Psychoactive properties of amantadine.
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Biomedical subjects
J Wilcox
Publications and source records attributed to J Wilcox.
Urographic excretion studies with nonionic contrast agents. Iopamidol vs. iothalamate.
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Animals↗
Pre-operative nutritional support in children with end-stage liver disease accepted for liver transplantation: an approach to management.
Pre-operative nutritional support was studied in 28 children with end-stage liver disease awaiting orthotopic liver transplantation. Nasogastric supplemental administration of a standard semi-elemental enteral nutritional formula was compared with a similar formula enriched with branched chain amino acids, and with a group receiving oral nutrition only. The duration of treatment in all groups was similar (mean 90 days). Energy intakes in the supplemented groups were 120-150% of recommended daily intakes (RDI), whereas ad libitum intakes in the oral group ranged 58-100% RDI. A significant improvement in mean Z-score for body weight (denoting catch-up) was noted only in those children who received nasogastric supplements enriched with branched-chain amino acids. The standard enterally-fed group maintained their body weight and Z-scores did not change significantly. In contrast, body weight Z-scores in those fed orally declined significantly. Nutritional supportive therapy of malnourished children with end-stage liver disease can minimize or improve nutritional status in children awaiting liver transplantation. The use of nutritional formulae rich in branched-chain amino acids may have nutritional advantages in children with chronic liver disease which require further study and evaluation.
Amino Acids, Branched-Chain↗
The effect of contrast medium viscosity on the blood-brain barrier after intracarotid injection in the rabbit.
This study was undertaken to investigate the role of contrast medium viscosity in blood-brain barrier disruption after carotid angiography. Test solutions were injected into the carotid arteries of rabbits, and the degree of disruption was assessed by using 99mTc-pertechnetate and Evans blue as quantitative and qualitative markers, respectively. The seven test solutions consisted of basic solutions of physiological saline, iopromide, or methylglucamine iothalamate plus solutions derived from these by the addition of sufficient gelatin to augment their viscosities considerably. The solutions were injected over a 30-sec period, resulting in doses that varied inversely with viscosity. One of the high-viscosity solutions was also injected as a fixed dose, equal to the mean injection volume of its low-viscosity counterpart, without regard to the time used. Statistical comparison between the effects of the solutions showed that, under the conditions of the study, contrast medium viscosity, either by itself or as a consequence of its association with hyperosmolality, has no significant effect on the blood-brain barrier. However, under conditions of constant injection volume, higher viscosity solutions may require increased injection times, and this may lead to increased disruption of the blood-brain barrier.
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A comparison of blood-brain barrier disruption by intracarotid iohexol and iodixanol in the rabbit.
A rabbit model was used to compare the effect on the blood-brain barrier of the intracarotid injection of two new contrast media: iohexol, a nonionic monomer, and iodixanol, a nonionic dimer. It was hypothesized that the low osmolality of iodixanol (272 mOsm/kg at 300 mgl/ml) would cause less disruption of the blood-brain barrier than the relatively higher osmolality of iohexol (690 mOsm/kg at 300 mgl/ml). The degree of blood-brain barrier disruption was assessed qualitatively, by observing the degree of cortical staining with Evans' Blue dye, and quantitatively, by calculating the difference in uptake of 99mTc-pertechnetate between injected and noninjected hemispheres. Statistical analysis of the results showed that both iodixanol and iohexol had a significantly greater effect on blood-brain barrier disruption than did isotonic saline (0.005 greater than p greater than .001), but that the effect of iodixanol was not significantly different from that of iohexol with respect to either Evans' Blue staining (p greater than .05) or pertechnetate uptake (.75 less than p less than .90). Thus, the low-osmolality iodixanol has no significant advantage over iohexol in terms of blood-brain barrier disruption after experimental carotid angiography.
Animals↗
Effect of intravenous contrast material on the integrity of the blood-brain barrier: experimental study.
