The monocyte-to-lymphocyte ratio: Sex-specific differences in the tuberculosis disease spectrum, diagnostic indices and defining normal ranges

Background

The monocyte-to-lymphocyte ratio (MLR) has been advocated as a biomarker in tuberculosis. Our objective was to evaluate its clinical value and associations.

Methods

Blood counts, inflammatory markers and clinical parameters were measured in patients with and those screened for tuberculosis. Complete blood counts (CBCs) from a multi-ethnic population aged 16 to 65 years were evaluated; a sub-group with normal hematological indices was used to define the range of MLRs.

Results

Multivariate analysis in proven tuberculosis (n = 264) indicated MLR associated with low serum albumin, high white cell counts and a positive culture; values were higher in sputum smear-positive pulmonary tuberculosis (S+PTB). Analysis in S+PTB (n = 296) showed higher MLRs in males and those with high neutrophil counts, low serum albumin and high C-reactive protein. The diagnostic value of MLRs was assessed by comparing notified patients with TB (n = 264) with denotified cases (n = 50), active case-finding in non-contacts (TB n = 111 and LTBI n = 373) and contacts of S+PTB (n = 149) with S+PTB found at screening (n = 75). Sensitivities and specificities ranged from 58.0–62.5% and 50.0–70.0% respectively for optimal cut-off values, defined by ROC curves. In CBCs obtained over one month, ratios correlated with neutrophil counts (ρ = 0.48, P<0.00001, n = 14,573; MLR = 0.45 at 8–8.9 x 10⁹/L) and were higher in males than females (P<0.0001). The MLR range (mean ± 2SD) in those with normal hematological indices (n = 3921: females 0.122–0.474; males 0.136–0.505) paralleled LTBI MLRs. Ratios did not predict death (n = 29) nor response to treatment (n = 178 S+PTB with follow-up CBCs). Ratios were higher in males than female in the 16–45 years age group, where immune differences due to sex hormones are likely greatest.

Conclusions

Severe tuberculosis and male sex associated with high MLRs; the same variables likely affect the performance of other biomarkers. The ratio performed poorly as a clinical aid.

Underwater caustics disrupt prey detection by a reef fish

Natural habitats contain dynamic elements, such as varying local illumination. Can such features mitigate the salience of organism movement? Dynamic illumination is particularly prevalent in coral reefs, where patterns known as 'water caustics' play chaotically in the shallows. In behavioural experiments with a wild-caught reef fish, the Picasso triggerfish (Rhinecanthus aculeatus), we demonstrate that the presence of dynamic water caustics negatively affects the detection of moving prey items, as measured by attack latency, relative to static water caustic controls. Manipulating two further features of water caustics (sharpness and scale) implies that the masking effect should be most effective in shallow water: scenes with fine scale and sharp water caustics induce the longest attack latencies. Due to the direct impact upon foraging efficiency, we expect the presence of dynamic water caustics to influence decisions about habitat choice and foraging by wild prey and predators.

Why UV vision and red vision are important for damselfish (Pomacentridae): structural and expression variation in opsin genes

Coral reefs belong to the most diverse ecosystems on our planet. The diversity in coloration and lifestyles of coral reef fishes makes them a particularly promising system to study the role of visual communication and adaptation. Here, we investigated the evolution of visual pigment genes (opsins) in damselfish (Pomacentridae) and examined whether structural and expression variation of opsins can be linked to ecology. Using DNA sequence data of a phylogenetically representative set of 31 damselfish species, we show that all but one visual opsin are evolving under positive selection. In addition, selection on opsin tuning sites, including cases of divergent, parallel, convergent and reversed evolution, has been strong throughout the radiation of damselfish, emphasizing the importance of visual tuning for this group. The highest functional variation in opsin protein sequences was observed in the short- followed by the long-wavelength end of the visual spectrum. Comparative gene expression analyses of a subset of the same species revealed that with SWS1, RH2B and RH2A always being expressed, damselfish use an overall short-wavelength shifted expression profile. Interestingly, not only did all species express SWS1 - a UV-sensitive opsin - and possess UV-transmitting lenses, most species also feature UV-reflective body parts. This suggests that damsels might benefit from a close-range UV-based 'private' communication channel, which is likely to be hidden from 'UV-blind' predators. Finally, we found that LWS expression is highly correlated to feeding strategy in damsels with herbivorous feeders having an increased LWS expression, possibly enhancing the detection of benthic algae.

