The measurement of colonic mucosal-submucosal blood flow in man

Pumpless, unidirectional microphysiological system for testing metabolism-dependent chemotherapeutic toxicity

Drug development is often hindered by the failure of preclinical models to accurately assess and predict the efficacy and safety of drug candidates. Body-on-a-chip (BOC) microfluidic devices, a subset of microphysiological systems (MPS), are being created to better predict human responses to drugs. Each BOC is designed with separate organ chambers interconnected with microfluidic channels mimicking blood recirculation. Here, we describe the design of the first pumpless, unidirectional, multiorgan system and apply this design concept for testing anticancer drug treatments. HCT-116 colon cancer spheroids, HepG2/C3A hepatocytes, and HL-60 promyeloblasts were embedded in collagen hydrogels and cultured within compartments representing "colon tumor", "liver," and "bone marrow" tissue, respectively. Operating on a pumpless platform, the microfluidic channel design provides unidirectional perfusion at physiologically realistic ratios to multiple channels simultaneously. The metabolism-dependent toxic effect of Tegafur, an oral prodrug of 5-fluorouracil, combined with uracil was examined in each cell type. Tegafur-uracil treatment induced substantial cell death in HCT-116 cells and this cytotoxic response was reduced for multicellular spheroids compared to single cells, likely due to diffusion-limited drug penetration. Additionally, off-target toxicity was detected by HL-60 cells, which demonstrate that such systems can provide useful information on dose-limiting side effects. Collectively, this microscale cell culture analog is a valuable physiologically-based pharmacokinetic drug screening platform that may be used to support cancer drug development.

Mucosal/submucosal blood flow in the small intestine in pigs determined by local washout of 133Xe and microsphere techniques

In 11 anaesthetized pigs a laparotomy was performed and the mucosal and submucosal blood flow rate in the small intestine of the pig was determined by a local application of 133Xe and by 6.5-microns radioactive microspheres. The 133Xe washout plotted in a semilogarithmic diagram showed a multiexponential configuration. As localization studies of 133Xe in the intestinal mucosa showed a constant high concentration of 133Xe in the luminal part of the mucosa due to shunting by diffusion, the initial slope of the 133Xe washout was used for blood flow determination in the mucosa/submucosa. There was a good relationship between blood flow determined by the two techniques. The correlation coefficient, R, between the two techniques was 0.89.

Non-invasive endoscopic technique to assess gastrointestinal perfusion

Changes in mucosal blood flow may occur in many gastrointestinal disorders, but assessment is impossible without a non-invasive in vivo technique. We have compared endoscopic laser Doppler (LD) with oxygen electrode (OE) measurements in a dog isolated colon preparation, using variable perfusion measured with an electromagnetic flow probe. At maximum flow, LD measurements were made at three sites to compare mucosal with serosal readings. Flow rate was varied (1-38 ml/min) and measurements of microcirculatory flux obtained using LD, and of oxygen tension using a serosal OE. A progressive trend towards increasing flux was demonstrated from caecum to rectum-serosa: 46.8 +/- 18.7 V (caecum), 52.6 +/- 17.9 V (mid-colon) and 61.3 +/- 17.6 V (rectum). A parallel trend was observed in mucosal values: 41.1 +/- 18.2 V (caecum), 45.7 +/- 15.2 V (mid-colon) and 54.1 +/- 15.1 V (rectum). At all sites, serosal and mucosal values were not significantly different (Student's t test). LD serosal values correlated significantly with EM flow (r = 0.544, 0.01 greater than P greater than 0.001). A similar linear correlation was found between OE and EM flow (r = 0.65, P less than 0.001). Oxygen tension measurements varied as expected with microcirculatory flux (r = 0.441, 0.02 greater than P greater than 0.01). Endoscopic LD assessment of colonic microcirculation accurately reflects changes in blood flow.

Effect of a somatostatin analogue, SMS 201-995, on 133Xe clearance from colonic mucosa in unanesthetized man

The effect of intravenous bolus injection of the somatostatin analogue SMS 201-995 on mucosal and submucosal blood flow was studied with the local 133Xe clearance technique in eight subjects. Mucosal and submucosal blood flow decreased by 33% after injection of SMS 201-995. These observations suggest that SMS 201-995, like somatostatin, inhibits splanchnic blood flow.

Effect of somatostatin on 133Xe clearance from colonic mucosa before and after local nervous blockade in unanaesthetized man

The effect of intravenous somatostatin bolus on mucosal and submucosal blood flow in six patients with colostomies was studied with the local 133Xe clearance technique. Mucosal and submucosal blood flow decreased by 28% after somatostatin injection. After induction of local nervous blockade by infiltrating the labelled area of the mucosal membrane with lidocaine the reduction in blood flow caused by somatostatin was abolished. These observations suggest that the vasoconstrictor effect of somatostatin is mediated by neurogenic mechanisms.

