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Although many effects of both acute and chronic hypoxia on the circulation are well characterized, the distribution and regulation of blood flow (BF) heterogeneity in skeletal muscle during systemic hypoxia is not well understood in humans. We measured muscle BF within the thigh muscles of nine healthy young men using positron emission tomography during one-leg dynamic knee extension exercise in normoxia and moderate physiological systemic hypoxia (14% [O.sub.2] corresponding to ~3,400 m of altitude) without and with local adenosine receptor inhibition with femoral artery infusion of aminophylline. Systemic hypoxia reduced oxygen extraction of the limb but increased muscle BF, and this flow increment was confined solely to the exercising quadriceps femoris muscle. Exercising muscle BF heterogeneity was reduced from rest (P = 0.055) but was not affected by hypoxia. Adenosine receptor inhibition had no effect on capillary BF during exercise in either normoxia or hypoxia. Finally, one-leg exercise increased muscle BF heterogeneity both in the resting posterior hamstring part of the exercising leg and in the resting contralateral leg, whereas mean BF was unchanged. In conclusion, the results show that increased BF during one-leg exercise in moderate hypoxia is confined only to the contracting muscles, and the working muscle hyperemia appears not to be directly mediated by adenosine. Increased flow heterogeneity in noncontracting muscles likely reflects sympathetic nervous constraints to curtail BF increments in areas other than working skeletal muscles, but this effect is not potentiated in moderate systemic hypoxia during small muscle mass exercise. positron emission tomography; exercise; hypoxia doi: 10.1152/ajpregu.00056.2010.

Byline: Gregory M. T. Hare (1,2), Elaine Liu (1), Andrew J. Baker (1), C. David Mazer (1,2) Keywords: Hemoglobin based oxygen carrier; Hemodilution; Cerebral hypoxia; Lactate Abstract: Purpose To determine the oxygen affinity for optimal tissue oxygen delivery with a hemoglobin--hydroxyethyl starch conjugate (HRC 101). Methods Anesthetized rats were hemodiluted (180 ml kg.sup.-1) with low (P.sub.50 ~70 mmHg) or high affinity (P.sub.50 ~14 mmHg) HRC 101 at hemoglobin (Hb) concentrations near 100 or 70 g l.sup.-1 (n = 6--8). Hippocampal tissue oxygen tension ([P.sub.Br]O.sub.2), blood flow, arterial blood gases, Hb, hematocrit (Hct) and lactate were measured. Data (mean +- SD) were analyzed by two-way ANOVA. Results Hemodilution reduced the hematocrit to 1 +- 1% in all groups. [P.sub.Br]O.sub.2 was best maintained after hemodilution with low affinity HRC 101 at Hb 100 and 70 g l.sup.-1 (25.2 +- 7.6 and 16.6 +- 8.3 torr, respectively). [P.sub.Br]O.sub.2 decreased (9.5 +- 9.3 torr, P < 0.05) and serum lactate levels increased (5.0 +- 1.7 mmol l.sup.-1, P < 0.05) following hemodilution with the high affinity HRC 101 (Hb 100 g l.sup.-1). Conclusions HRC 101 with a lower oxygen affinity favored tissue perfusion and maintained [P.sub.Br]O.sub.2 after near complete blood volume exchange in rats. Author Affiliation: (1) Departments of Anesthesia and Critical Care, Cara Phelan Centre for Trauma Research, The Keenan Research Centre, Li Ka Shing Knowledge Institute, St. Michael's Hospital, University of Toronto, 30 Bond Street, Toronto, ON, M5B 1W8, Canada (2) Department of Physiology, University of Toronto, Toronto, ON, M5S 1A8, Canada Article History: Registration Date: 28/05/2009 Received Date: 29/12/2008 Accepted Date: 16/05/2009 Online Date: 10/07/2009 Article note: Preliminary results were presented at the meeting of 10th International Society of Blood Substitutes, Providence, Rhode Island, 13 June 2005. Dr. Hare is a recipient of the Bristol-Myers Squibb-CAS Career Scientist Award. Electronic supplementary material The online version of this article (doi: 10.1007/s00134-009-1532-2) contains supplementary material, which is available to authorized users.

Byline: Ryan C. Arnold (1), Joseph E. Parrillo (2), R. Phillip Dellinger (2), Michael E. Chansky (1), Nathan I. Shapiro (4), David J. Lundy (3), Stephen Trzeciak (1,2), Steven M. Hollenberg (2) Keywords: Microcirculation; Shock; Resuscitation; Perfusion; Critical care; Emergency medicine Abstract: Objective Sublingual microvascular videomicroscopy can assess tissue perfusion in critically ill patients however, data analysis is currently limited to delayed off-line evaluation. We hypothesized that a real-time point-of-care (POC) determination of the microcirculatory flow index (MFI), an established metric for assessing microcirculatory perfusion, agrees well with the conventional off-line analysis. Design Prospective observational study. Setting Urban academic intensive care unit. Participants A heterogeneous population of critically ill patients. Measurements and results A single operator performed side stream darkfield videomicroscopy of the sublingual microcirculation and made a POC determination of MFI in real-time on a portable bedside monitor by assigning a score (0 = no flow to 3 = normal) to each quadrant of the image and averaging the four values. After image processing, de-identification and randomization, the same operator, blinded to the previous interpretation, repeated the MFI assessment by viewing an AVI-formatted image sequence on a 94 cm 1,080 pixel LCD monitor (reference standard). There were 205 paired measurements in 18 subjects. The POC and reference standard MFI had good agreement by Bland--Altman analysis [mean difference of -0.031, SD = 0.198 (95% CI, -0.43 to 0.37)]. The POC assessment was 94% sensitive and 92% specific for detecting impaired microvascular flow (defined a priori as an MFI < 2.5 based on previously published data). Conclusions A POC determination of MFI had good agreement with conventional off-line analysis, and was highly sensitive and specific for detecting impaired microvascular flow. This real-time technique may be useful in future clinical trials targeting impaired microcirculatory perfusion in critically ill patients. Author Affiliation: (1) Department of Emergency Medicine, UMDNJ-Robert Wood Johnson Medical School at Camden, Cooper University Hospital, One Cooper Plaza, Camden, NJ, 08103, USA (2) Divisions of Cardiovascular Disease and Critical Care Medicine, Department of Medicine, UMDNJ-Robert Wood Johnson Medical School at Camden, Cooper University Hospital, Camden, NJ, USA (3) Department of Surgery, UMDNJ-Robert Wood Johnson Medical School at Camden, Cooper University Hospital, Camden, NJ, USA (4) Department of Emergency Medicine, Beth Israel Deaconess Medical Center, Boston, MA, USA Article History: Registration Date: 18/05/2009 Received Date: 04/06/2008 Accepted Date: 26/04/2009 Online Date: 24/06/2009 Article note: On behalf of the Microcirculatory Alterations in Resuscitation and Shock (MARS) Investigators. Electronic supplementary material The online version of this article (doi: 10.1007/s00134-009-1517-1) contains supplementary material, which is available to authorized users.

