Orthostatic blood pressure control and ageing*

Reflex haemodynamic responses to orthostatic stress are attenuated with ageing, the extent of attenuation increasing with advancing age. In 15–20% of individuals aged >65 years, the attenuation may be so marked that there is an excessive fall of blood pressure (BP) on assumption of the upright posture, sufficient on occasions to cause symptomatic cerebral hypoperfusion - this is known as ‘ageing-related’ orthostatic hypotension (AOH), a major risk factor for morbidity and mortality. Comparison of the cardiovascular responses to a variety of physiological and pharmacological stresses in healthy young and elderly subjects and in those with AOH suggests that the predominant site of the ageing-related change in cardiovascular reflex function is in the central connections of the arterial baroreflex, affecting particularly the BP buffering response. There is no evidence for ageing-related impairment of the efferent limb of the baroreflex, i. e. there is no significant ageing change in sympathetic vasomotor function or cardiac drive. Ageing-related impairment of baroreflex function also does not appear to result from either attenuation of arterial compliance or the presence of systolic hypertension, despite the epidemiological association between systolic hypertension and AOH. Better understanding of this important problem has the potential to improve the health of all elderly people.     

Uroscopy in the 21st century: high-field NMR spectroscopy

From the experiments described, it can be seen that there are different research approaches that can be taken and these are summarized in Table 1. Whereas much scientific research is principally hypothesis led, there remains, nevertheless, an important place for exploratory research. High resolution NMR can measure, directly and simultaneously, a wide range of endogenous metabolites in biological fluids and has the unique capability of providing structural information on the metabolites detected. It has proved to be a powerful research tool with which to study inherited metabolic diseases, renal disease, drug metabolism, and toxicity, and can be used to monitor the effects of drug therapy. For instance, by using a library of experimental toxins one can map the metabolic profile of site-specific nephron injury. With this approach in man one could eventually take an unknown disease such as Balkan nephropathy and predict the initial site of tubular injury, the mode of injury and therefore the kind of toxin capable of producing that injury. NMR spectroscopic techniques are still advancing rapidly, with ever increasing sensitivity and sophistication of NMR pulse sequences to enhance structural elucidation in complex mixtures. Given the advances in directly coupled HPLC-NMR and even HPLC-NMR-mass spectroscopy it is likely that these technologies in conjunction with pattern recognition will make major contribution to our understanding of renal processes and provide new diagnostic insights in the 21st century.      

Fibrinogen adsorption and platelet adhesion at the surface of modified polypropylene glycol/polysiloxane networks

The protein film adsorbed at an artificial surface ultimately affects platelet adhesion and activation. This study examines the role of fibrinogen in platelet adhesion at the surface of crosslinked polypropylene glycol (PPG)/polyglycidoxy propyl methyl siloxane (PGPMS) networks which contain polyethylene glycol monomethyl ether (PEGME) chains. These crosslinked networks were produced by reacting the epoxy groups of PGPMS with the hydroxyl groups of the polyethers. PEGME chains were attached covalently to the network at only one end while PPG chains were attached at both ends. The incorporation of PEGME resulted in a substantial reduction in fibrinogen adsorption as compared to the model network (PPG + PGPMS only), but the expected concomitant decrease in platelet adhesion was not observed.     

A twin-family study of self-report symptoms of panic-phobia and somatization

Self-report symptoms of anxiety are widely used in mental health and social science research as an index of current psychiatric state. Previous twin studies have suggested that genetic factors account for a significant proportion of the variance in these symptoms. To replicate and extend these findings, we examined self-report symtoms of panic-phobia and somatization in the “Virginia 30,000” twin-family sample. Model fitting applied to 80 unique relationships in the twin-family pedigree produced the following major results: (i) genetic effects were significant for both symptom factors, accounting for between 25 and 49% of the total variance, with the exception of symptoms of panic-phobia in females, where they accounted for 15–16% of the variance; (ii) familial environmental effects were absent for symptoms of somatization, while for symptoms of panic-phobia they accounted for a very small proportion of variance in males (≤1.2%) and a modest proportion in females (6–17%) (iii) spousal correlations were present for both factors, ranging from +0.05 to +0.20; (iv) genetic factors which influenced symptoms were generally the same in males and females, although their effect was greater in males; (v) heritability estimates were lower in the population-based than in the volunteer sample; and (vi) when test-retest reliability was included in the model, results suggest that genetic factors account for at least half of the stable variance for all symptom factors, except panic-phobia in females. Our results support the validity of previous twin studies of self-report symptoms of anxiety and suggest that genetic factors significantly influence these symptoms but familial-environmental factors play little or no etiologic role.     

Distinction between normal and renal cell carcinoma kidney cortical biopsy samples using pattern recognition of (1)H magic angle spinning (MAS) NMR spectra

The technique of magic angle spinning (MAS) high resolution (1)H NMR spectroscopy applied to intact tissues provides excellent peak resolution and thus much biochemical information. The use of computer-based pattern recognition techniques to classify human renal cortex tissue samples as normal or tumour based on their (1)H MAS NMR spectra has been investigated. In this preliminary study of 22 paired control and tumour samples, exploratory data analysis using principal components based on NMR spectral intensities showed clear separation of the two classes. Furthermore, using the supervised method of linear discriminant analysis, based on individual data point intensities or on integrated spectral regions, it was possible to distinguish between the normal and tumour kidney cortex tissue with 100% accuracy, including a single example of a metastatic tumour from a primary lung carcinoma. A tumour sample from the collecting duct of the kidney showed a different NMR spectral profile, and pattern recognition indicated that this sample did not classify with the cortical tumours.     