Immunological control of drug absorption from the gastrointestinal tract: the mechanism whereby intestinal anaphylaxis interferes with the intestinal absorption of bromthymol blue in the rat

Rats were immunized intraperitoneally with ovalbumin and the disappearance of bromthymol blue (BTB) from the intestinal lumen, its accumulation in the tissue, and its net absorption were examined by means of an in-situ recirculation technique during local anaphylaxis. The disappearance of BTB from the intestinal lumen and its net absorption were significantly reduced, but there was no significant effect on its accumulation in the tissue. The pH value of the luminal solution and the perfusate volume were not influenced by intraluminal challenge with the antigen in ovalbumin-immunized rats. In addition, no significant effect was observed on intestinal permeability to BTB in the in-vitro everted sac technique. The intestinal blood flow, measured by a hydrogen clearance method, was not reduced significantly by the intraluminal exposure to antigen. There was enhanced Evans Blue leakage and mucus release in the perfusate after intraluminal challenge with ovalbumin in ovalbumin-immunized rats, but not in non-immunized rats. A significant increase of BTB binding with macromolecular substances in the perfusate was observed during the local anaphylaxis. These findings suggest that the decreased absorption of BTB is due to the interaction with the macromolecular substances in the perfusate during local anaphylaxis.

Changes in intestinal blood flow during the development of chronic large bowel obstruction

The effect of chronic progressive distal large bowel obstruction on intestinal blood flow was studied in 12 mini-pigs. Blood flow was measured by the techniques of xenon133 clearance and intracardiac injections of radiolabelled microspheres. Intestinal blood flow was increased in the left colon and ileum but decreased in the caecum. Blood was shunted from the mucosa to the muscle layers. The results suggest that primary anastomosis of the obstructed left colon is not contraindicated by haemodynamic considerations.

The relationship between temperature isotherms and skin blood flow in the ischemic limb

This study was conducted in order to establish a relationship between thermographically defined levels of viability in the ischemic limb and a measurement of skin blood flow. Color thermograms (10 colors, 0.6 degree C apart) defined the temperature gradient and skin blood flow was measured, using the radioactive clearance method in three discrete isotherms set 1.8 degrees C apart. The differences in skin blood flow measured in the three separate isotherms were significant (P less than 0.001). The results of this study support previously unqualified assertions that thermographic temperature gradients along an ischemic limb are indicative of local microcirculatory status. The potential of the thermographic method for demarcating viable and nonviable skin flaps at the chosen site of amputation is confirmed.

Sodium current in single rat heart muscle cells

1. Rapid inward Na current (INa) was studied in isolated cells from rat ventricular myocardium by a double-suction-pipette voltage clamp technique. All experiments were carried out at 20-22 degrees C. 2. INa elicited by single depolarizing voltage steps from a holding potential, VH, of -80 mV had a threshold between -70 and -60 mV and was maximal at -30 to -20 mV. Peak currents in Krebs-Ringer solution containing 145 mM Na were of the order 0.9-1.8 mA cm-2, assuming an average cell surface area of 8000 square micrometers. 3. The reversal potential for INa was predicted by the Nernst equation for external Na in the range 1.45-145 mM with 16 mM-Na solution perfusing the interior of the cell. 4. Instantaneous I-V plots were linear for potentials of -100 to + 10 mV. Maximum Na conductance (-gNa) was calculated to be 25 mS cm-2 in 145 mM-Na solutions and gNa was constant for potentials positive to -10 mV. 5. INa activated with a time constant of 0.7 msec at -55 mV, decreasing to 100 microsec on depolarizations positive to + 10 mV. 6. Two time constants (tau h1, tau h2) were required to describe INa inactivation during a maintained depolarization, with tau h2 three to four times as long as tau h1. tau h1 was about 2 msec at -50 mV, decreasing to 0.9 msec at -10 mV. 7. The time course for recovery of INa from inactivation also exhibited two time constants (tau r1, tau r2), with the longer tau r2 having a maximum value of the order 100 msec in the potential range -60 to -80 mV. 8. INa in isolated rat cardiac cells has a low sensitivity to tetrodotoxin, requiring a concentration of 30 micrometers for complete blockade.

Colonic mucosal-submucosal blood flow and the incidence of faecal fistula formation following colostomy closure

Fistula formation following closure of a colostomy occurs most frequently when closure is carried out within the first few weeks of construction and may be related to an impaired local microcirculation. Using a recently described method for measuring colonic mucosal-submucosal blood flow, the variations in local flow which occur during the first month after colostomy construction were determined in 8 patients. Mean blood flow increased from 6.9 +/- 1.8 ml min-1 100 g-1 (s.d.) at 7 days to 31.1 +/- 12.5 ml min-1 100 g-1 (s.d.) at 28 days. In a further 40 consecutive patients undergoing colostomy closure, blood flow measurements were made before operation. Eight patients developed a faecal fistula, and in 5 of these patients mucosal-submucosal blood flow was found to be less than 15 ml min-1 100 g-1. In every successful colostomy closure blood flow was greater than 15 ml min-1 100 g-1. This study provides evidence that a subnormal blood flow is one of the factors associated with fistula formation following the operation of colostomy closure.

Changes in human colonic mucosal-submucosal blood flow after body surface cooling

Mucosal-submucosal blood flow in the human colostomy was measured by a radioisotopic washout technique. Changes in blood flow were recorded in 10 subjects after peripheral vasoconstriction evoked by surface cooling of the body. Accompanying the vasoconstriction was a rise in mucosal-submucosal blood flow of approximately 40%. An interpretation of the blood flow changes and the associated alterations in mean arterial blood pressure provide evidence for vasomotor and local regulatory control in the colostomy microcirculation. We believe, therefore that the colostomy is a suitable preparation for studying the human colonic microcirculation.