Recent experimental results have shown that effects such as dispersion and cardiac pulsation have a significant effect on the arterial spin labeling (ASL) signal. These have not been incorporated into the existing ASL models potentially leading to inaccuracies in flow calculation. In this study, we develop a new model, based on physical principles, to model the transit of the ASL signal from the tagging band to the imaging band using the mass transport equation. We relax the assumption of a uniform plug flow, and account for the dispersion caused by the viscous nature of blood. The model also provides a framework within which other physiological aspects can easily be examined. Here, we examine the effects of flow dispersion on the ASL signal, and hence the quantification of cerebral perfusion. Our results suggest that not accounting for flow dispersion may result in inaccurate values of cerebral perfusion. Index Terms--Arterial spin labeling (ASL), cerebral blood flow (CBF), flow dispersion, magnetic resonance imaging, perfusion.

Previous study suggests that with evolution of the metabolic syndrome, patterns of arteriolar reactivity are profoundly altered and may constrain functional hyperemia. This study investigated interactions between parameters of vascular reactivity at two levels of resistance arterioles in obese Zucker rats (OZR), translating these observations into perfusion regulation for in situ skeletal muscle. Dilation of isolated and in situ resistance arterioles from OZR to acetylcholine, arachidonic acid (AA), and hypoxia (isolated arterioles only) were blunted vs. lean Zucker rats (LZR), although dilation to adenosine was intact. Increased adrenergic tone (phenylephrine) or intralumenal pressure (ILP) impaired dilation in both strains (OZR>LZR). Treatment of OZR arterioles with Tempol (superoxide dismutase mimetic) or SQ-29548 (prostaglandin [H.sub.2]/thromboxane [A.sub.2] receptor antagonist) improved dilator reactivity under control conditions and with increased ILP, but had minimal effect with increased adrenergic tone. Arteriolar dilation to adenosine was well maintained in both strains under all conditions. For in situ cremasteric arterioles, muscle contraction-induced elevations in metabolic demand elicited arteriolar dilations and hyperemic responses that were blunted in OZR vs. LZR, although distal parallel arterioles were characterized by heterogeneous dilator and perfusion responses, [alpha]-Adrenoreceptor blockade improved outcomes at rest but had minimal effect with elevated metabolic demand. Treatment with Tempol or SQ-29548 had minimal impact at rest, but lessened distal arteriolar perfusion heterogeneity with increased metabolic demand. In blood-perfused gastrocnemius of OZR, perfusion was constrained primarily by adrenergic tone, while myogenic activation and endothelium-dependent dilation did not appear to contribute significantly to ischemia. These results of this novel, integrated approach suggest that adrenergic tone and metabolic dilation are robust determinants of bulk perfusion to skeletal muscle of OZR, while endothelial dysfunction may more strongly regulate perfusion distribution homogeneity via the impact of oxidant stress and AA metabolism. peripheral vascular disease; microcirculation; regional blood flow; obesity

Many experimental studies concerning nitric oxide (NO) release from endothelium and its vasodilative action are available in the literature, but no analytical description or modeling of these phenomena can be found. On the contrary, a large modeling literature is available concerning the other cardiovascular control mechanisms, such as the myogenic and metabolic control. In order to analytically describe these phenomena, a model of the endothelial control (defined in the Laplace domain and based on experimental data) was implemented and integrated with a lumped-parameter model of the systemic circulation, consisting of large artery segments and peripheral networks. The endothelial regulation model was based on the hypothesis proposed by Kuchan and Frangos, considering that NO release from the endothelium is generated by two parallel paths. The whole model was then applied to study the different vascular constriction or dilation under continuous or pulsatile perfusion, in order to better understand the clinical evidences of a poor organ perfusion in the presence of continuous with respect to pulsatile cardiopulmonary bypass. According to the experimental evidences, the main results obtained from the model revealed a widespread vascular constriction under continuous perfusion with respect to pulsatile. This result remains constant in the presence of different conditions of blood parameters and flow waveform. Index Terms--Cardiopulmonary bypass, endothelial control, lumped-parameter model, nitric oxide (NO).

Conventional pulse oximetry has limited accuracy in measuring blood oxygen saturation in low-saturation and -perfusion scenarios. This limits the application of pulse oximetry in patients suffering from peripheral vascular afflictions. We present a novel pulse oximetry system that proposes solutions to these low-saturation and -perfusion scenarios by inducing an artificial pulse in the detected photoplethysmograph (PPG). A novel arteriovenous hypothesis was formulated to extract arterial and venous saturation data from the artificial PPG using arterial-to-venous compliance ratios. Sensor wavelengths were selected to provide high- and low-saturation accuracy, followed by an in vitro sensor calibration procedure. System performance was validated by means of an in vivo procedure. In vivo results indicate good accuracy for high saturation, with limited accuracy in low-saturation scenarios. The arteriovenous hypothesis was validated, indicating that venous saturation can be extracted from the artificial PPG. The results indicate that the proposed system might be able to accurately monitor arterial and venous saturation in low- or no-perfusion scenarios. It is recommended that further studies into the system's performance are conducted. Index Terms--In vitro calibration, low perfusion, low saturation, photon diffusion theory, pulse oximetry, venous saturation.

A microfluidic perfusion system was developed for automated delivery of stimulant waveforms to cells within the device. The 3-layer glass/polymer device contained two pneumatic pumps, a 12 cm mixing channel, and a 0.2 [micro]L cell chamber. By altering the flow rate ratio of the pumps, a series of output concentrations could be produced while a constant 1.43 [+ or -] 0.07 [micro]L/min flow rate was maintained. The output concentrations could be changed in time producing step gradients and other waveforms, such as sine and triangle waves, at different amplitudes and frequencies. Waveforms were analyzed by comparing the amplitude of output waveforms to the amplitude of theoretical waveforms. Below a frequency of 0.0098 Hz, the output waveforms had less than 20% difference than input waveforms. To reduce backflow of solutions into the pumps, the operational sequence of the valving program was modified, as well as differential etching of the valve seat depths. These modifications reduced backflow to the point that it was not detected. Gradients in glucose levels were applied in this work to stimulate single islets of Langerhans. Glucose gradients between 3 and 20 mM brought clear and intense oscillations of intracellular [[Ca.sup.2+]] indicating the system will be useful in future studies of cellular physiology.

