Henry A. Sloviter

Oxygen-sensitive 19F NMR imaging of the vascular system in vivo

The fluorine nuclear magnetic resonance spin-lattice relaxation rate (1/T1) of the perfluorochemical blood substitute perfluorotripropylamine (FTPA) is very sensitive to oxygen tension. This presents the possibility of measuring blood oxygen tension by 19F MR imaging. We obtained oxygen-sensitive 19F NMR images of the circulatory system of rats infused with emulsified FTPA. Blood oxygenation was assessed under conditions of both air- and 100% O2-breathing. T1 relaxation times were derived from MR images using a partial saturation pulse sequence. The T1 times were compared with a phantom calibration curve to calculate average blood pO2 values in the lung, liver, and spleen. The results showed marked, organ-specific increases in blood oxygen tension when the rat breathed 100% O2 instead of air.

In vivo measurements of vascular oxygen tension in tumors using MRI of a fluorinated blood substitute.

The authors measured the level of blood oxygenation in vivo in a series of rats with implanted mammary adenocarcinoma. The technique used was 19F magnetic resonance imaging of a perfluorochemical blood substitute. The method is based on the effect of oxygen on the T1 relaxation time of the fluorochemical and allows the determination of mean vascular PO2 independent of the blood volume in the tissue. The PO2 levels in the liver, lung, and spleen also were determined and were consistent with previously reported results. When the rats breathed air, the tumor PO2 levels were somewhat lower than in the other organs and were in a range typical of venous blood. When the rat was given 100% oxygen to breathe, the tumor PO2 levels increased far less than the PO2 levels of the other organs. This may indicate a greatly diminished blood flow to this particular tumor.

In Vivo 19F NMR Imaging of the Cardiovascular System

A technique is described that permits the 19F nuclear magnetic resonance (NMR) imaging of the vascular system in animals that have been infused with certain perfluorocarbon blood substitutes. The essence of the technique is the selection for imaging of a narrow group of spectral lines from the fluorocarbon using a combination of selective excitation and selective spin echo. For perfluorotributylamine (FTBA), this uses 569f of the available fluorine signal. Both slice and whole body projection images were obtained. The method was studied on an experimental NMR imaging system based on a 1.4 T. 31 cm diameter magnet. Phantom tests showed that misregistration artifacts, due to the imaging of unwanted spectral lines, were negligible. The spatial resolution obtained in a scan time of 8.5 min was ∼l mm. The technique was tested with living rats in which 56% of the blood volume was replaced with an emulsion of FTBA. Short echo times, less than 15 ms, were essential to avoid losing signal from flow effects in the larger vessels. Structures identified included the heart, liver, spleen, lungs, kidneys, and major veins. A diffuse fluorine signal seen in most tissues is indicative of tissue perfusion. The problems and possibilities of potential clinical applications are discussed.

Magnetic Resonance Imaging of Fluorine in Rats Infused with Artificial Blood

An MRI pulse sequence has been developed that enables the visualization of a perfluorocarbon (PFC) emulsion in the vascular system of rats. Images were made at 0.12T on a clinical imaging system using a small receiver coil, at intervals of approximately 2 hours, two days, two weeks, and two months after replacement of 50% of total blood volume. The most successful technique produced PA projections of the entire torso for both the fluorine and proton components. Direct comparison allowed identification of PFC in heart, lung, liver, spleen, and large vessels both in vivo and postmortem. Potential clinical applications to vascular imaging are discussed.

Fluorinated blood substitute retention in the rat measured by fluorine-19 magnetic resonance imaging.

RATIONALE AND OBJECTIVES Emulsions of perfluorocarbons (PFCs) have been tested as blood substitutes. However, evidence exists that there is long-term retention of some PFCs by the organs of the reticuloendothelial system (RES). The authors investigate organ retention of the blood substitute component, perfluorotripropylamine (FTPA), using fluorine-19 (19F) magnetic resonance imaging (MRI). METHODS Various dosages of an emulsion of FTPA were administered to five rats. At intervals up to 86 weeks after infusion, 19F MRI was used to measure the amount of FTPA in liver and spleen. The data were fit to both linear and exponential elimination models, and organ retention half-lives were calculated. RESULTS The exponential half-lives for combined liver and spleen FTPA ranged from 110 to 190 days. Linear half-lives ranged from 175 to 300 days. CONCLUSIONS FTPA retained by the liver and spleen may be quantified by 19F MRI: The half-lives that were measured are longer than those reported previously for FTPA.

Effects of intravenous emulsified perfluorochemicals on hepatic cytochrome P-450.

Intravenous infusion of emulsified perfluorodecalin in rats caused a large increase in hepatic cytochrome P-450 concentration which persisted for many weeks. In contrast, hepatic cytochrome P-450 concentration was not changed significantly after infusion of perfluorotributylamine, but subsequent administration of phenobarbital caused the usual increase of cytochrome P-450. The cytochrome P-450 activity for demethylation of benzphetamine was decreased slightly after perfluorodecalin but was unchanged after perfluorotributylamine. The difference in the effects of these perfluorochemicals on hepatic cytochrome P-450 may be related to the difference in the time these compounds are retained in the liver.