Reflecting optics in the diverticular eye of a deep-sea barreleye fish (Rhynchohyalus natalensis)

We describe the bi-directed eyes of a mesopelagic teleost fish, Rhynchohyalus natalensis, that possesses an extensive lateral diverticulum to each tubular eye. Each diverticulum contains a mirror that focuses light from the ventro-lateral visual field. This species can thereby visualize both downwelling sunlight and bioluminescence over a wide field of view. Modelling shows that the mirror is very likely to be capable of producing a bright, well focused image. After Dolichopteryx longipes, this is only the second description of an eye in a vertebrate having both reflective and refractive optics. Although superficially similar, the optics of the diverticular eyes of these two species of fish differ in some important respects. Firstly, the reflective crystals in the D. longipes mirror are derived from a tapetum within the retinal pigment epithelium, whereas in R. natalensis they develop from the choroidal argentea. Secondly, in D. longipes the angle of the reflective crystals varies depending on their position within the mirror, forming a Fresnel-type reflector, but in R. natalensis the crystals are orientated almost parallel to the mirror's surface and image formation is dependent on the gross morphology of the diverticular mirror. Two remarkably different developmental solutions have thus evolved in these two closely related species of opisthoproctid teleosts to extend the restricted visual field of a tubular eye and provide a well-focused image with reflective optics.

Conspicuous visual signals do not coevolve with increased body size in marine sea slugs

Many taxa use conspicuous colouration to attract mates, signal chemical defences (aposematism) or for thermoregulation. Conspicuousness is a key feature of aposematic signals, and experimental evidence suggests that predators avoid conspicuous prey more readily when they exhibit larger body size and/or pattern elements. Aposematic prey species may therefore evolve a larger body size due to predatory selection pressures, or alternatively, larger prey species may be more likely to evolve aposematic colouration. Therefore, a positive correlation between conspicuousness and body size should exist. Here, we investigated whether there was a phylogenetic correlation between the conspicuousness of animal patterns and body size using an intriguing, understudied model system to examine questions on the evolution of animal signals, namely nudibranchs (opisthobranch molluscs). We also used new ways to compare animal patterns quantitatively with their background habitat in terms of intensity variance and spatial frequency power spectra. In studies of aposematism, conspicuousness is usually quantified using the spectral contrast of animal colour patches against its background; however, other components of visual signals, such as pattern, luminance and spectral sensitivities of potential observers, are largely ignored. Contrary to our prediction, we found that the conspicuousness of body patterns in over 70 nudibranch species decreased as body size increased, indicating that crypsis was not limited to a smaller body size. Therefore, alternative selective pressures on body size and development of colour patterns, other than those inflicted by visual hunting predators, may act more strongly on the evolution of aposematism in nudibranch molluscs.

Shrimps that pay attention: saccadic eye movements in stomatopod crustaceans

Discovering that a shrimp can flick its eyes over to a fish and follow up by tracking it or flicking back to observe something else implies a 'primate-like' awareness of the immediate environment that we do not normally associate with crustaceans. For several reasons, stomatopods (mantis shrimp) do not fit the general mould of their subphylum, and here we add saccadic, acquisitional eye movements to their repertoire of unusual visual capabilities. Optically, their apposition compound eyes contain an area of heightened acuity, in some ways similar to the fovea of vertebrate eyes. Using rapid eye movements of up to several hundred degrees per second, objects of interest are placed under the scrutiny of this area. While other arthropod species, including insects and spiders, are known to possess and use acute zones in similar saccadic gaze relocations, stomatopods are the only crustacean known with such abilities. Differences among species exist, generally reflecting both the eye size and lifestyle of the animal, with the larger-eyed more sedentary species producing slower saccades than the smaller-eyed, more active species. Possessing the ability to rapidly look at and assess objects is ecologically important for mantis shrimps, as their lifestyle is, by any standards, fast, furious and deadly.

