Diffusion weighted imaging and magnetic resonance spectroscopy in a low flow ischaemia model due to endothelin induced vasospasm.

The aim of this MR study was to determine if vasospasm induced by application of endothelin-1 (ET-1) in the rat brain would model the abnormalities attributed to vasospasm described in patients with subarachnoid haemorrhage (SAH) with reversible neurological deficits. Following application of ET-1 in concentrations of 10(-4) M or 10(-6) M to the middle cerebral artery, there was an immediate drop in pH, an increase in the inorganic phosphate (P(i)) to phosphocreatine (PCr) ratio and elevated lactate. There was gradual recovery to control in the 10(-6) M group, but in the 10(-4) M group there was a loss of approximately 10% in the absolute signal intensities of PCr and adenosine triphosphate (ATP). In a second similarly treated group of animals, the area of the hemisphere with a low apparent diffusion coefficient (ADC) was 27 +/- 6% at 30 min and remained at about 20-21% at 90 min and beyond. Together these data suggest that the regions with persistently low ADC were metabolically compromised, with incomplete recovery of PCr and ATP, and represent irreversibly damaged tissue. This raises the possibility that MR spectroscopy and imaging could be a sensitive indicator of tissue viability. This is a potentially useful model of low flow as seen in clinical vasospasm following SAH.

31P magnetic resonance spectroscopy as a predictor of efficacy in photodynamic therapy using differently charged zinc phthalocyanines.

Photodynamic therapy (PDT) is a developing approach to the treatment of solid tumours which requires the combined action of light and a photosensitizing drug in the presence of adequate levels of molecular oxygen. We have developed a novel series of photosensitizers based on zinc phthalocyanine which are water-soluble and contain neutral (TDEPC), positive (PPC) and negative (TCPC) side-chains. The PDT effects of these sensitizers have been studied in a mouse model bearing the RIF-1 murine fibrosarcoma line studying tumour regrowth delay, phosphate metabolism by magnetic resonance spectroscopy (MRS) and blood flow, using D2O uptake and MRS. The two main aims of the study were to determine if MRS measurements made at the time of PDT treatment could potentially be predictive of ultimate PDT efficacy and to assess the effects of sensitizer charge on PDT in this model. It was clearly demonstrated that there is a relationship between MRS measurements during and immediately following PDT and the ultimate effect on the tumour. For all three drugs, tumour regrowth delay was greater with a 1-h time interval between drug and light administration than with a 24-h interval. In both cases, the order of tumour regrowth delay was PPC > TDEPC = TCPC (though the data at 24 h were not statistically significant). Correspondingly, there were greater effects on phosphate metabolism (measured at the time of PDT or soon after) for the 1-h than for the 24-h time interval. Again effects were greatest with the cationic PPC, with the sequence being PPC > TDEPC > TCPC. A parallel sequence was observed for the blood flow effects, demonstrating that reduction in blood flow is an important factor in PDT with these sensitizers.

The coming of the electronic age to the Cambridge Physiological Laboratory: E.D. Adrian's valve amplifier in 1921.

E.D. Adrian, F.R.S. (1889-1975) was one of Britain's most distinguished neurophysiologists, who, during a long and productive lifetime, achieved most honours and distinctions available to a scientific man. These included the 1932 Nobel Prize for Physiology or Medicine, shared with Sir Charles Sherrington, F.R.S., the Order of Merit (1942), and Presidency of the Royal Society (1950-55). His interest in the nervous system started at the beginning of his undergraduate career, much influenced by his Director of Studies, Keith Lucas, F.R.S. (1879-1916). Lucas, a skilled and imaginative neurophysiologist, was particularly renowned for his technical ability to design and build new equipment. In turn, his pupil's work on recording and analysing the electrical impulses in nervous tissue was also facilitated by the development of appropriate, sensitive instrumentation. This paper will describe Adrian's first use of valve amplifiers to enlarge the extremely small electrical signals then obtainable in the physiological laboratory, a development that epitomized the beginning of the electronic revolution in life sciences' laboratories.

Combination of photodynamic therapy (PDT) and melphalan in experimental tumors.

PURPOSE: To investigate whether application of "early" photodynamic therapy (PDT) using a disulphonated aluminium phthallocyanine photosensitizer can potentiate the action of melphalan in experimental RIF-1 tumors in vivo. METHODS AND MATERIALS: Tumors were irradiated with laser light of wavelength 675 nm 60 min after treatment with the photosensitizer and 15 min after melphalan. Melphalan pharmacokinetics were measured using high performance liquid chromatography with optical detection. RESULTS: Melphalan and PDT when given alone, caused a significant delay in tumor growth. This was increased for the combined treatment. Pharmacokinetic analyses showed that levels of free, unreacted melphalan in freely circulating blood are unaffected by combined treatment. However, significant differences in tumor levels were observed between treatment with melphalan alone or in combination. Whereas in the former, melphalan is still present in tumors after 2 h, it was not detectable even at the earliest time of 15-23 min for the combined treatment. CONCLUSION: The antitumor effects were additive with no evidence of significant potentiation.

Magnetic resonance spectroscopic studies on 'real-time' changes in RIF-1 tumour metabolism and blood flow during and after photodynamic therapy.

