A longitudinal study of the persistence of increased creatinine and concordance between kidney biomarkers in cats and dogs.

Kidney disease causes morbidity and mortality in dogs and cats. Serum creatinine concentration is an important surrogate marker for glomerular filtration rate (GFR). However, it is not always sensitive to small decreases in kidney function. Efforts to identify additional, more sensitive surrogate markers of GFR to improve detection of early kidney disease has led to the use of symmetrical dimethylarginine (SDMA) in veterinary medicine. There is insufficient information about the behavior of creatinine after an increase and the expected behavior of creatinine and SDMA in these cats and dogs. This study assesses the probability of persistence of increases in creatinine and the subsequent behavior of creatinine and SDMA in animals with persistently increased creatinine. For enrollment, three paired SDMA and creatinine concentrations were required: baseline (T0) with creatinine and SDMA at or below the upper reference limit (URL), T1, and T2 0.5-18 months after T1. The study included 4517 cats and 4576 dogs with increased T1 creatinine concentrations and 54,295 cats and 125,403 dogs with T1 creatinine at or below the URL. The probability of a persistently increased creatinine at T2 was approximately 58% for cats and 49% for dogs after a T1 increase. For animals without a T1 increase the probability of increased creatinine at T2 was only 7% for cats and 3% for dogs. For cats and dogs with persistently increased Cr, the probability of an increased SDMA concentration at T1 was 70-75%. By 24 months, that probability rose to 94% for cats and 88% for dogs.

Longitudinal evaluation of symmetric dimethylarginine and concordance of kidney biomarkers in cats and dogs.

Symmetric dimethylarginine (SDMA) is a sensitive surrogate marker for glomerular filtration rate; however, there are uncertainties as to how to interpret mild increases (SDMA 15-19 µg/dL). This descriptive study used retrospective data to evaluate whether cats or dogs that had initial SDMA values (at T0) within the reference interval followed by an increased SDMA (at T1) had persistently increased SDMA (at T2; measured from 14 days to 18 months following T1; Persistence Cohort), and if and when cats or dogs with persistently increased SDMA had increased creatinine up to 24 months (Concordance Cohort). The Persistence Cohort included 16,670 cats and 16,712 dogs. If SDMA at T1 was 15-19 µg/dL, the probability of persistence was 53% for cats and 42% for dogs, while creatinine was concurrently increased in 20% of cats and 18% of dogs. For comparison, if SDMA was not increased at T1 the probability of increased SDMA at recheck was only 20% for cats and 9% for dogs. For cats and dogs with a T1 SDMA of 15-19 µg/dL and with persistent increases at T2, the probability of increased creatinine at T1 was 20% for cats and 18% for dogs, rising to 61% and 55%, respectively, by 24 months. When SDMA at T1 was >25 µg/dL, creatinine was increased in 93% of cats and 92% of dogs by 24 months. Mildly increased SDMA results may provide an opportunity to identify some cats and dogs earlier in their kidney disease.

Nitrate reductase activity and chlorophyll content in sun leaves of subtropical Australian closed-forest (rainforest) and open-forest communities.

A study of the sun leaves of two closed-forest (rainforest) and eight open-forest communities in subtropical southeast Queensland, Australia, showed that a large number of pioneer woody species in closed-forests had high levels of nitrate reductase (EC 1.6.6.1), whereas only a few herbaceous species in the open-forests showed high levels. There was a continuously declining gradient in nitrate reductase activity from pioneer to mature-forest species in all communities, associated with a decrease in Leaf Specific Area. The level of nitrate reductase activity was lower in certain plant families (including sclerophyllous monocotyledons, small-leaved composites and legumes), but still showed the same general relationship with Leaf Specific Area. The decrease in Leaf Specific Area is associated with an increase in both the dry weight: fresh weight ratio and the chlorophyll a: chlorophyll b ratio of the leaves. Three groups of plants can be recognised by nitrate reductase activity plotted against water content (% fresh weight) of their leaves-(1) pioneer, (2) mature-forest and (3) semi-sclerophyllous species. As the proportion of cytoplasm to structural tissue (indicated by water content) in leaves increases, there is a continuous increase in (a) nitrate reductase activity (b) total chlorophyll (per unit dry weight) (c) the proportion of chlorophyll b to chlorophyll a and (b) chloroplastic isoform of glutamine synthetase. These attributes are associated with high nitrogen content in the leaves and high photosynthetic potentials, resulting in rapid growth rates of pioneer species.

Case analysis as a teaching method in the paraclinical sciences.

A major problem in the teaching of the preclinical and paraclinical sciences to medical students is that courses are often taught in isolation from the clinical programme and students have difficulty relating the different types of learning experiences. This paper introduces case analysis as method designed to overcome this problem. The casebook method is popular with students and staff members and is a practical way of encouraging independent and motivated learning in the paraclinical sciences.

Additional factors influencing sensitivity in the tetramethyl benzidine method for horseradish peroxidase neurohistochemistry.

In experiments that use horseradish peroxidase (HRP) and tetramethyl benzidine (TMB) for tracing neural connections, the activity of tissue-bound enzyme as well as the stability of the resultant reaction product are influenced by the duration of storage, the composition of the storage medium, the type of counterstaining and even the details of histological dehydration. Furthermore, the conditions for preserving HRP activity are very different from those necessary for preserving the stability of the tetramethyl benzidine (TMB) reaction product. Thus, tissue-bound HRP activity is stable at a neutral pH, while a much lower pH, around 3.3, is required for preserving the stability of the TMB reaction product. Recent evidence indicates that the stabilization bath in sodium nitroferricyanide that was previously recommended is not necessary. However, gradual dehydration of mounted sections is essential for long-term stability. Excessive counterstaining and excessive dehydration interfere with the detection of reaction product. These considerations are pertinent to experiments using free HRP as well as to those where the enzyme has been conjugated to wheat germ agglutinin.

How to: organize effective laboratory teaching in medicine. Part 1, purposes.

Practical work is alive and well, but very different from the traditional 'exercises' and 'demonstrations' of 20 years ago. In the first of two articles the author describes occasions on which laboratory teaching can be most successfully used, ways in which laboratory instructions can be written and preparatory work organized, together with methods of monitoring progress. Examples are given of ways in which effective laboratory work for medical students can be designed.

How to : Organize Effective Laboratory Teaching in Medicine. Part 2, Design.

In this second article on laboratory teaching in medicine, the authors discuss the design of laboratory manuals and displays, the design of laboratory exercises to meet important goals of medical teaching, and the sequencing of curricula involving laboratory work. Readers are encouraged to consider laboratory classes in their own disciplines and within their own institutions, and to answer the questions set out in a check list provided by the authors at the end of the article.