Jennifer Lingard

Body fat distribution and total body fat as risk factors for microalbuminuria in the obese.

Background/Aim: Despite evidence linking type of obesity with subsequent organ malfunction, such a link with renal malfunction has not been widely researched. The aim of this study was to investigate percentage of total body fat (%TBF), and body fat distribution in relation to the renal function in overweight/obese subjects. Methods: Body mass index (BMI), waist-to-hip ratio (WHR), TBF (by bioelectric impedance), and albumin excretion rate (AER) were determined in 77 subjects: 48 overweight/obese (BMI ≧27.8 for men and ≧27.3 for women) and 29 controls (BMI <27.8 for men and <27.3 for women). Obese subjects were subdivided into those (n = 33) with central fat distribution (WHR ≧0.81 for women and ≧0.92 for men) and those (n = 15) with peripheral fat distribution (WHR <0.81 for women and <0.92 for men). Results: Obesity, irrespective of type, was significantly related to increased AER. Furthermore, in subjects who did not differ in %TBF, the age-adjusted relative risk of abnormal AER was 18 times greater in centrally obese subjects as compared with controls, while only four times greater in peripherally obese subjects. Conclusion: A significant difference in risk of renal malfunction was observed in individuals having the same %TBF, but differing in the distribution of this fat, with a central fat pattern being the greater risk.

Variation in student reflections on their conceptions of and approaches to learning biochemistry in a first-year health sciences' service subject

Many factors affect students’ learning approaches, including topic conceptions and prior study. This research, undertaken after a first‐semester compulsory subject, explores students’ conceptions of biochemistry and how they approached their studies. Students (n=151) completed an open‐ended survey analysed phenomenographically. Those with cohesive conceptions were found to be more likely to adopt deeper approaches to study than those with fragmented conceptions, a result unaffected by various demographic parameters. Compared with earlier research, a semester of study increased the percentage of students with a cohesive view, with no concomitant change in learning approaches, suggesting that cohesive conceptions are a necessary but not sufficient criterion for deep learning outcomes. Compared with results for a science major subject, more of the students with cohesive conceptions used surface approaches. This may reflect a regression to safe surface approaches when faced with an unfamiliar topic or high total workload driving a strategic approach to learning. It could also reflect a perception that this material is only a tool for later application. The present findings indicate the crucial importance, when university studies begin, of enabling students to build an overarching conception of the topic’s place in professional practice. This concept building should be applied across the entire curriculum to emphasize application and integration of material (key graduate attributes). Improved conceptions may provide crucial motivation for students to achieve deeper learning, especially in these foundation service subjects. These essential changes to the learning context may also better prepare students for increasing self‐directed/life‐long learning.

Reabsorption ofl-glutamine andl-histidine from various regions of the rat proximal convolution studied by stationary microperfusion: Evidence that the proximal convolution is not homogeneous

SummaryStationary microperfusion of the rat proximal convoluted tubule together with simultaneous perfusion of the peritubular blood capillaries has been used to studyl-histidine andl-glutamine transport in the rat kidney. When histidine and glutamine concentrations in the capillary perfusate were 14.1 and 6.9 mmol/kg respectively, the luminal concentrations stabilized at about 5.6 and 2.0 mmol/kg respectively. The transepithelial concentration differences at steady-state were 8 mmol/kg (histidine) and 5 mmol/kg (glutamine). The results indicated that when peritubular capillary concentrations were high enough, nett passive back-flux of amino acids down a concentration gradient can become of considerable importance in determining nett reabsorptive rates.When the steady-state epithelial concentration differences were analysed in relation to perfusion site within the proximal convolution, it was found that the gradient was greatest near the glomerulus and smallest near thepars recta, the rate of decline along the convolution being approximately linear. This inhomogeneity of the proximal tubule seems to be due to a diminution in nett amino acid transport by about 50%. The results correlate well with the observation in Fanconi syndrome (congenital renal aminoaciduria with rickets) that only the first 1/3 of the proximal tubule usually shows marked pathological changes.