To be seen or to hide: visual characteristics of body patterns for camouflage and communication in the Australian giant cuttlefish Sepia apama

It might seem obvious that a camouflaged animal must generally match its background whereas to be conspicuous an organism must differ from the background. However, the image parameters (or statistics) that evaluate the conspicuousness of patterns and textures are seldom well defined, and animal coloration patterns are rarely compared quantitatively with their respective backgrounds. Here we examine this issue in the Australian giant cuttlefish Sepia apama. We confine our analysis to the best-known and simplest image statistic, the correlation in intensity between neighboring pixels. Sepia apama can rapidly change their body patterns from assumed conspicuous signaling to assumed camouflage, thus providing an excellent and unique opportunity to investigate how such patterns differ in a single visual habitat. We describe the intensity variance and spatial frequency power spectra of these differing body patterns and compare these patterns with the backgrounds against which they are viewed. The measured image statistics of camouflaged animals closely resemble their backgrounds, while signaling animals differ significantly from their backgrounds. Our findings may provide the basis for a set of general rules for crypsis and signals. Furthermore, our methods may be widely applicable to the quantitative study of animal coloration.

Intraspecific cone opsin expression variation in the cichlids of Lake Malawi

The expression of cone opsin genes is a primary determinant of the characteristics of colour vision. Interspecific variation in opsin expression is common in African cichlids. It is correlated with foraging among cichlids from Lake Malawi, and with ambient light environment among cichlids from Lake Victoria. In this study, we tested whether gene expression varied within species such that it might be important in contributing to divergence. We hypothesized that light attenuation with depth would be correlated with predictable changes in gene expression in Lake Malawi, and that this variation would tune visual sensitivities to match the ambient light environment. We observed significant differences in cone opsin expression in three different comparisons among populations of the same species. Higher LWS expression was found in shallow versus deep Copadichromis eucinostomus. In Metriaclima zebra, individuals from Zimbawe Rock expressed significantly more SWS2B than those from Thumbi West Island, although these locales have similar ambient light environments. Finally, Tropheops gracilior from deeper water had significantly more variation in expression than their shallow counterparts. These results support that gene expression varies significantly between populations of the same species. Surprisingly, these results could not be explained by predicted visual performance as models predicted that differential expression patterns did not confer sensitivity advantages at different depths. This suggested that expression variation did not confer a local sensitivity advantage. Therefore, our findings were contrary to a primary requirement of the sensory bias hypothesis. As such, other explanations for intraspecific gene expression variation need to be tested.

Potential ultraviolet vision in pre-settlement larvae and settled reef fish—A comparison across 23 families

After hatching, larvae of coral reef fishes experience a pelagic phase during which they are diurnal planktivores. It has been suggested that ultraviolet (UV) vision is beneficial for the detection of planktonic prey. Aims were therefore to investigate whether ocular media of pre-settlement reef fish differ from those of respective adults, and whether larvae have UV-transparent ocular media required for UV vision. The ocular media of 84 pre-settlement and 98 adult species belonging to the same families were measured and compared. We suggest that adult lifestyle rather than planktivory in general shapes the ocular media properties of pre-settlement larvae.

Patients' perceptions of treatment with anti-TNF therapy for rheumatoid arthritis: a qualitative study

OBJECTIVES

Anti-tumour necrosis factor (anti-TNF) therapy is a highly effective treatment for rheumatoid arthritis (RA), as documented using standard outcome measures in clinical trials. Anecdotal experience suggests health benefits for patients other than those measured in this way. We wished to explore Patients' experience of and views about this treatment and the British Society for Rheumatology Biologics Registry (BSR BR) process.

METHODS

Separate focus groups for patients treated with infliximab (n = 7) and etanercept (n = 12) were undertaken. They were taped and transcribed verbatim, analysed and subjected to peer review and themes were identified.

RESULTS

Five main themes were identified: expectations of treatment, experience of treatment and its effects, concerns about taking a new class of drug, views about the BSR Biologics Registry process and costs.

CONCLUSIONS

Patients' experience of anti-TNF therapy was good, particularly in terms of physical function and well-being, although it did not live up to the very high expectations of some patients. The BSR BR process caused initial apprehension but patients had personal and altruistic reasons for being happy to comply with monitoring requirements. Qualitative methods add to our understanding of the effects of anti-TNF therapy for people with RA.

Increased prevalence of dental caries and poor oral hygiene in juvenile idiopathic arthritis

OBJECTIVES

Recent decades have seen a trend to treat juvenile idiopathic arthritis (JIA) with increasing immunosuppression to improve the long-term outcome. Poor oral hygiene and dental decay cause significant morbidity, and patients with chronic disease (who may be further immunocompromised by treatment) are at greater risk. This study investigated patients with JIA using standard measures of oral health.