Byline: Vincenzo Cantaluppi (1,2), Barbara Assenzio (3), Daniela Pasero (3), Giuseppe Mauriello Romanazzi (1), Alfonso Pacitti (2), Giacomo Lanfranco (2), Valeria Puntorieri (3), Erica L. Martin (3), Luciana Mascia (3), Gianpaola Monti (4), Giampaolo Casella (4), Giuseppe Paolo Segoloni (2), Giovanni Camussi (1,2), V. Marco Ranieri (3) Keywords: Sepsis; Acute renal failure; Lipopolysaccharide; Apoptosis Abstract: Objective To test the hypothesis that extracorporeal therapy with polymyxin B (PMX-B) may prevent Gram-negative sepsis-induced acute renal failure (ARF) by reducing the activity of proapoptotic circulating factors. Setting Medical-Surgical Intensive Care Units. Patients and interventions Sixteen patients with Gram-negative sepsis were randomized to receive standard care (Surviving Sepsis Campaign guidelines) or standard care plus extracorporeal therapy with PMX-B. Measurements and results Cell viability, apoptosis, polarity, morphogenesis, and epithelial integrity were evaluated in cultured tubular cells and glomerular podocytes incubated with plasma from patients of both groups. Renal function was evaluated as SOFA and RIFLE scores, proteinuria, and tubular enzymes. A significant decrease of plasma-induced proapoptotic activity was observed after PMX-B treatment on cultured renal cells. SOFA and RIFLE scores, proteinuria, and urine tubular enzymes were all significantly reduced after PMX-B treatment. Loss of plasma-induced polarity and permeability of cell cultures was abrogated with the plasma of patients treated with PMX-B. These results were associated to a preserved expression of molecules crucial for tubular and glomerular functional integrity. Conclusions Extracorporeal therapy with PMX-B reduces the proapoptotic activity of the plasma of septic patients on cultured renal cells. These data confirm the role of apoptosis in the development of sepsis-related ARF. Author Affiliation: (1) Dipartimento di Medicina Interna, Centro Ricerca Medicina Sperimentale (CeRMS), Torino, Italy (2) Ospedale S. Giovanni Battista-Molinette, SCDU Nefrologia, Dialisi e Trapianti Universita di Torino, Torino, Italy (3) Dipartimento di Anestesiologia e Rianimazione, Ospedale S. Giovanni Battista-Molinette, Universita di Torino, Corso Dogliotti 14, 10126, Torino, Italy (4) Ospedale Niguarda, Servizio di Anestesia e Rianimazione, Milano, Italy Article History: Registration Date: 11/04/2008 Received Date: 21/11/2007 Accepted Date: 02/04/2008 Online Date: 08/05/2008 Article note: Supported by Italian Ministry of University and Research (COFIN 4657/06-08), Regione Piemonte (integrated project A47, Ministry of Health (Ricerca Finalizzata 02), and Fondazione S. Paolo (Progetto S. Paolo). Barbara Assenzio, Vincenzo Cantaluppi, and Daniela Pasero equally contributed to the manuscript and should all be considered as first author. Electronic supplementary material The online version of this article (doi: 10.1007/s00134-008-1124-6) contains supplementary material, which is available to authorized users.

The determination of the presence of nitric oxide metabolites in the rat vitreous cavity in a regioselective manner is complicated by the size and shape of the eye as well as the diffusivity of the molecule and its metabolites. In this work, in vivo low-flow push-pull perfusion sampling was utilized with a rapid capillary electrophoretic assay to monitor levels of the major NO metabolite, nitrate, at the vitreoretinal interface (VRI) of normal and aged rat models. The sampling probe tips were placed in three different positions in the posterior chamber through a 29-gauge guide needle. Sampling was performed along the VRI over the optic nerve head and regions peripheral to the optic nerve head. Additionally, samples were collected from the middle vitreous region to compare to VRI sampling. A significant (P < 0.05) difference in the perfusate nitrate concentration was observed in each location, which may be due to the source of NO production or the clearance mechanism of the molecule from the vitreous cavity. Infusion of L-NAME with physiological saline led to a significant decrease (35%) in the observed nitrate level. LFPPP was then utilized to observe nitrate levels after an average of 4.5 months of aging. A 3-fold increase in the mean level of nitrate over the optic nerve head was observed in mature animals compared to younger control animals. Precise measurement of NO metabolites along the VRI may provide insights into the function of NO in maintaining homeostatic conditions and the molecular changes at the diseased retina.

The underlying mechanism(s) of improved left ventricular function (LV) due to mesenchymal stem cell (MSC) administration after myocardial infarction (MI) remains highly controversial. Myocardial regeneration and neovascularization, which leads to increased tissue perfusion, are proposed mechanisms. Here we demonstrate that delivery of MSCs 3 days after MI increased tissue perfusion in a manner that preceded improved LV function in a porcine model. MI was induced in pigs by 60-min occlusion of the left anterior descending coronary artery, followed by reperfusion. Pigs were assigned to receive intramyocardial injection of allogeneic MSCs (200 million, ~15 injections) (n = 10), placebo (n = 6), or no intervention (n = 8). Resting myocardial blood flow (MBF) was serially assessed by first-pass perfusion magnetic resonance imaging (MRI) over an 8-wk period. Over the first week, resting MBF in the infarct area of MSC-treated pigs increased compared with placebo-injected and untreated animals [0.17 [+ or -] 0.03, 0.09 [+ or -] 0.01, and 0.08 [+ or -] 0.01, respectively, signal intensity ratio of MI to left ventricular blood pool (LVBP); P < 0.01 vs. placebo, P < 0.01 vs. nontreated]. In contrast, the signal intensity ratios of the three groups were indistinguishable at weeks 4 and 8. However, MSC-treated animals showed larger, more mature vessels and less apoptosis in the infarct zones and improved regional and global LV function at week 8. Together these findings suggest that an early increase in tissue perfusion precedes improvements in LV function and a reduction in apoptosis in MSC-treated hearts. Cardiac MRI-based measures of blood flow may be a useful tool to predict a successful myocardial regenerative process after MSC treatment. myocardial blood flow; perfusion magnetic resonance image; neovascularization; myocardial infarction; allogeneic