Kinetics ofl-histidine transport in the proximal convolution of the rat nephron studied using the stationary microperfusion technique

SummaryThe kinetics ofl-histidine reabsorption by the proximal convolution of the rat nephron have been studied by stationary microperfusion with simultaneous perfusion of peritubular capillaries. Steady-state concentrations (C∞) and transepithelial concentration differences (Δc∞) were determined over a wide range of peritubular bistidine concentrations. It was found that Δc∞ increased hyperbolically with increase in luminal and peritubular histidine concentrations suggesting saturation transport kinetics. Furthermore Δc∞ declined linearly along the convolution suggesting that nett active transport was not constant throughout the tubule. Using an expression to describe the rate of attainment of steady-state concentration in terms of lummal and peritubular histidine concentrations, histidine permeability coefficient (P), the maximum rate of active histidine transport (Jmax) and the half saturation constant of the transport reaction (Km), we were able to determine the cause of the tubule inhomogeneity. We find thatP (14.1×10−5 cm/s) andJmax (45×10−10 mol/cm2· s) are constant along the convolution but thatKm increases markedly from about 5.4 mmol/kg 26% of the way along the convolution to 40 mmol/kg at 86%. These findings suggest that the histidine reabsorptive mechanism would be relatively inefficient with histidinuria occurring at all plasma concentrations but it would have enormous reserve capacity so that saturation would not readily occur. This prediction accords with available data on histidine clearance in the rat.

Relation between active sodium transport and distance along the proximal convolutions of rat nephrons: Evidence for homogeneity of sodium transport

SummaryThe transepithelial sodium (Na) concentration difference at steadystate (Δceq) was measured in the proximal convolutions of surface nephrons of the rat kidney using peritubular and stopped-flow microperfusion techniques. The measurements were made at various sites along the convolution over a wide range of intraluminal Na concentrations. Over a concentration range from 35 to 400 mmol/kg H2O no correlation was found between the size of Δceq and the location of the perfusion site within the convolution. It was concluded that the proximal convolution was homogeneous with respect both to theKm and theVmax of the Na transport system.

Comparison of a footpad analyser with a tetrapolar model for the determination of percent body fat in young men

Since excess weight in adolescence predisposes to overweight and obesity in adulthood, a simple measure of excess adiposity in adolescents is important. Fast, inexpensive, bioelectric impedance analysers (BIA) which rely on two foot pad electrodes are now available to measure % total body fat (TBF), but are less well investigated than conventional tetrapolar models which require the subject to lie prone with four electrodes attached to hands and feet. The aim of this study was to compare the estimation of % TBF by a foot pad analyser and a tetrapolar model. Male students, n = 35, 17-19 years had height, weight, waist and hip circumferences measured and completed a questionnaire regarding age, ethnicity and time of last eating and drinking. Percent TBF was measured by a Tanita stand-on analyser (Tanita 105, Tanita Corporation, Japan) and a SEAC tetrapolar model (SEAC, SFB3, QUT, Australia). Mean age (+/- SD) of subjects = 18.2 +/- 0.6 years, BMI = 24.4 +/- 3.5 kg/m2, WHR = 0.81 +/- 0.04, % TBF, Tanita = 18.2 +/- 6.2 and SEAC = 20.4+/-4.8. Both measures of fat were correlated (r = 0.84, p<0.0001). A plot of the average versus the difference of the two analysers found the majority of differences were above zero, especially for measures of fat below 22%, indicating a negative bias for the Tanita. The limits of agreement are between -5.4 and 9% TBF. Information provided by this study will guide gymnasium operators and health professionals to comment on a relative degree of adiposity with greater confidence of data reliability.

Microperfusion study of the kinetics of reabsorption of cycloleucine in early and late segments of the proximal convolution of the rat nephron

SummaryThe proximal tubular reabsorptive capacity for the non-metabolizable amino acid, cycloleucine, was studied in the rat nephron by stationary microperfusion. Tubular reabsorptive rates were greatest near the glomerulus and declined progressively along the convolution. A kinetic analysis of cycloleucine reabsorption in terms of luminal concentration revealed that this reduced transport rate was associated with an increase in the half-saturation constant of the kinetic curve, rather than a decrease in the maximum transport capacity. Since our previous findings with the metabolizable amino acid,l-histidine, were identical we can conclude that this decline in reabsorption of neutral amino acids as a function of distance along the convolution is an intrinsic property of the transport system and is not related to tubule cell amino acid metabolism.The transport curves for cycloleucine absorption did not give a simple Michaelis-Menten relation but rather followed a course suggesting that more than one transport system might be involved.