METHODS

One hundred and forty-nine patients with JIA were included. The children were attending a regional paediatric rheumatology service and the adults were attending an adult rheumatology clinic. Random age- and sex-matched healthy controls were recruited from a dental teaching hospital. The structured dental examination included standard epidemiological indices of oral hygiene (gingival index, plaque index, oral cleanliness index) and dental decay [DMFT (decayed, missing or filled teeth) index].

RESULTS

JIA patients, at all ages, had increased levels of dental decay and poor oral hygiene. This increased level of decay was statistically significant in the patients aged 0-11 yr. Significant levels of untreated caries and increased levels of missing teeth were found in JIA, suggesting that patients with JIA had less restorative dental treatment, with tooth extraction often the chosen option for the treatment of dental decay.

CONCLUSIONS

This is the largest study of oral health in JIA and is cross-sectional with non-diseased controls. It shows significantly increased levels of poor oral hygiene and dental decay in patients with JIA. The high levels of untreated dental decay suggest barriers to dental care. These results emphasize the role of regular dental care in the multidisciplinary management of JIA.

Rapid colour changes in multilayer reflecting stripes in the paradise whiptail, Pentapodus paradiseus

The Paradise whiptail (Pentapodus paradiseus) has distinct reflective stripes on its head and body. The reflective stripes contain a dense layer of physiologically active iridophores, which act as multilayer reflectors. The wavelengths reflected by these stripes can change from blue to red in 0.25 s. Transmission electron microscopy revealed that the iridophore cells contain plates that are, on average, 51.4 nm thick. This thickness produces a stack, which acts as an ideal quarter-wavelength multilayer reflector (equal optical thickness of plates and spaces) in the blue, but not the red, region of the spectrum. When skin preparations were placed into hyposmotic physiological saline, the peak wavelength of the reflected light shifted towards the longer (red) end of the visible spectrum. Hyperosmotic saline reversed this effect and shifted the peak wavelength towards shorter (blue/UV) wavelengths. Norepinephrine (100 micromol l(-1)) shifted the peak wavelength towards the longer end of the spectrum, while adenosine (100 micromol l(-1)) reversed the effects of norepinephrine. The results from this study show that the wavelength changes are elicited by a change of approximately 70 nm in the distance between adjacent plates in the iridophore cells.

Conformational limitations of glycylsarcosine as a prototypic substrate for peptide transporters

Peptide transporters are present in all species to absorb the small peptides that occur ubiquitously as products of proteolysis. The broad substrate specificities of these systems allow them to be exploited therapeutically for delivery of peptidomimetic drugs in microbes and man. To this end, glycylsarcosine is currently used as a standard substrate for assaying peptidomimetic transport by peptide transporters. However, in this study we find it is unsuitable as a general substrate, based on assays of its transport by model bacterial peptide transporters and computer-based conformational analysis of its structure. Of the two generic transporters for di- and tripeptides, exemplified by Dpp and Tpp in Escherichia coli, only Dpp can transport glycylsarcosine. The explanation for this finding came from molecular modelling, which indicated that glycylsarcosine can adopt only a restricted range of conformers compared with typical dipeptides, and that of the conformers with a trans peptide bond, the majority have the specific psi and phi backbone torsion angles needed for molecular recognition and transport by Dpp but none possessed psi and phi torsions required for recognition by Tpp; moreover, 38% of its conformers have cis peptide bonds that are not substrates for any peptide transporter. Thus, using glycylsarcosine as substrate in competition assays with compounds that typically form conformers recognised by both types of peptide transporter will underestimate their transport. These findings have implications for assays of oral availability of peptidomimetic drugs such as beta-lactams, ACE inhibitors and anti-viral compounds, for which glycylsarcosine is routinely used.

Ocular media transmission of coral reef fish--can coral reef fish see ultraviolet light?