Increasingly large doses of contrast medium have been advocated for enhanced computed tomography. It is assumed that such large intravenous doses, which increase the osmolality of the blood, do not affect the blood-brain barrier in the same way as intracarotid injections of the same solutions. Using a qualitative marker, Evans blue dye, and a quantitative marker, 99mTc-pertechnetate, a study was performed in rabbits to assess the effect of intravenous sodium iothalamate (Conray-420) at a dose of 8 ml/kg on the integrity of the blood-brain barrier. No qualitative or quantitative evidence of disruption of the blood-brain barrier was demonstrated. Since histologic examination was not done, morphologic changes cannot be excluded.
Animals↗
Comparison of blood-brain barrier disruption by intracarotid iopamidol and methylglucamine iothalamate.
Using a canine model, the effect of intracarotid injections of the ionic contrast medium methylglucamine iothalamate was compared with that of the nonionic contrast medium iopamidol of similar iodine concentration (280 mg 1/ml). The degree and distribution of blood-brain barrier disruption was assessed using Evans blue stain as a visual marker and by contrast enhancement measured by a computed tomographic (CT) scanner. In all studies with methylglucamine iothalamate, Evans blue staining was demonstrated, and CT enhancement demonstrated a significant mean difference (p less than 0.01) between the control and injected hemispheres. The absence of blood-brain barrier disruption with iopamidol is probably related to its lower osmolality (570 mosmol/kg) compared with methylglucamine iothalamate (1,424 mosmol/kg) and the absence of any cation.
Animals↗
Brain parenchyma penetration by intrathecal nonionic iopamidol.
Iopamidol, a nonionic, water-soluble contrast medium, has been recently recommended for myelography. As with other such media, the extent of parenchymal penetration is of interest in relation to the genesis of clinical complications. In this study the degree and depth of brain penetration of intrathecal iopamidol, using an iodine concentration of 280 mg l/ml, were compared at 15 and 60 min in adult greyhound dogs using coronal computed tomographic scanning of the brain after removal. A significant but patchy penetration corresponding to the cortical sulci was demonstrated at 15 min, while by 60 min there had been a further increase in the distribution and concentration of the contrast medium. Comparing the present study with a previous series using metrizamide and methylglucamine iothalamate at a similar iodine concentration (280 mg l/ml), no significant difference in the depth or degree of penetration at 60 min was found between the three contrast media, indicating a similar rate of diffusion across the cerebrospinal fluid/brain interface. Therefore, any difference in neurotoxicity is not explained by a reduced concentration of contrast medium due to variation in the rate of diffusion across this interface.
Animals↗
Comparison and evaluation of osmotic blood-brain barrier disruption following intracarotid mannitol and methylglucamine iothalamate.
The effect of intracarotid injections of methylglucamine iothalamate has been compared with that of mannitol solution of similar osmotic strength. The degree and distribution of blood-brain barrier disruption was assessed using Evans' Blue dye as a visual marker and by contrast enhancement measured by computer tomography (CT) scanner. Evans' Blue staining was found to match CT enhancement closely. It was also found that methylglucamine iothalamate injections resulted in significantly greater blood-brain barrier permeability. The relevance of these findings to chemotherapy of brain tumours is discussed briefly.
Animals↗
Brain parenchyma penetration by intrathecal ionic and nonionic contrast media.
Metrizamide, a nonionic water-soluble contrast medium, has been shown to penetrate normal brain when injected intrathecally. Recently it was suggested that the complications following intrathecal metrizamide are directly related to the cerebral concentration reached. Metrizamide, both in experimental animals and clinically, is regarded as less neurotoxic than equivalent iodine concentrations of ionic contrast media. In this study the degree and depth of brain penetration of intrathecal metrizamide and methylglucamine iothalamate (Conray 280), using a similar iodine concentration (280 mg l/ml), was compared at 1 hr in adult greyhound dogs. The depth of penetration and concentration reached in the cortical gray matter was determined by coronal computed tomographic scanning of the brain after removal. No significant difference was found between the two contrast media, suggesting that the rate of diffusion across the cerebrospinal fluid-brain interface is similar and that the difference in neurotoxicity is not explained by a reduced concentration of contrast medium in the case of nonionic metrizamide, when compared with ionic methylglucamine iothalamate. Using Evans blue as a qualitative marker, no evidence of gross blood-brain disruption was demonstrated in the area of maximum penetration with either contrast medium.
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