Insulin entry into muscle involves a saturable process in the vascular endothelium.

AIMS/HYPOTHESIS: Insulin's rate of entry into skeletal muscle appears to be the rate-limiting step for muscle insulin action and is slowed by insulin resistance. Despite its obvious importance, uncertainty remains as to whether the transport of insulin from plasma to muscle interstitium is a passive diffusional process or a saturable transport process regulated by the insulin receptor. METHODS: To address this, here we directly measured the rate of (125)I-labelled insulin uptake by rat hindlimb muscle and examined how that is affected by adding unlabelled insulin at high concentrations. We used mono-iodinated [(125)I]Tyr(A14)-labelled insulin and short (5 min) exposure times, combined with trichloroacetic acid precipitation, to trace intact bioactive insulin. RESULTS: Compared with saline, high concentrations of unlabelled insulin delivered either continuously (insulin clamp) or as a single bolus, significantly raised plasma (125)I-labelled insulin, slowed the movement of (125)I-labelled insulin from plasma into liver, spleen and heart (p < 0.05, for each) but increased kidney (125)I-labelled insulin uptake. High concentrations of unlabelled insulin delivered either continuously (insulin clamp), or as a single bolus, significantly decreased skeletal muscle (125)I-labelled insulin clearance (p < 0.01 for each). Increasing muscle perfusion by electrical stimulation did not prevent the inhibitory effect of unlabelled insulin on muscle (125)I-labelled insulin clearance. CONCLUSIONS/INTERPRETATION: These results indicate that insulin's trans-endothelial movement within muscle is a saturable process, which is likely to involve the insulin receptor. Current findings, together with other recent reports, suggest that trans-endothelial insulin transport may be an important site at which muscle insulin action is modulated in clinical and pathological settings.

Muscle microvascular recruitment predicts insulin sensitivity in middle-aged patients with type 1 diabetes mellitus.

AIMS/HYPOTHESIS: Insulin delivery to muscle is rate-limiting for insulin's metabolic action and is regulated by insulin's own action to increase skeletal muscle blood flow and to recruit microvasculature. Microvascular dysfunction has been observed in insulin resistant states. We investigated the relation between insulin's action to recruit microvasculature and its metabolic action in type 1 diabetes. METHODS: Near euglycaemia was obtained by an overnight insulin infusion during 17 inpatient admissions of participants with type 1 diabetes. This was followed by a 2 h 1 mU kg⁻¹ min⁻¹ euglycaemic-hyperinsulinaemic clamp. Microvascular blood volume (MBV) was assessed using contrast-enhanced ultrasound 10 min before and 30 min after starting the clamp. RESULTS: We observed that, after overnight modest hyperinsulinaemia (average ≈ 286 pmol/l), MBV was positively related to the steady-state insulin sensitivity measured during the subsequent clamp (r = 0.62, p = 0.008). The more marked hyperinsulinaemia during the clamp (average steady-state insulin ≈ 900 pmol/l) increased MBV in the more insulin resistant participants within 30 min but not in the insulin sensitive participants. The change in MBV during the clamp was negatively correlated to the insulin sensitivity (r = -0.55, p = 0.022). As a result, MBV after 30 min of marked hyperinsulinaemia was comparable between the insulin sensitive and resistant participants. CONCLUSIONS/INTERPRETATION: We conclude that moderate overnight hyperinsulinaemia recruited microvasculature in the more sensitive participants, while higher levels of plasma insulin were needed for more insulin resistant participants. This suggests that microvascular responsiveness to insulin is one determinant of metabolic insulin sensitivity in type 1 diabetes.

The vascular actions of insulin control its delivery to muscle and regulate the rate-limiting step in skeletal muscle insulin action.