Many coral reef fish are beautifully coloured and the reflectance spectra of their colour patterns may include UVa wavelengths (315-400 nm) that are largely invisible to the human eye (Losey, G. S., Cronin, T. W., Goldsmith, T. H., David, H., Marshall, N. J., & McFarland, W.N. (1999). The uv visual world of fishes: a review. Journal of Fish Biology, 54, 921-943; Marshall, N. J. & Oberwinkler, J. (1999). The colourful world of the mantis shrimp. Nature, 401, 873-874). Before the possible functional significance of UV patterns can be investigated, it is of course essential to establish whether coral reef fishes can see ultraviolet light. As a means of tackling this question, in this study the transmittance of the ocular media of 211 coral reef fish species was measured. It was found that the ocular media of 50.2% of the examined species strongly absorb light of wavelengths below 400 nm, which makes the perception of UV in these fish very unlikely. The remaining 49.8% of the species studied possess ocular media that do transmit UV light, making the perception of UV possible.

Predominant torsional forms adopted by oligopeptide conformers in solution: parameters for molecular recognition

In this paper, we describe the predominant conformational forms adopted by tripeptides and higher oligopeptides in aqueous solution. About 50 tripeptides and almost 20 higher oligopeptides (4-6 residues) were subjected to conformational analysis using SYBYL Random Search. As with dipeptides (Grail BM, Payne JW. J. Peptide Sci. 2000; 6: 186-199), both tripeptides and higher oligopeptides were found to occupy relatively few combinations of psi-phi space that were distinct from those associated with predominant protein secondary structures (e.g. helices and beta-sheets). Again, the preferred psi (psi) values for the first residue (i - 1) were in sectors encompassed by the ranges from +150 degrees to +/-180 degrees, +60 degrees to +90 degrees and -60 degrees to -90 degrees, which were combined with preferred phi (phi) values for the second residue (i) in sectors with ranges from -150 degrees to +/-180 degrees, -60 degrees to -90 degrees and +30 degrees to +60 degrees. It was notable that tripeptides and, to a greater extent, higher oligopeptides adopted an initial psi (psi) (Tor2) from +150 degrees to +/-180 degrees. For tripeptides, their N-C distances (distance between N-terminal nitrogen and C-terminal carbon atoms) distribute about 6.5 A to give shorter, 'folded' conformers that are similar in length to dipeptides, and longer, 'extended' conformers that are distinct. Furthermore, for higher oligopeptides, their N-C distances did not increment in relation to their increasing number of residues and short, 'folded' conformers were still present. These findings have a bearing upon the recognition of these molecules as substrates for widely distributed peptidases and peptide transporters.

Structural basis for recognition of dipeptides by peptide transporters

Our objective in this work was to identify the structural basis for the molecular recognition of peptides by peptide transporters. Various assays for dipeptide transport by the dipeptide and tripeptide permeases of Escherichia coli were performed, together with measurements of thermodynamic parameters of substrate binding to the dipeptide binding protein using isothermal titration calorimetry. Computer-based conformational analysis of the test dipeptides was performed to define the repertoire of conformers that each dipeptide adopts in solution. Strict correlations were identified between the complement of particular conformers adopted by a peptide and its bioactivity as a substrate for each transporter. Details of the structural and electronic parameters that define the molecular recognition templates (MRTs) of the dipeptide substrates of these transporters are presented; similar MRTs are likely to apply with dipeptidases. These MRTs provide the essential information for the rational design of peptide-based drugs tailored for exploitation of peptide transporters in microorganisms and man.

Colour vision in billfish

Members of the billfish family are highly visual predatory teleosts inhabiting the open ocean. Little is known about their visual abilities in detail, but past studies have indicated that these fishes were likely to be monochromats. This study, however, presents evidence of two anatomically distinct cone types in billfish. The cells are arranged in a regular mosaic pattern of single and twin cones as in many fishes, and this arrangement suggests that the different cone types also show different spectral sensitivity, which is the basis for colour vision. First measurements using microspectrophotometry (MSP) revealed a peak absorption of the rod pigment at 484 nm, indicating that MSP, despite technical difficulties, will be a decisive tool in proving colour vision in these offshore fishes. When hunting, billfish such as the sailfish flash bright blue bars on their sides. This colour reflects largely in ultraviolet (UV) light at 350 nm as revealed by spectrophotometric measurements. Billfish lenses block light of wavelengths below 400 nm, presumably rendering the animal blind to the UV component of its own body colour. Interestingly, at least two prey species of billfish have lenses transmitting light in the UV waveband and are therefore likely to perceive a large fraction of the UV peak found in the blue bar of the sailfish. The possible biological significance of this finding is discussed.