Locating human quantitative trait loci: Guidelines for the selection of sibling pairs for genotyping

Simulation studies were conducted to assess the relative merits of different nonrandom sampling strategies for the selection of sibling pairs for genotyping in the attempt to locate individual loci (QTLs) contributing to variation in human quantitative traits. For a constant amount of variation contributed by a QTL (25% of the total) the frequencies and dominance relationships of a trait increasing allele were varied. Three strategies for selection of pairs for genotyping were based on the phenotypic values of the siblings: Concordant sib pairs (CSP) are pairs in which both individuals exceed a given threshold value; discordant sib pairs (DSP) are pairs in which one member exceeds a given upper threshold and the other is below a specified lower threshold; and most similar pairs (MSP) are pairs selected for falling below a specified percentile ranking of the within-pair mean square for the quantitative trait. Tests for linkage with markers at 1, 2, 5, 10, and 20 cM from each of the QTLs were conducted for each of the selected samples and compared with tests based on the regression, in the entire sample, of within pair variation on the proportion of alleles identical by descent (IBD) at each marker locus. Tests for the effect of the increasing allele at the QTL (candidate gene) were also conducted for the DSP pairs. No single nonrandom selection procedure yields as much as half the information realized in the total sample. However, a combined strategy which involves genotyping the 5% of MSP and DSP for the upper and lower quintiles of values of the quantitative trait (a further 3% of the sample approximately) yields lod scores which are usually more than 65% of the values realized for the entire sample. Tests comparing the proportion of increasing alleles in high- and low-scoring siblings from DSP samples are uniformly very powerful for detecting candidate loci. Even when it is not possible to measure the entire range of the phenotype with uniform precision, some attempt to differentiate among individuals in a common unaffected class of individuals can lead to considerable increase in power.     

Quantitative studies on the urinary metabolic fate of 2-chloro-4-trifluoromethylaniline in the rat using 19F-NMR spectroscopy and directly coupled HPLC-NMR-MS

1. The metabolism and urinary excretion of 2-chloro-4-trifluoromethylaniline has been studied in the rat using 19F-NMR spectroscopy and directly coupled HPLC-NMR-MS methods. The compound was dosed to three male Sprague-Dawley rats (50 mg kg(-1) i.p.) and urine collected over 0-8, 8-24 and 24-48 h post-dosing. 2. A total urinary recovery of 56.3+/-2.2% of the dose was achieved up to 48 h after dosing. The major metabolite in the urine was identified as 2-amino-3-chloro-5-trifluoromethylphenylsulphate accounting for a total of 33.5+/-2.2% of the dose. 3. Further metabolites detected and characterized included 2-chloro-4-trifluoromethylphenylhydroxylamine glucuronide (13.2+/-0.5% of the dose), 2-amino-3-chloro-5-trifluoromethylphenylglucuronide (3.8+/-0.4% of the dose) and 2-chloro-4-trifluoromethylaniline-N-glucuronide (3.6+/-0.1% of the dose). Several minor metabolites were also found and identified, including 2-chloro-4-trifluoromethylphenylsulphamate, which together accounted for 2.1+/-0.4% of the dose. 4. Directly coupled HPLC-NMR-MS and 19F-NMR spectroscopy is shown to provide an efficient approach for the unequivocal and rapid determination of the quantitative urinary metabolic fate and excretion balance of a fluorinated xenobiotic without the necessity for specific radiolabelling.     

Cephaloridine-induced nephrotoxicity in the Fischer 344 rat: proton NMR spectroscopic studies of urine and plasma in relation to conventional clinical chemical and histopathological assessments of nephronal damage

The acute toxicological effects of the nephrotoxic antibiotic cephaloridine (CPH, 0–1500 mg/kg) in male Fischer 344 (F344) rats, have been investigated over 48 h using clinical chemistry, histopathology and proton nuclear magnetic resonance (¹H NMR) spectroscopy of urine and plasma. High field (400 and 600 MHz)¹H NMR urinalysis revealed increased excretion of lactic acid, acetoacetate, alanine, valine, lysine, glutamine and glutamate and a severe, time-dependent glycosuria. A major change observed in urine of CPH-treated animals was the dose-dependent increase in HB which may relate to altered energy metabolism. CPH also caused dose-dependent decreases in the urinary excretion of hippurate, allantoin and protein (conventional assay). This abnormal metabolic profile is consistent with a functional defect in the S₁/S₂ regions of the proximal tubule, and was confirmed by histologypost mortem. Functional changes observed included elevations in blood urea nitrogen (BUN) and urine flow rate (UFR) and dose-related decreases in urine osmolality. Spin-echo¹H NMR spectroscopic analysis of lyophilised plasma, reconstituted with²H₂O revealed an abnormal phase modulation of the methyl signal from free alanine and it is postulated that this is due to the release of transaminases from damaged tissue which via a reversible conversion to pyruvate, cause variable deuteration of alanine at the -CH position. This observation suggests that¹H NMR spectral patterns are also dependent on the level of plasma transaminases and this may provide a novel indicator of tissue damage.