Evidence suggests that insulin delivery to skeletal muscle interstitium is the rate-limiting step in insulin-stimulated muscle glucose uptake and that this process is impaired by insulin resistance. In this review we examine the basis for the hypothesis that insulin acts on the vasculature at three discrete steps to enhance its own delivery to muscle: (1) relaxation of resistance vessels to increase total blood flow; (2) relaxation of pre-capillary arterioles to increase the microvascular exchange surface perfused within skeletal muscle (microvascular recruitment); and (3) the trans-endothelial transport (TET) of insulin. Insulin can relax resistance vessels and increase blood flow to skeletal muscle. However, there is controversy as to whether this occurs at physiological concentrations of, and exposure times to, insulin. The microvasculature is recruited more quickly and at lower insulin concentrations than are needed to increase total blood flow, a finding consistent with a physiological role for insulin in muscle insulin delivery. Microvascular recruitment is impaired by obesity, diabetes and nitric oxide synthase inhibitors. Insulin TET is a third potential site for regulating insulin delivery. This is underscored by the consistent finding that steady-state insulin concentrations in plasma are approximately twice those in muscle interstitium. Recent in vivo and in vitro findings suggest that insulin traverses the vascular endothelium via a trans-cellular, receptor-mediated pathway, and emerging data indicate that insulin acts on the endothelium to facilitate its own TET. Thus, muscle insulin delivery, which is rate-limiting for its metabolic action, is itself regulated by insulin at multiple steps. These findings highlight the need to further understand the role of the vascular actions of insulin in metabolic regulation.

Serological changes observed in horses infected with Anoplocephala perfoliata after treatment with praziquantel and natural reinfection.

The serological changes in two groups of horses known to be harbouring Anoplocephala perfoliata were studied; 12 were treated with 1.5 mg/kg praziquantel and 200 microg/kg ivermectin, and 14 were treated with 200 microg/kg ivermectin. Serological and faecal analyses were carried out on each animal at intervals for 758 days. The titres of antibodies specific for A perfoliata decreased from the day of treatment to day 28 in both groups, and continued to decrease in the group treated with praziquantel and ivermectin, with the first significant decrease from the other group at day 121. From day 151 to day 295 the first significant increase in antibody levels in the group treated with both drugs was observed; no A perfoliata eggs were detected in the faeces of these animals until day 295 when five of the 10 were positive.

Endothelial Na+-D-glucose cotransporter: no role in insulin-mediated glucose uptake.

A recent report indicates that the Na+-D-glucose cotransporter SGLT1 is present in capillaries of skeletal muscle and is required for insulin-mediated glucose uptake in myocytes. This result is based on the complete inhibition of insulin-mediated muscle glucose uptake by phlorizin, an inhibitor of SGLT1. Using the pump-perfused rat hind limb, we measured glucose uptake, lactate efflux, and radioactive 2-deoxyglucose uptake into individual muscles with saline (control), phlorizin, insulin, and insulin plus phlorizin, as well as with saline and insulin using normal and low Na+ perfusion buffer. Insulin-mediated glucose uptake was not inhibited after correction for phlorizin interference in the glucose assay. Lactate efflux and 2-deoxyglucose uptake by individual muscles were unaffected by phlorizin. Low Na+ buffer did not affect insulin-mediated glucose uptake, lactate efflux, or 2-deoxyglucose uptake. We conclude that endothelial SGLT1 exerts no barrier for glucose delivery to myocytes.

Field trial of the efficacy of a combination of ivermectin and praziquantel in horses infected with roundworms and tapeworms.

Two hundred and thirty-three horses were screened for the presence of roundworms by faecal egg counts (FECs) and for tapeworms by an ELISA specific for antibodies to the immunodominant 12 kDa and 13 kDa tapeworms antigen. The 62 horses were found to be infected with both parasites were treated with a combination of 0.2 mg/kg ivermectin and 1.5 mg/kg praziquantel. The treatment suppressed the median FEC of the horses to zero for 10 weeks and significantly reduced their anti-12/13 kDa antibody levels. The estimated risk of tapeworm-associated colic in these horses was halved by 12 weeks after the treatment.

Inhibiting NOS blocks microvascular recruitment and blunts muscle glucose uptake in response to insulin.