METABOLISM OF ISOLATED RAT BRAIN PERFUSED WITH GLUCOSE OR MANNOSE AS SUBSTRATE

Abstract— After isolated rat brain preparations were perfused with fluid containing either mannose or glucose as metabolic substrate, extracts from the rapidly frozen cerebral cortex were prepared and analysed. Brains perfused with mannose contained somewhat lower levels of glucose‐6‐phosphate and fructose diphosphate than those perfused with glucose but the contents of other glycolytic intermediates were quite similar in both groups. The level of mannose‐6‐phosphate was high in brains perfused with either glucose or mannose, but higher in the latter. In both cases, the ratio of mannose‐6‐phosphate to fructose‐6‐phosphate was very high, suggesting that phosphomannose isomerase (EC 5.3.1.8) may be important in the regulation of glycolysis. The levels of adenine nucleotides and creatine phosphate and the redox ratios were not significantly different with mannose as substrate than with glucose. The contents of free amino acids in brains perfused with mannose did not differ significantly from those in brains perfused with glucose. Our results show that mannose is a satisfactory substrate for the brain under these experimental conditions since it maintains the energy reserves and oxidative status of the cerebral tissue and does not alter the levels of amino acids.

Intestinal ischemia: Treatment by peritoneal lavage with oxygenated perfluorochemical

Though the delivery of elemental oxygen to tissues ravaged by anaerobic infection may be useful, little data exists that suggests that such therapy may benefit ischemic tissue. We report the development of a model to test the question that peritoneal lavage with an oxygen containing solution may favorably influence occlusive intestinal ischemia. Adult Sprague-Dawley rats with Nembutal (sodium pentobarbital) anesthesia underwent midline laparotomy; a microvascular clamp was applied to the superior mesenteric artery (SMA); and an inflow and outflow lavage catheter was placed. Treatment groups included control rats undergoing SMA occlusion only without lavage, rats lavaged with albumin during SMA occlusion (medium control), and rats lavaged during SMA occlusion with oxygenated perfluorochemical FC-47 emulsified in albumin (O2-FC-47). The increase in serum L-lactate following occlusion was used as an index of intestinal injury whether the perfusate was maintained at room temperature (28 degrees C) or body temperature (37 degrees C). Beginning with time O, which corresponded to the time of unclamping, subsequent samples were collected at 15, 30, and 60 minutes after a 30-minute SMA occlusion. Sequential lactates in 13 control rats were 4.18, 4.10, 3.88, and 4.52 mmol/L. Albumin lavaged animals had values at 28 degrees C of 2.23, 1.35, 1.8, and 2.44 mmol/L and values at 37 degrees C of 2.22, 1.40, 2.07, and 3.21 mmol/L, respectively. With O2-FC-47 lavage the respective lactates were 1.89, 1.09, 1.32, and 1.44 mmol/L at 28 degrees C and 2.14, 2.19, 2.50, and 2.1 mmol/L at 37 degrees C.(ABSTRACT TRUNCATED AT 250 WORDS)

Enzymic method for measuring dissolved oxygen in nonaqueous materials

Abstract A method based on the glucose oxidase reaction has been developed for measuring the amount of oxygen dissolved in aqueous or nonaqueous solvents. Samples containing 0.2 to 0.7 μmoles of oxygen react with an excess of glucose in the presence of glucose oxidase and the extent of reaction is determined by measuring the amount of glucose consumed. The method is calibrated by using, as standard, water which has been equilibrated with air at 20°. The amount of glucose consumed is a linear function of the amount of oxygen present. The molar ratio of glucose to oxygen consumed varied between 1.5 and 1.8. The limiting value for this ratio is 2.0 when catalase (a contaminant of commercial glucose oxidase) is present. Results of the analysis of suspensions of a dispersed fluorochemical showed a linear relationship between the amount of fluorochemical added and glucose consumed. The oxygen content of the dispersed fluorochemical equilibrated with oxygen was very close to 5 times that of the same material when equilibrated with air.

The biosynthesis of glycerides and glycerophosphatides by rabbit reticulocytes

Abstract 1. 1. When rabbit reticulocytes were incubated with [1- 14 C]glycerol, radioactivity was incorporated into glycerides and glycerophosphatides but no radioactivity was present in their fatty acid moieties or in cholesterol. 2. 2. Lecithin and ethanolamine phosphatide together contained about 70% and the neutral lipids about 20% of the total radioactivity. The triglyceride, which comprised less than 2% of the lipids, had the highest specific activity of all the lipids. 3. 3. Experiments with other radioactive precursors of the phosphatides gave results which indicate that the minor phosphatides are metabolically much less active than lecithin and that the formation of lecithin from serine phosphatide or ethanol-amine phosphatide is quantitatively unimportant in these cells. 4. 4. Incubation of rabbit reticulocytes with [2- 3 H]inositol resulted in the formation of radioactive phosphoinositides. Most of this radioactivity was present in a monophosphoinositide.