suggest that glycerol-induced acute renal failure may be mediated by the renovascular and/or tubular actions of 5-hydroxytryptamine.

1. In rats, intra-arterial metoclopramide, a dopamine antagonist, resulted in an elevation of plasma aldosterone at 5 min and plasma renin activity at 10 min and peak aldosterone and renin responses at 10 and 30 min respectively. 2. Pre-administration of l-dopa blunted and delayed aldosterone and renin responses to metoclopramide, indicating that metoclopramide-induced plasma aldosterone and plasma renin activity increments are mediated by a direct effect of blockade of dopamine receptors rather than other effects of this drug. 3. Pre-administration of angiotensin converting enzyme inhibitor, captopril (SQ 14 225) and the angiotensin II antagonist, saralasin, as well as bilateral nephrectomy did not significantly affect the aldosterone response to metoclopramide, Thus dopaminergic modulation of aldosterone secretion occurs independently of alterations in the renin-angiotensin system. 4. Modulating effects of dopamine on plasma aldosterone are probably mediated by direct effects as well as by interaction with other factors influencing aldosterone secretion at the adrenal zona glomerulosa.

1. Human polymorphonuclear leucocyte elastase and cathepsin G were incubated with preparations of isolated human glomerular basement membrane at neutral pH and 37°C. 2. The ability of these enzymes to degrade glomerular basement membrane was followed by the release of hydroxyproline. Both proteinases released considerable amounts of hydroxyproline. 3. By using Sephadex G-100 it was shown that the solubilized basement membrane fragments appeared as a single peak and had a molecular weight of over 100 000. These proteins after reduction were analysed by sodium dodecyl sulphate-gel electrophoresis to examine their subunit pattern and determine their molecular size. 4. The released basement membrane proteins gave at least four precipitin lines with a rabbit anti-(glomerular basement membrane) antiserum. 5. These results support the concept that polymorphonuclear leucocyte neutral proteinases play an important role in the pathogenesis of glomerulonephritis. 6. At acid pH values cathepsin B also released hydroxyproline from human glomerular basement membrane but the lysosomal carboxyl proteinase, cathepsin D, had no action.

1. Prostaglandin E 2 significantly inhibits the renin reaction in whole plasma as well as in the isolated system of semi-purified human renin and human renin substrate. The inhibitory effect of prostaglandin A 2 was less marked in whole plasma and absent in the isolated system. 2. The inhibitory effect of prostaglandin E 2 was more marked in normal than hypertensive plasma and was maximal at the lowest concentration used. In hypertensive plasma the maximal inhibitory effect was achieved at tenfold higher concentrations. 3. In normal plasma prostaglandin E 2 does not affect the rate of product formation ( k 5 = k 6 ), but inhibits the overall renin reaction by decreasing the total amount of available enzyme-substrate and enzyme-substrate modifier complex ( K 2 K 3 ). 4. In hypertensive plasma prostaglandin E 2 acts as a potential accelerator of the rate of product formation ( k 6 k 5 ). In the range of substrate concentration employed, the apparent inhibitory effect is explained by an even greater lack of available complex ( K 2 K 3 ). This behaviour in hypertensive plasma is consistent with the presence of an additional modifier (? activator).