Magnetic resonance spectroscopy (MRS) in situ was used to study changes in 31P metabolism occurring during and after treatment of murine RIF-1 tumours with photodynamic therapy (PDT). Tumours were irradiated using a fibreoptic light delivery system while the mice were in position within the magnet. Changes in 31P-MRS were observable during and immediately after treatments of several minutes' duration. Both the extent and duration of the increase in the Pi/total ratio were light dose dependent. The effect on the metabolism was also affected by the time interval (TL) between administering the photosensitiser disulphonated phthalocyanine, (A1S2Pc) and the light. With a dose of 50 J the increase in Pi/total was much faster when TL was 1 h than when TL was 24 h. This difference in rate probably reflects differences in the distribution of A1S2Pc within the tumour. Significant decreases in pH were only seen after a light dose of 50 J when TL was 1 h. Blood flow measurements using deuterium uptake were also carried out using MRS. These experiments showed that for a dose of 50 J the level of blood flow was reduced by approximately 90% of the control value within 10 min from the end of the 8 min light treatment. This occurred irrespective of the value of TL. The data indicate that it is possible to observe very early changes in 31P metabolism that can be attributed to direct cellular damage as opposed to the later changes indicative of overall tumour hypoxia caused by vascular damage.

The accuracy and reproducibility of measuring blood flow in murine tumours by the D2O uptake and clearance techniques.

The use of D2O as an NMR visible tracer to monitor murine tumour blood flow (TBF) by both the wash-in and wash-out methods has been investigated. The factors that influence the models used to fit the data and the error on the measurement of the clearance and uptake rates have been assessed. The study concentrates on the uptake method which allows TBF to be measured without the need to use anaesthetic. Also, administering the D2O remotely to the mouse means it can remain undisturbed, in the magnet bore, between control and post-treatment readings. The uptake method in KHT and RIF-1 transplanted murine tumours has been investigated in a series of control experiments and after modifying TBF by hydralazine (5 mg/kg) and photodynamic therapy. These studies showed that four uptake measurements could be made on the same mouse at 20 min intervals without affecting TBF, control values were the same for anaesthetized and unanaesthetized mice and the values obtained for RIF-1 tumours were marginally higher than those obtained for the KHT tumours. The decrease in TBF seen after modification was in good agreement with published data where TBF results were obtained by using D2O clearance, radioactive tracers or laser Doppler flowmetry.

Comparing the anti-tumor effect of several bioreductive drugs when used in combination with photodynamic therapy (PDT).

PURPOSE: To compare the effect on the RIF-1 murine sarcoma of nine bioreductive agents from five different classes when used in combination with either photodynamic therapy or clamping. METHODS AND MATERIALS: RIF-1 tumors implanted intradermally in C3H mice were treated with either 50J photodynamic therapy or with 120 min clamping in combination with either misonidazole, pimonidazole, metronidazole, nimorazole, RB6145, RSU1069, SR4233, mitomycin-C, or RB90740. The tumors were measured 3 times-per-week until reaching 4 x their initial treatment volume. RESULTS: RSU1069 produced the greatest anti-tumor activity in combination with both photodynamic therapy and clamping. RB6145 also substantially enhanced the effect of photodynamic therapy and clamping whereas misonidazole induced a smaller, but significant increase. Mitomycin-C had no effect under clamped conditions, but greatly increased the tumorcidal effect of photodynamic therapy. Mitomycin-C also induced an effect when given with light alone. None of the other agents showed any augmentation of the tumor cell killing induced by photodynamic therapy. CONCLUSION: Of the bioreductive agents studied RSU1069, RB6145 and mitomycin-C showed the greatest anti-tumor response in combination with photodynamic therapy.

Phosphorus metabolism during growth of lymphoma in mouse liver: a comparison of 31P magnetic resonance spectroscopy in vivo and in vitro.

Large phosphomonoester (PME) signals are detected in the phosphorus magnetic resonance spectra (31P MRS) of many neoplastic and rapidly dividing tissues. In addition, alterations in phosphodiester (PDE) signals are sometimes seen. The present study of a murine lymphoma growing in liver showed a positive correlation between the hepatic PME/PDE ratio measured in vivo by 31P MRS at 4.7 T and the degree of lymphomatous infiltration in the liver, quantified by histology. High-resolution 31P MRS of liver extracts at 9.7 T showed that the PME peak consists largely of phosphoethanolamine (PE) and to a lesser extent of phosphocholine (PC). The concentration of both PE and PC increased positively with lymphomatous infiltration of the liver. In vivo, the PDE peak contains signals from phospholipids (mostly phosphatidylethanolamine and phosphatidylcholine) and the phospholipid breakdown products glycerophosphoethanolamine (GPE) and glycerophosphocholine (GPC). Low levels of GPE and GPC were detected in the aqueous extracts of the control and infiltrated livers; their concentrations remained unchanged as the infiltration increased. The total concentration of phospholipids measured by 31P MRS of organic extracts decreased about 3-fold as the infiltration increased to 70%. Thus, our data showed that the increased PME/PDE ratio in vivo is due to both an increase in the PME metabolites and a decrease in the PDE metabolites. We propose that this ratio can be used as a non-invasive measure of the degree of lymphomatous infiltration in vivo.

Intraoperative hemodialysis during cardiopulmonary bypass in chronic renal failure.

This report describes the features and the course of a patient on maintenance hemodialysis in whom infective endocarditis of the aortic valve ensued. The subsequent development of intractable congestive heart failure necessitated aortic valve replacement. Use of intraoperative hemodialysis, facilitating the intraoperative and postoperative management of the patient, is described. Following valve replacement the patient did well with no evidence of congestive heart failure.