Spectral tuning and the visual ecology of mantis shrimps

The compound eyes of mantis shrimps (stomatopod crustaceans) include an unparalleled diversity of visual pigments and spectral receptor classes in retinas of each species. We compared the visual pigment and spectral receptor classes of 12 species of gonodactyloid stomatopods from a variety of photic environments, from intertidal to deep water (> 50 m), to learn how spectral tuning in the different photoreceptor types is modified within different photic environments. Results show that receptors of the peripheral photoreceptors, those outside the midband which are responsible for standard visual tasks such as spatial vision and motion detection, reveal the well-known pattern of decreasing lambdamax with increasing depth. Receptors of midband rows 5 and 6, which are specialized for polarization vision, are similar in all species, having visual lambdamax-values near 500nm, independent of depth. Finally, the spectral receptors of midband rows 1 to 4 are tuned for maximum coverage of the spectrum of irradiance available in the habitat of each species. The quality of the visual worlds experienced by each species we studied must vary considerably, but all appear to exploit the full capabilities offered by their complex visual systems.

Transmission of ocular media in labrid fishes

Wrasses (Labridae) are the second largest family of fishes on the Great Barrier Reef (after the Gobiidae) and, in terms of morphology and lifestyle, one of the most diverse. They occupy all zones of the reef from the very shallow reef flats to deep slopes, feeding on a variety of fauna. Many wrasses also have elaborately patterned bodies and reflect a range of colours from ultraviolet (UV) to far red. As a first step to investigating the visual system of these fishes we measured the transmission properties of the ocular media of 36 species from the Great Barrier Reef, Australia, and Hawaii, California and the Florida Keys, USA. Transmission measurements were made of whole eyes with a window cut into the back, and also of isolated lenses and corneas. Based on the transmission properties of the corneas the species could be split into two distinct groups within which the exact wavelength of the cut-off was variable. One group had visibly yellow corneas, while the corneas of the other group appeared clear to human observers. Five species had ocular media that transmitted wavelengths below 400 nm, making a perception of UV wavelengths for those species possible. Possible functional roles for the different filter types are discussed.

Communication and camouflage with the same 'bright' colours in reef fishes

Reef fishes present the observer with the most diverse and stunning assemblage of animal colours anywhere on earth. The functions of some of these colours and their combinations are examined using new non-subjective spectrophotometric measurements of the colours of fishes and their habitat. Conclusions reached are as follows: (i) the spectra of colours in high spatial frequency patterns are often well designed to be very conspicuous to a colour vision system at close range but well camouflaged at a distance; (ii) blue and yellow, the most frequently used colours in reef fishes, may be good for camouflage or communication depending on the background they are viewed against; and (iii) reef fishes use a combination of colour and behaviour to regulate their conspicuousness and crypsis.

The pit organs of elasmobranchs: a review

Elasmobranchs have hundreds of tiny sensory organs, called pit organs, scattered over the skin surface. The pit organs were noted in many early studies of the lateral line, but their exact nature has long remained a mystery. Although pit organs were known to be innervated by the lateral line nerves, and light micrographs suggested that they were free neuromasts, speculation that they may be external taste buds or chemoreceptors has persisted until recently. Electron micrographs have now revealed that the pit organs are indeed free neuromasts. Their functional and behavioural role(s), however, are yet to be investigated.

Study of venous blood flow changes during laparoscopic surgery using a thermodilution technique

BACKGROUND

Many modalities exist to analyse those factors that contribute to venous stasis and deep venous thrombosis (DVT) during laparoscopic surgery. To the authors' knowledge intraoperative measurement of femoral venous blood flow has not yet been performed nor has the influence of sequential compression devices been assessed using this parameter.

METHODS

The thermodilution technique similar to that employed in cardiac output measurement was used to determine changes in blood flow in the right femoral vein during laparoscopic cholecystectomy. Deep venous thrombosis prophylaxis involved perioperative use of sequential compression devices and subcutaneous heparin 5000 U.

RESULTS

Pneumoperitoneum and the Trendelenburg position reduced femoral venous return in four of the six patients studied, but sequential compression devices failed to return blood flow to baseline in a predictable fashion.

CONCLUSIONS

Although the measurement of blood flow using thermodilution is regarded as a reliable technique, during general anaesthesia the results may be susceptible to haemodynamic variations related to the anaesthetic agents as well as to the laparoscopic procedure. In addition sequential compression devices (when used alone) may not provide adequate prophylaxis against DVT because they do not predictably increase femoral blood flow.