We examined the effects of inhibiting nitric oxide synthase with Nomega-nitro-l-arginine-methyl ester (l-NAME) on total hindlimb blood flow, muscle microvascular recruitment, and hindlimb glucose uptake during euglycemic hyperinsulinemia in vivo in the rat. We used two independent methods to measure microvascular perfusion. In one group of animals, microvascular recruitment was measured using the metabolism of exogenously infused 1-methylxanthine (1-MX), and in a second group contrast-enhanced ultrasound (CEU) was used. Limb glucose uptake was measured by arterial-venous concentration differences after 2 h of insulin infusion. Saline alone did not alter femoral artery flow, glucose uptake, or 1-MX metabolism. Insulin (10 mU.min-1.kg-1) significantly increased hindlimb total blood flow (0.69 +/- 0.02 to 1.22 +/- 0.11 ml/min, P < 0.05), glucose uptake (0.27 +/- 0.05 to 0.95 +/- 0.08 micromol/min, P < 0.05), 1-MX uptake (5.0 +/- 0.5 to 8.5 +/- 1.0 nmol/min, P < 0.05), and skeletal muscle microvascular volume measured by CEU (10.0 +/- 1.6 to 15.0 +/- 1.2 video intensity units, P < 0.05). Addition of l-NAME to insulin completely blocked the effect of insulin on both total limb flow and microvascular recruitment (measured using either 1-MX or CEU) and blunted glucose uptake by 40% (P < 0.05). We conclude that insulin specifically recruits flow to the microvasculture in skeletal muscle via a nitric oxide-dependent pathway and that this may be important to insulin's overall action to regulate glucose disposal.

Skeletal muscle microvascular recruitment by physiological hyperinsulinemia precedes increases in total blood flow.

Supraphysiological doses of insulin enhance total limb blood flow and recruit capillaries in skeletal muscle. Whether these processes change in response to physiological hyperinsulinemia is uncertain. To examine this, we infused either saline (n = 6) or insulin (euglycemic clamp, 3.0 mU x min(-1) x kg(-1), n = 9) into anesthetized rats for 120 min. Femoral artery flow was monitored continuously using a Doppler flow probe, and muscle microvascular recruitment was assessed by metabolism of infused 1-methylxanthine (1-MX) and by contrast-enhanced ultrasound (CEU). Insulin infusion raised plasma insulin concentrations by approximately 10-fold. Compared with saline, physiological hyperinsulinemia increased femoral artery flow (1.02 +/- 0.10 vs. 0.68 +/- 0.09 ml/min; P < 0.05), microvascular recruitment (measured by 1-MX metabolism [6.6 +/- 0.5 vs. 4.5 +/- 0.48 nmol/min; P < 0.05] as well as by CEU [167.0 +/- 39.8 vs. 28.2 +/- 13.8%; P < 0.01]), and microvascular flow velocity (beta, 0.14 +/- 0.02 vs. 0.09 +/- 0.02 s(-1)). Subsequently, we studied the time dependency of insulin's vascular action in a second group (n = 5) of animals. Using CEU, microvascular volume was measured at 0, 30, and 90 min of insulin infusion. Insulin augmented microvascular perfusion within 30 min (52.8 +/- 14.8%), and this persisted at 90 min (64.6 +/- 9.9%). Microvascular recruitment occurred without changes to femoral artery flow or beta. We conclude that insulin increases tissue perfusion by recruiting microvascular beds, and at physiological concentrations this precedes increases in total muscle blood flow by 60-90 min.

Evolving structures in surgical oncology and the role of the Federation of European Cancer Societies in continuing medical education.

This article describes the evolution of a European system of accreditation of educational events in oncology and the establishment by the Federation of European Cancer Societies of the Accreditation Council of Oncology in Europe. It draws attention to the need for a coordinated system which is acceptable in the different European countries so that an international system of "Eurocredits" can be devised. Through the official Union Europeénne des Médecins Specialistes (UEMS), reciprocity with the accrediting bodies in the United States and other countries is planned.

Branched chain amino acids activate messenger ribonucleic acid translation regulatory proteins in human skeletal muscle, and glucocorticoids blunt this action.