Prostaglandin (PG)E derivatives are widely used for treating gastric mucosal injury. PGE receptors are classified into four subtypes, [EP.sub.1] [EP.sub.2], [EP.sub.3], and [EP.sub.4]. We have tested which EP receptor subtypes participate in gastric mucosal protection against ethanol-induced gastric mucosal injury and clarified the mechanisms of such protection. The gastric mucosa of anesthetized rats was perfused at 2 ml/min with physiological saline, agonists for [EP.sub.1], [EP.sub.2], [EP.sub.3], and [EP.sub.4], or 50% ethanol, using a constant-rate pump connected to a cannula placed in the esophagus. The gastric microcirculation of the mucosal base of anesthetized rats was observed by transillumination through a window made by removal of the adventitia and muscularis externa. [PGE.sub.2] and subtypespecific EP agonists were applied to the muscularis mucosae at the window. Application of 50% ethanol dilated the mucosal arterioles and constricted the collecting venules. Collecting venule constriction by ethanol was completely inhibited by [PGE.sub.2] and by [EP.sub.2] and [EP.sub.4] agonists (100 nM) but not by an [EP.sub.1] or an [EP.sub.3] agonist. Ethanolinduced mucosal injury was also inhibited by [EP.sub.2] and [EP.sub.4] agonists. When leukotriene (LT)[C.sub.4] levels in the perfusate of the gastric mucosa were determined by ELISA, intragastric ethanol administration elevated the [LTC.sub.4] levels sixfold from the basal levels. These elevated levels were significantly (60%) reduced by both [EP.sub.2] and [EP.sub.4] agonists but not by other EP agonists. Since [LTC.sub.4] application at the window constricted collecting venules strongly, and an LTC antagonist reduced ethanol-induced mucosal injury, reductions in LTC4 generation in response to [EP.sub.2] and [EP.sub.4] receptor signaling may be relevant to the protective action of [PGE.sub.2]. The present results indicate that [EP.sub.2] and [EP.sub.4] receptor signaling inhibits ethanol-induced gastric mucosal injury through cancellation of collecting venule constriction by reducing [LTC.sub.4] production. prostaglandin [E.sub.2]; EP receptor; gastric microcirculation; gastric perfusion

Production of urine is initiated by fluid and solute flux across the glomerular filtration barrier. Recent ultrastructural studies have shown that under extreme conditions of no filtration, or very high filtration, a restriction to flow is predicted in a space underneath the podocyte cell body or its processes, the subpodocyte space (SPS). The SPS covered up to two-thirds of the glomerular filtration barrier (GFB) surface. The magnitude of this restriction to flow suggested that it might be unlikely that filtration into and flow through the SPS would contribute significantly to total flow across the entire GFB under these conditions. To determine whether the SPS has similar properties under normal physiological conditions, we have carried out further three-dimensional reconstruction of rat glomeruli perfused at physiologically normal hydrostatic and colloid osmotic pressures. These reconstructions show that the sub-podocyte space is even more restricted under these conditions, with a mean height of the SPS of 0.34 [micro]m, mean pathlength of 6.7 [+ or -] 1.4 [micro]m, a mean width of the SPS exit pore of 0.15 [+ or -] 0.05 [micro]m, and length of 0.25 [+ or -] 0.05 [micro]m. Mathematical modeling of this SPS based on a circular flow model predicts that the resistance of these dimensions is 2.47 times that of the glomerular filtration barrier and exquisitely sensitive to changes in the dimensions of the SPS exit pore (SEP), indicating that the SEP could be the principal regulator of the extravascular pressure in the SPS. This suggests a physiological role of the podocyte in the regulation of glomerular fluid flux across most of the GFB. glomerular filtration barrier; podocyte; mathematical modeling

Vascular endothelium regulates vascular tone and tissue perfusion in response to various physiological and pathological stimuli. Insulin and meal feeding increase microvascular perfusion and thus oxygen, nutrient, and hormone delivery to human skeletal muscle. Meal feeding also increases cardiac microvascular perfusion in healthy humans. To examine whether insulin at physiological concentrations increases microvascular perfusion in human myocardium, we studied 13 healthy, overnight-fasted, lean, young human volunteers by using myocardial contrast echocardiography (MCE) and insulin-clamp techniques. We measured cardiac microvascular blood volume (MBV), microvascular flow velocity (MFV), and microvascular blood flow (MBF) at baseline, 60 min, and 120 min after initiating insulin infusion at 1 mU x [kg.sup.-1] x [min.sup.-1]. MBF is the product of MBV and MFV and represents microvascular perfusion. Insulin increased myocardial MBV by 23% at 60 min (P < 0.01) and by 41% at 120 min (P = 0.001) without changing MFV. As a result, insulin-mediated myocardial MBF increased significantly at both 60 min (P < 0.01) and 120 min (P < 0.0005). Insulin also significantly increased brachial artery diameter, flow velocity, and total blood flow at 60 and 120 min (P < 0.05 for all). The changes in cardiac MBV correlated positively with quantitative insulin sensitivity check index (QUICKI) and negatively with body mass index but not with the steady-state glucose-infusion rates or the changes in brachial artery parameters. We conclude that insulin, at physiologically relevant concentrations, increases microvascular perfusion in human heart muscle by increasing cardiac MBV in healthy, insulin-sensitive adults. This insulin-mediated cardiac microvascular perfusion may play an important role in normal human myocardial oxygen and substrate physiology. heart; myocardial contrast echocardiography; microvascular blood flow; insulin clamp

The enzyme lipoprotein lipase (LPL) releases fatty acids from lipoprotein triglycerides for use in cell metabolism. LPL activity is rapidly modulated in a tissuespecific manner. Recent studies have shown that in rat adipose tissue this occurs by a shift of extracellular LPL toward an inactive form catalyzed by an LPL-controlling protein whose expression changes in response to the nutritional state. To explore whether a similar mechanism operates in other tissues we injected actinomycin D to block transcription of the putative LPL controlling protein(s). When actinomycin was given to fed rats, heparin-releasable LPL activity increased by 160% in heart and by 150% in a skeletal muscle (soleus) in 6 h. Postheparin LPL activity in blood increased by about 200%. To assess the state of extracellular LPL we subjected the spontaneously released LPL in heart perfusates to chromatography on heparin-agarose, which separates the active and inactive forms of the lipase. The amount of lipase protein released remained relatively constant on changes in the nutritional state and/or blockade of transcription, but the distribution between the active and inactive forms changed. Less of the LPL protein was in the active form in perfusates from hearts from fed compared with fasted rats. When glucose was given to fasted rats the proportion of LPL protein in the active form decreased. Actinomycin D increased the proportion that was active, in accord with the hypothesis that the message for a rapidly turning over LPL-controlling protein was being removed. muscle; heart perfusion; postheparin plasma; heparin; actinomycin D