Adenylate cyclase activity in human pancreatic adenocarcinoma cell lines

SummaryConclusionBxPC-3, Hs 766T, Capan-2, Panc-1, and Capan-1 cells possess receptors for VIP and β-adrenergic agonists that are functionally coupled to adenylate cyclase. In this respect, they resemble pancreatic duct cells. However, we speculate that the process of neoplastic transformation has either downregulated the expression of secretin receptors or led to a defect in the receptor itself, placing a question mark over the usefulness of these adenocarcinoma cell lines as models of the pancreatic ductal epithelium.BackgroundBecause of the importance of ducts in pancreatic disease, we wished to establish which duct cells receptors are functional on adenocarcinoma cell lines.MethodsWe investigated the expression of agonist-stimulated adenylate cyclase activity in six human pancreatic adenocarcinoma cell lines. Known stimulants of pancreatic ductal secretion, VIP, PHI, secretin, β-adrenergic, and dopamine, were tested.ResultsFor responsive cell lines, VIP was the most effective stimulant followed by adrenaline, isoprenaline, PHI, and secretin. Dopamine was without effect. Since high concentrations of PHI and secretin were required to stimulate cyclase activity, their effect is probably mediated by VIP receptors. Based on the degree of stimulation observed with the individual agonists, Hs 766T and BxPC-3 were the most responsive cell lines, followed by Capan-2 and Capan-1, and finally Panc-1. MIAPaCa-2 cells did not respond to any of the agonists tested.

Acetylcholine, ATP, bombesin, and cholecystokinin stimulate 125I efflux from a human pancreatic adenocarcinoma cell line (BxPC-3)

We have studied the effects of acetylcholine (ACh), and other agents that modulate pancreatic bicarbonate secretion, on the anion permeability of a human ductal adenocarcinoma cell line (BxPC-3). Anion permeability was monitored using an 125I efflux assay. ACh (10 μM) markedly stimulated 125I efflux from BxPC-3 cells and this response was abolished by atropine (10μM), indicating that it is mediated by muscarinic receptors. Using transport inhibitors and ionophores, we obtained data indicating that some of the ACh-induced 125I efflux results from the opening of K+ channels, which would hyperpolarise the cell and increase the electrical driving force for lzSl exit. The remaining ACh-induced 125I efflux is not mediated by anion exchangers or by Na+/KC/2C1-cotransporters, and is probably explained by activation of an anion channel in the BxPC-3 cell membrane. Ionomy-cin (0.5 pkf) caused a small rise in 125I efflux, indicating that this process can be triggered by an increase in intra-cellular calcium concentration. ATP (100 μM), ADP (100 μM), bombesin (10 μM), and cholecystokinin (CCK) (10 μM) also stimulated 125I efflux, indicating that receptors for these agents are expressed on BxPC-3 cells. We speculate that bicarbonate secretion from the human pancreas could be modulated by ACh, ATP, bombesin, and CCK via a direct effect on the duct cell.

Do Students with Well-Aligned Perceptions of Question Difficulty Perform Better?

Effective criterion referenced assessment requires grade descriptors to clarify to students what skills are required to gain higher grades. But do students and staff actually have the same perception of the grading system, and if so, do they perform better than those whose perceptions are less accurately aligned with those of staff? Since students’ learning is influenced by their perception of the skills required to obtain high marks, it is important to learn what students think is being tested. The aims were thus to: 1. compare the student and staff perceptions of the grade descriptors associated with multiple‐choice questions (MCQs) and the factors that may underlie these student perceptions; 2. ascertain if students perform better when their perceptions of the grade descriptors are well‐aligned with staff judgements. Students studying biochemistry or physics were provided with appropriate online MCQs and were asked to indicate the correct content answers and their perception of the level of difficulty (as indicated by the appropriate grade descriptor) for each question. Detailed feedback on understanding of content and level of difficulty for each question was later provided online. A key finding is that student and staff agreement on perception of question difficulty is only about 50%, for either topic. The differences were significantly correlated with prior knowledge, entry level and exam mark for physics. The implications of these findings to the wider tertiary education community are discussed.