Branched chain amino acids (BCAA) are particularly effective anabolic agents. Recent in vitro studies suggest that amino acids, particularly leucine, activate a signaling pathway that enhances messenger ribonucleic acid translation and protein synthesis. The physiological relevance of these findings to normal human physiology is uncertain. We examined the effects of BCAA on the phosphorylation of eukaryotic initiation factor 4E-binding protein 1 (eIF4E-BP1) and ribosomal protein S6 kinase (p70(S6K)) in skeletal muscle of seven healthy volunteers. We simultaneously examined whether BCAA affect urinary nitrogen excretion and forearm skeletal muscle protein turnover and whether the catabolic action of glucocorticoids could be mediated in part by inhibition of the action of BCAA on the protein synthetic apparatus. BCAA infusion decreased urinary nitrogen excretion (P < 0.02), whole body phenylalanine flux (P < 0.02), plasma phenylalanine concentration (P < 0.001), and improved forearm phenylalanine balance (P = 0.03). BCAA also increased the phosphorylation of both eIF4E-BP1 (P < 0.02) and p70(S6K) (P < 0.03), consistent with an action to activate the protein synthetic apparatus. Dexamethasone increased plasma phenylalanine concentration (P < 0.001), prevented the BCAA-induced anabolic shift in forearm protein balance, and inhibited their action on the phosphorylation of p70(S6K). We conclude that in human skeletal muscle BCAA act directly as nutrient signals to activate messenger ribonucleic acid translation and potentiate protein synthesis. Glucocorticoids interfere with this action, and that may be part of the mechanism by which they promote net protein catabolism in muscle.

Pre-replantation storage of avulsed teeth: fact and fiction.

Recent laboratory and clinical studies have proven that there is a rapid decrease in the regenerative potential of normal periodontal ligament the longer an avulsed tooth is out of the socket. These findings make some guidelines for the management of avulsed teeth inaccurate. This paper will review the effects of pre-replantation storage on periodontal ligament healing. In addition, current management recommendations are reviewed and suggestions for change presented.

Dexamethasone inhibits the stimulation of muscle protein synthesis and PHAS-I and p70 S6-kinase phosphorylation.

Glucocorticoids inhibit protein synthesis in muscle. In contrast, insulin and amino acids exert anabolic actions that arise in part from their ability to phosphorylate ribosomal p70 S6-kinase (p70(S6k)) and eukaryotic initiation factor (eIF)4E binding protein (BP)1 (PHAS-I), proteins that regulate translation initiation. Whether glucocorticoids interfere with this action was examined by giving rats either dexamethasone (DEX, 300 microg. kg(-1). day(-1), n = 10) or saline (n = 10) for 5 days. We then measured the phosphorylation of PHAS-I and p70(S6k) in rectus muscle biopsies taken before and at the end of a 180-min infusion of either insulin (10 mU. min(-1). kg(-1) euglycemic insulin clamp, n = 5 for both DEX- and saline-treated groups) or a balanced amino acid mixture (n = 5 for each group also). Protein synthesis was also measured during the infusion period. The results were that DEX-treated rats had higher fasting insulin, slower glucose disposal, less lean body mass, and decreased protein synthetic rates during insulin or amino acid infusion (P < 0.05 each). DEX did not affect basal PHAS-I or p70(S6k) phosphorylation but blocked insulin-stimulated phosphorylation of PHAS-I- and amino acid-stimulated phosphorylation of both PHAS-I and p70(S6k) (P < 0.01, for each). DEX also increased muscle PHAS-I concentration. These effects can, in part, explain glucocorticoid-induced muscle wasting.

Heterogeneity of laser Doppler flowmetry in perfused muscle indicative of nutritive and nonnutritive flow.

Laser Doppler flowmetry (LDF) signal responses have been compared with metabolic changes using both a surface macroprobe and randomly placed implantable microprobes in muscles of the constant-flow-perfused rat hindlimb. Changes in response to total flow and to vasoconstrictors that are known to increase (norepinephrine, NE) or decrease (serotonin, 5-HT) hindlimb oxygen uptake were assessed. The surface macroprobe (anterior end of biceps femoris) identified only one type of LDF response characterized by increased signal in response to NE and decreased signal in response to 5-HT. Implanted microprobes (tibialis, gastrocnemius, vastus, or bicep femoris) identified sites that gave three LDF responses of differing character. These responses were where the LDF signal increased with NE and decreased with 5-HT (56.7%), where the LDF signal decreased with NE and increased with 5-HT (16.5%), or where there was no net response to either vasoconstrictor (24.7%). The data are consistent with discrete regions of nutritive and nonnutritive flow in muscle where flow in each as controlled by vasoconstrictors relates directly to the metabolic behavior of the tissue.

Insulin stimulates laser Doppler signal by rat muscle in vivo, consistent with nutritive flow recruitment.

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 x min(-1) x kg(-1)), adrenaline (0.125 microg.min(-1) x kg(-1)) or saline. By 1 h, insulin had increased the glucose infusion rate from 0 to 128 micromol.min(-1) x 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.