Fatty acid translocase (FAT)/CD36 is involved in regulating the uptake of long-chain fatty acids into muscle cells. However, the contribution of FAT/CD36 to fatty acid metabolism remains unknown. We examined the role of FAT/CD36 on fatty acid metabolism in perfused muscles (soleus and red and white gastrocnemius) of wild-type (WT) and FAT/CD36 null (KO) mice. In general, in muscles of KO mice, 1) insulin sensitivity and 5-aminoimidazole-4-carboxamide-1-[beta]-D-ribofuranoside (AICAR) sensitivity were normal, 2) key enzymes involved in fatty acid oxidation were altered minimally or not at all, and 3) except for an increase in soleus muscle FATP1 and FATP4, these fatty acid transporters were not altered in red and white gastrocnemius muscles, whereas plasma membrane-bound fatty acid binding protein was not altered in any muscle. In KO muscles perfused under basal conditions (i.e., no insulin, no AICAR), rates of hindquarter fatty acid oxidation were reduced by 26%. Similarly, in oxidative but not glycolytic muscles, the basal rates of triacylglycerol esterification were reduced by 40%. When muscles were perfused with insulin, the net increase in fatty acid esterification was threefold greater in the oxidative muscles of WT mice compared with the oxidative muscles in KO mice. With AICAR-stimulation, the net increase in fatty acid oxidation by hindquarter muscles was 3.7-fold greater in WT compared with KO mice. In conclusion, the present studies demonstrate that FAT/CD36 has a critical role in regulating fatty acid esterification and oxidation, particularly during stimulation with insulin or AICAR. perfusion; palmitate; esterification; oxidation; fatty transport proteins 1 and 2; plasma membrane-bound fatty acid binding protein; 5-amino-imidazole-4-carboxamide-1-[beta]-D-ribofuranoside doi:10.1152/ajpendo.00579.2006.

The objective of this work was to evaluate the influence of exogenous L-arginine on the capillary blood flow of peripheral tissues of normotensive subjects. Rats were anesthetized with sodium pentobarbital, and the blood flow of femoral, dorsal, and ventral skin and gastrocnemius and soleus muscle was measured by laser Doppler flow and microsphere methods to compare the blood flow before and after the L-arginine infusion. L-Arginine lowered the mean blood pressure in a dose-dependent manner, but a statistically significant reduction in mean blood pressure was detected only at a high dose of 500 mg/kg of body weight. The significant blood flow increment was detected after the L-arginine infusion at doses of 50 and 150 mg/kg without causing hypotension. Nicardipine, a calcium channel blocker, also increased the skin blood flow, but the blood flow increment and blood pressure fall were comparable. A significant increment in microperfusion was detected in gastrocnemius, soleus muscle, and ventral skin compared with control group by the microsphere method. No adverse effects were observed during L-arginine and microsphere infusion. The present work indicates that L-arginine infusion increases muscle capillary blood flow in rats that are not performing exercise. Supplementation with L-arginine might provide additional blood flow at rest and during exercise and result in the improvement of muscle performance and exercise capacity. exercise | nitric oxide

ST-segment depression is commonly seen in patients with acute coronary syndromes. Most authors have attributed it to transient reductions in coronary blood flow due to nonocclusive thrombus formation on a disrupted atherosclerotic plaque and dynamic focal vasospasm at the site of coronary artery stenosis. However, ST-segment depression was never reproduced in classic animal models of coronary stenosis without the presence of tachycardia. We hypothesized that ST-segment depression occurring during acute coronary syndromes is not entirely explained by changes in epicardial coronary artery resistance and thus evaluated the effect of a slow, progressive epicardial coronary artery occlusion on the ECG and regional myocardial blood flow in anesthetized pigs. Slow, progressive occlusion over 72 min (SD 27) of the left anterior descending coronary artery in 20 anesthetized pigs led to a 90% decrease in coronary blood flow and the development of ST-segment elevation associated with homogeneous and transmural myocardial blood flow reductions, confirmed by microspheres and myocardial contrast echocardiography. ST-segment depression was not observed in any ECG lead before the development of ST-segment elevation. At normal heart rates, progressive epicardial stenosis of a coronary artery results in myocardial ischemia associated with homogeneous, transmural reduction in regional myocardial blood flow and ST-segment elevation, without preceding ST-segment depression. Thus, in coronary syndromes with ST-segment depression and predominant subendocardial ischemia, factors other than mere increases in epicardial coronary resistance must be invoked to explain the heterogeneous parietal distribution of flow and associated ECG changes. ST-segment elevation; epicardial resistance; myocardial perfusion

The hamster window chamber model was used to study systemic and microvascular hemodynamic responses to extreme hemodilution with low- and high-viscosity plasma expanders (LVPE and HVPE, respectively) to determine whether plasma viscosity is a factor in homeostasis during extreme anemic conditions. Moderated hemodilution was induced by two isovolemic steps performed with 6% 70-kDa dextran until systemic hematocrit (Hct) was reduced to 18% (level 2). In a third isovolemic step, hemodilution with LVPE (6% 70-kDa dextran, 2.8 cP) or HVPE (6% 500-kDa dextran, 5.9 cP) reduced Hct to 11%. Systemic parameters, cardiac output (CO), organ flow distribution, microhemodynamics, and functional capillary density, were measured after each exchange dilution. Fluorescent-labeled microspheres were used to measure organ (brain, heart, kidney, liver, lung, and spleen) and window chamber blood flow. Final blood and plasma viscosities after the entire protocol were 2.1 and 1.4 cP, respectively, for LVPE and 2.8 and 2.2 cP, respectively, for HVPE (baseline = 4.2 and 1.2 cP, respectively). HVPE significantly elevated mean arterial pressure and CO compared with LVPE but did not increase vascular resistance. Functional capillary density was significantly higher for HVPE [87% (SD 7) of baseline] than for LVPE [42% (SD 11) of baseline]. Increases in mean arterial blood pressure, CO, and shear stressmediated factors could be responsible for maintaining organ and microvascular perfusion after exchange with HVPE compared with LVPE. Microhemodynamic data corresponded to microsphere-measured perfusion data in vital organs. microcirculation; extreme hemodilution; plasma expander; organ flow distribution; intravascular oxygen; functional capillary density

Blood perfusion in organs has been shown to be heterogeneous in a number of cases. At the same time, a number of models of vascular structure and flow have been proposed that also generate heterogeneous perfusion. Although a relationship between local perfusion and vascular structure has to exist, no model has yet been validated as an accurate description of this relationship. A study of perfusion and three-dimensional (3D) arterial structure in individual rat kidneys is presented, which allows comparison between local measurements of perfusion and model-based predictions. High-resolution computed tomography is used to obtain images of both deposited microspheres and of an arterial cast in the same organ. Microsphere deposition is used as an estimate of local perfusion. A 3D cylindrical pipe model of the arterial tree is generated based on an image of the arterial cast. Results of a flow model are compared with local microsphere deposition. High correlation ([r.sup.2] > 0.94) was observed between measured and modeled flows through the vascular tree segments. However, the relative dispersion of the microsphere perfusion measurement was two- to threefold higher than perfusion heterogeneity calculated in the flow model. Also, there was no correlation in the residual deviations between the methods. This study illustrates the importance of comparing models of local perfusion with in vivo measurements of perfusion in the same biologically realistic vascular tree. perfusion heterogeneity; three-dimensional imaging; microcomputed tomography; casting; rat kidney; blood flow

Tissue engineering is one approach to address the donor-organ shortage, but to attain clinically significant viable cell densities in thick tissues, laboratory-constructed tissues must have an internal vascular supply. We have adopted a biomimetic approach and assembled microscale modular components, consisting of submillimeter-sized collagen gel rods seeded with endothelial cells (ECs) into a (micro)vascularized tissue; in some prototypes the gel contained HepG2 cells to illustrate the possibilities. The EC-covered modules then were assembled into a larger tube and perfused with medium or whole blood. The interstitial spaces among the modules formed interconnected channels that enabled this perfusion. Viable cell densities were high, within an order of magnitude of cell densities within tissues, and the percolating nature of the flow through the construct was evident in microcomputed tomography and Doppler ultrasound measurements. Most importantly, the ECs retained their nonthrombogenic phenotype and delayed clotting times and inhibited the loss of platelets associated with perfusion of whole blood through the construct. Unlike the conventional scaffold and cell-seeding paradigm of other tissue-engineering approaches, this modular construct has the potential to be scalable, uniform, and perfusable with whole blood, circumventing the limitations of other approaches. collagen gel modules | endothelial cells | tissue engineering

Hypertension is associated with increased levels of oxidative stress and medullary renal injury. Previous studies have shown that elevations in renal perfusion pressure increase [Na.sup.+] delivery to the medullary thick ascending limb (mTAL), and enhancement of NaCl transport in the outer medulla has been reported in many experimental forms of hypertension. This study examined the effects of increased [Na.sup.+] and fluid delivery in mTAL perfused in vitro on the generation of superoxide. Osmolality was maintained constant between low- and high-[Na.sup.+] perfusates by adjusting with choline [Cl.sup.-]. Real-time fluorescent microscopic techniques were used to determine the generation of superoxide and nitric oxide in individual mTAL cells using dihydroethidium and DAF-FM dyes, respectively. Increasing the [Na.sup.+] concentration of the perfusate from 60 to 149 mM or luminal flow rate from 5 to 20 nl/min (with fixed [Na.sup.+] concentration of 60 mM) significantly increased superoxide generation and decreased nitric oxide in mTAL. These effects were inhibited when active transport of [Na.sup.+] was inhibited by ouabain. We conclude that increases in luminal [Na.sup.+] concentration and/or flow rate can increase the generation of superoxide in mTAL and reduce nitric oxide bioavailability. This may lead to reduction in medullary blood flow and promote hypoxia and tubular necrosis within the renal medulla during in hypertension. hypertension; renal perfusion pressure doi:10.1152/ajprenal.00407.2005

The sudden exposure of veins to arterial pressures during coronary venous retroperfusion may cause rupture of small venules. Our rationale is to first occlude the coronary vein, which will cause an increase in pressure intermediate to arterial and venous values, and hence lead to remodeling and increased wall thickness of the veins prior to retroperfusion. To accomplish this objective, five pigs were subjected to left anterior descending (LAD) vein ligation while six pigs served as sham. Myocardial tissue samples were obtained from the area adjacent to the LAD vein at four transmural locations of the left ventricular free wall: epicardial surface, subepicardium, midmyocardium, and endocardium. Arterioles and venules from the experimental and sham control groups were photographed, and the following measurements were made: inner and outer circumferences, inner and outer areas, major and minor diameters, and intima-media thickness. Each vessel was categorized in tour different orders according to lumen diameter. Our results show that intima-media thickness was larger in the experimental group in all four regions of the heart and in all four orders of the vessels, although venules from the epicardial region showed the largest increase in thickness. The intima-media thickness-to-radius ratio was also larger in the experimental group and decreased from epicardial to endocardial region of the heart and from order 1 to order 4 of the vessels. The present study provides a rationale for the development of coronary retroperfusion strategy that avoids vessel rupture and hemorrhage in the postcapillary venules. pressure overload; arterialization; rupture stress; remodeling; ligation doi:10.1152/ajpheart.00235.2006

The aim of this study was to determine the contribution of neuropeptide Y (NPY) [Y.sub.1] receptors in neurally mediated reductions in renal medullary perfusion. In pentobarbital sodium-anesthetized rabbits, electrical stimulation of the renal nerves (RNS, 0.5-16 Hz) decreased renal perfusion in a frequency-dependent manner. Under control conditions, 4 Hz reduced cortical and medullary perfusion by -85 [+ or -] 3% and -43 [+ or -] 7%, whereas 8 Hz reduced them by -93 [+ or -] 2% and -73 [+ or -] 4%, respectively. After [Y.sub.1] receptor antagonism with BIBO3304TF (0.1 mg/kg plus 0.2 mg*[kg*.sup.-1][h.sup.-1]), RNS reduced perfusion less (by -65 [+ or -] 9% and -12 [+ or -] 8% at 4 Hz). [[alpha].sub.1]-Adrenoceptor antagonism with prazosin (0.2 mg/kg plus 0.2 mg [kg.sup.-1][h.sup.-1]) also inhibited RNS-induced reductions in renal perfusion (-80 [+ or -] 4% and -37 [+ or -] 10% reductions in the cortex and medulla, respectively, at 8 Hz). When given after BIBO3304TF treatment, prazosin inhibited RNS-induced reductions in cortical and medullary perfusion more profoundly (-57 [+ or -] 12% and -25 [+ or -] 9% reductions, respectively, at 8 Hz). [Y.sub.1] receptor- and [[alpha].sub.1]-adrenoceptor-blockade were confirmed by testing vascular responses to renal arterial NPY and phenylephrine boluses. NPY-positive immunolabeling was observed around interlobular arteries, afferent and efferent arterioles, and in the outer medulla. In conclusion, [Y.sub.1] receptors and [[alpha].sub.1]-adrenoceptors contribute to RNS-induced vasoconstriction in the vessels that control both cortical and medullary perfusion. Consistent with this, NPY immunostaining was associated with blood vessels that control perfusion in both regions. There also seems to be an interaction between [Y.sub.1] receptors and [[alpha].sub.1]-adrenoceptor-mediated neurotransmission in the control of renal perfusion. renal medullary blood flow; sympathetic nervous system; BIBO3304TF

In vitro evidence suggests that intraluminal nucleotides, acting on apical P2 receptors, may influence amiloride-sensitive sodium reabsorption in collecting ducts. The present study has assessed this possibility directly in anesthetized rats, by determining the urinary recovery of 22Na relative to that of [[sup.14]C]inulin (Na/inulin recovery ratio) during in vivo microperfusion of late distal tubules with artificial tubular fluid containing various P2 agonists (all at 1 mM). In animals maintained on a control diet, in which amiloride-sensitive [sup.22]Na reabsorption was modest, the poorly hydrolysable, broad-spectrum P2 agonist ATP[gamma]/S had no significant effect on the Na/inulin recovery ratio. In contrast, in rats maintained on a low-sodium diet, in which amiloride-sensitive [sup.22]Na reabsorption was considerably enhanced, ATP[gamma]/S caused a significant increase in the Na/inulin recovery ratio (control: 14 [+ or -] 3%; ATP[gamma]S: 28 [+ or -] 4%: n = 32 pairs; P < 0.001, paired t-test). No change in the Na/inulin recovery ratio was seen in time controls (13 [+ or -] 3 vs. 14 [+ or -] 4%; n = 15 pairs). In subsequent experiments in rats maintained on a low-sodium diet, we used more selective agonists in an attempt to identify the receptor subtype responsible for the effect of ATP[gamma]S. The P2[Y.sub.1] agonist 2meSADP, the P2[Y.sub.2/4] agonists [Ap.sub.4]A and [Cp.sub.4]U, and the P2X agonist BzATP were all without significant effect on the Na/inulin recovery ratio. These findings constitute the first in vivo evidence for a functional role for apical P2 receptors in collecting ducts, but the identity of the receptor subtype(s) involved remains elusive. purinoceptors; in vivo microperfusion; ATP[gamma]/S

Arteriolar arcades provide alternate pathways for blood flow after obstruction of arteries or arterioles such as occurs in stroke and coronary and peripheral vascular disease. When obstruction is prolonged, remaining vessels adjust their diameters chronically in response to altered hemodynamic and metabolic conditions. Here, the effectiveness of arcades in maintaining perfusion both immediately following obstruction and after structural adaptation was examined. Morphometric data from a vascular casting of the pig triceps brachii muscle and published data were used to develop a computational model for the hemodynamics and structural adaptation of the arcade network between two feed artery branches, FA1 and FA2. The predicted total flow to capillaries ([Q.sub.TA]) in the region initially supplied by FA2 decreased to 26% of the normal value immediately after FA2 obstruction but was restored to 78% of the normal value after adaptation. After obstruction of 1-10 randomly selected arcade segments, [Q.sub.TA] was on average 18% higher in the arcade network than in a corresponding two-tree network without arcades. Structural adaptation increased [Q.sub.TA] by an additional 16% in the arcade network but had almost no effect in the two-tree network. These results indicate that arcades can partially maintain blood flow after vascular blockage and that this effect is substantially enhanced by structural adaptation. collateralization; computational model; blood flow; shear stress

Chronic coronary artery stenosis results in patchy necrosis in the dependent myocardium and impairs global and regional left ventricular (LV) function in rats in vivo. The aim of the present study was to compare regional myocardial blood flow (RMBF) and function (F) in poststenotic myocardium by using magnetic resonance imaging (MRI) and to compare MRI blood flow changes to histological alterations to assess whether RMBF m the viable poststenotic tissue remains normal. MRI was performed in 11 anesthetized Wistar rats with 2-wk stenosis of the left coronary artery. Postmortem, the extent of fibrotic tissue was quantified. Poststenotic RMBF was significantly reduced to 2.21 [+ or -] 0.30 ml * [g.sup.-1] * min.sup.-1] compared with RMBF in the remote myocardium (4.05 [+ or -] 0.50 ml * [g.sup.-1] * [min.SUP.-1]). A significant relationship between the poststenotic RMBF (%remote area) and the poststenotic F (%remote myocardium) was calculated (r = 0.61, P < 0.05). Assuming perfusion in scar tissue to be 32 [+ or -] 5% of perfusion of remote myocardium, as measured in five additional rats, and that in remote myocardium to be 114 [+ or -] 25% of that in normal myocardium, as assessed in five sham rats, the calculated perfusion in partially fibrotic tissue samples (35.7 [+ or -] 5.2% of analyzed area) was 2.88 [+ or -] 0.18 ml * [g.sup.-1] * min.sup.-], whereas measured MRI perfusion was only 1.86 [+ or -] 0.24 ml * [g.sup.-1] * min.sup.-] (P < 0.05). These results indicate that resting perfusion in viable poststenotic myocardium is moderately reduced. Alterations in global and regional LV function are therefore secondary to both patchy fibrosis and reduced resting perfusion. ischemic cardiomyopathy; necrosis

Hearts with overexpression of anchored lipoprotein lipase (LpL) by cardiomyocytes (hLp[L.sup.GPI] mice) develop a lipotoxic cardiomyopathy. To characterize cardiac fatty acid (FA) and triglyceride (TG) metabolism in these mice and to determine whether changes in lipid metabolism precede cardiac dysfunction, hearts from young mice were perfused in Langendorff mode with [[sup.14]C]palmitate. In hLp[L.sup.GPI] hearts, FA uptake and oxidation were decreased by 59 and 82%, respectively. This suggests reliance on an alternative energy source, such as TG. Indeed, these hearts oxidized 88% more TG. Hearts from young hLp[L.sup.GPI] mice also had greater uptake of intravenously injected cholesteryl ester-labeled Intralipid and VLDL. To determine whether perfusion of normal hearts would mimic the metabolic alterations found in hLp[L.sup.GPI] mouse hearts, wild-type hearts were perfused with [[sup.14]C] palmitate and either human VLDL or Intralipid (0.4 mM TG). Both sources of TG reduced [[sup.14]C] palmitate uptake (48% with VLDL and 45% with Intralipid) and FA oxidation (71% with VLDL and 65% with Intralipid). Addition of either heparin or LpL inhibitor P407 to Intralipid-containing perfusate restored [[14.sup.C]]palmitate uptake and confirmed that Intralipid inhibition requires local LpL. Our data demonstrate that reduced FA uptake and oxidation occur before mechanical dysfunction in hLp[L.sup.GPI] lipotoxicity. This physiology is reproduced with perfusion of hearts with TG-containing particles. Together, the results demonstrate that cardiac uptake of TG-derived FA reduces utilization of albumin-FA. lipotoxicity; triglyceride; fatty acid metabolism; lipoprotein lipase

The purpose of this study was to test the hypothesis that exchange transfusion with liposomal hemoglobin (LH) reduces the microheterogeneity of regional myocardial flows while sustaining cardiac function. Neo Red Cell mixed with albumin was used as the LH solution, in which the LH volume fraction was 17~18% and hemoglobin density was nearly two-thirds smaller than in rat blood. Regional myocardial flows in left ventricular free walls were measured by tracer digitalradiography (100-[micro]m resolution) in anesthetized rats with or without 50% blood-LH exchange transfusion. Within-layer flow distributions showed lower heterogeneity with (n = 8) than without (n = 8) LH transfusion. No extravasation of hemoglobin was confirmed by 3,3-diaminobenzidin staining (n = 2). Carotid flow increased by 68% due to LH transfusion, whereas arterial pressure and heart rate remained unchanged. On the other hand, cross-circulated rat hearts (n = 7) were used to evaluate the effects of 50% blood-LH exchange on coronary flow and tone preservation under 300-beats/min pacing and 100-mmHg perfusion pressure. Blood-LH exchange caused a 71% increase of coronary flow and 10% decrease of percent flow increase during hyperemia after 30-s flow interruption. Myocardial [O.sub.2] supply and consumption increased by 9% and 10%, respectively, whereas myocardial [O.sub.2] extraction remained unchanged. The large increases of in vivo carotid flow and coronary flow in cross-circulated hearts due to LH coperfusion could be explained by the reduction of apparent flow viscosity. These results suggest that under LH coperfusion, the microheterogeneity of myocardial flows decreases with increased coronary flow while fairly preserving coronary tone and cardiac function. blood rheology; coronary tone; myocardial flow heterogeneity; cross-circulated rat heart

Byline: Jorn Adolphs (1), Diego K. Schmidt (1), Ines Korsukewitz (1), Britta Kamin (1), Helmut Habazettl (2,3), Michael Schafer (1), Martin Welte (4) Keywords: Animal model; Sympathetic blockade; Sepsis; Intravital microscopy; Blood flow; Mucosa Abstract: Objective To investigate whether sympathetic blockade by means of thoracic epidural anaesthesia (TEA) increases intestinal perfusion during normotensive endotoxaemia. Design A prospective, randomised and controlled animal study. Setting Animal laboratory in a university hospital. Subjects Sprague-Dawley male rats. Interventions The rats were anaesthetised with urethane and ketamine, mechanically ventilated and haemodynamically monitored. Lidocaine or saline were infused continuously via thoracic epidural catheters followed by a continuous intravenous infusion of Escherichia coli lipopolysaccharide (1.5 mg/kg per h). Densities of perfused and non-perfused capillaries (i.e., with and without erythrocyte perfusion, respectively) as well as erythrocyte velocity in both the mucosa and the muscularis of the terminal ileum were determined using intravital microscopy. Measurements and results Measurements were performed at baseline, after 30 min of epidural infusion as well as after 60 and 120 min of lipopolysaccharide infusion. In animals receiving TEA, mean arterial pressure and heart rate were significantly reduced throughout the experiment. In the muscularis the endotoxaemia-induced increase in non-perfused capillaries was absent with epidural lidocaine (0 [0/0] versus 39 [36/137] cm.sup.-1, median [25.sup.th/75.sup.th percentile]), whereas in the mucosa perfused capillary density declined to a greater extent than in controls (-47 [-53/-23]%) versus -19 [-34/+10]%, p Conclusions Microvascular perfusion data during endotoxaemia show a redistribution of blood flow towards the mucosa. TEA seems to impede this redistribution resulting in improved muscularis and worsened mucosal microvascular perfusion. Author Affiliation: (1) Department of Anaesthesiology and Critical Care Medicine, Campus Benjamin Franklin, Charite--Universitatsmedizin Berlin, Hindenburgdamm 30, 12200, Berlin, Germany (2) Department of Physiology, Campus Benjamin Franklin, Charite--Universitatsmedizin Berlin, Arnimallee 22, 14095, Berlin, Germany (3) Department of Anaesthesiology, Deutsches Herzzentrum Berlin, Augustenburger Platz 1, 13353, Berlin, Germany (4) Department of Anaesthesiology and Intensive Care Medicine, Klinikum Darmstadt, Grafenstrasse 9, 64283, Darmstadt, Germany Article History: Registration Date: 05/08/2004 Received Date: 04/03/2004 Accepted Date: 30/07/2004 Online Date: 26/08/2004

An on-line in vitro perfusion technique is described that allows the continuous quantification of cellular glucose metabolism in vitro. Using biosensor technology, we measure glucose and lactate metabolism at a minute-to-minute time resolution for periods up to several days. The application of our perfusion--detection technique for in vitro monitoring is demonstrated in a wide variety of cells, including primary neuronal and astroglia cultures, yeast cells, and human lymphocytes. The method shows that variations in oxygen delivery or exposure to a noncompetitive pseudosubstrate (here 2-deoxyglucose) affects normal glucose metabolism. The innovative advantage of the present system is that, in contrast to other devices including a recently described system, metabolism per cell can be quantified. The potential of in vitro on-line monitoring is discussed for application in studying normal and abnormal metabolism, toxic and nontoxic drug effects, and human tissue biopsies.