Eye design and color signaling in a stomatopod crustacean Gonodactylus smithii

Many species of stomatopod crustaceans have multiple spectral classes of photoreceptors in their retinas. Behavioral evidence also indicates that stomatopods are capable of discriminating objects by their spectral differences alone. Most animals use only two to four different types of photoreceptors in their color vision systems, typically with broad sensitivity functions, but the stomatopods apparently include eight or more narrowband photoreceptor classes for color recognition. It is also known that stomatopods use several colored body regions in social interactions. To examine why stomatopods may be so 'concerned' with color, we measured the absorption spectra of visual pigments and intrarhabdomal filters, and the reflectance spectra from different parts of the bodies of several individuals of the gonodactyloid stomatopod species, Gonodactylus smithii. We then applied a model of multiple dichromatic channels for color encoding to examine whether the finely tuned color vision was specifically co-evolved with their complex color signals. Although the eye design of stomatopods seems suitable for detecting color signals of their own, the detection of color signals from other animals, such as reef fishes, can be enhanced as well. Color vision in G. smithii is therefore not exclusively adapted to detect its own color signals, but the spectral tuning of some photoreceptors (e.g. midband Rows 2 and 3) enhances the contrast of certain color signals to a large enough degree to make co-evolution between color vision and these rather specific color signals likely.

Optimisation of growth hormone production by muscle cells using plasmid DNA

The production of peptide hormones by skeletal muscle tissue is a promising area of gene therapy. Skeletal muscle myogenesis can be induced in vitro, resulting in the fusion of mononucleate myoblasts to form multinucleate myotubes, and delivery vectors are first tested in vitro. C2C12 myoblasts transfected with pcDNA3-GH, which used the human cytomegalovirus (CMV) promoter, secreted immunoreactive GH with comparable biological activity to pituitary GH. Mouse myeloid leukaemia cells, which express the mouse GH receptor were used for the bioassay, and activation of these cells by GH was measured by a colorimetric microculture tetrazolium assay. Cells were incubated with a tetrazolium salt (MTS) and an intermediate electron acceptor (phenazine methosulphate, PMS), and formazan production was measured as optical density (O.D.) at 490 nm. The efficiencies of several plasmid expression vectors were compared in differentiated and non-differentiated muscle cells, as a function of bioactive GH secreted by the transfected cells. Ten-day differentiated C2C12 myotubes transfected with pcDNA3E-GH, which used the CMV promoter and a rat myosin light chain enhancer element, secreted significantly more biologically active GH than myotubes transfected with pcDNA3-GH (0.82 O.D. units+/-0.06 vs 0.57+/-0.05 respectively, P<0.001). This was consistent with reduced CMV promoter activity in myotubes. Myoblasts transfected with pcDNA3-GH secreted more bioactive GH than 10-day transfected myotubes (1.1+/-0. 1 vs 0.77+/-0.07 respectively). However, the responses were indistinguishable (both 1.0+/-0.09) if both the myotubes and myoblasts had been transfected with pcDNA3E-GH. Substitution of the vector pMHLC-GH, which used a muscle-specific truncated rabbit myosin heavy chain promoter, and the myosin enhancer resulted in a marked decrease in the responses to the conditioned medium from fused myotubes compared with the vectors pcDNA3-GH and pcDNA3E-GH (0. 24+/-0.02 vs 0.57+/-0.05 vs 0.82+/-0.06 respectively). We concluded that the combination of CMV promoter and myosin light chain enhancer in pcDNA3E-GH had the greatest expression efficiency of the several plasmid vectors which we investigated.

The role of colour in signalling and male choice in the agamid lizard Ctenophorus ornatus

Bright coloration and complex visual displays are frequent and well described in many lizard families. Reflectance spectrometry which extends into the ultraviolet (UV) allows measurement of such coloration independent of our visual system. We examined the role of colour in signalling and mate choice in the agamid lizard Ctenophorus ornatus. We found that throat reflectance strongly contrasted against the granite background of the lizards' habitat. The throat may act as a signal via the head-bobbing and push-up displays of C. ornatus. Dorsal coloration provided camouflage against the granite background, particularly in females. C. ornatus was sexually dichromatic for all traits examined including throat UV reflectance which is beyond human visual perception. Female throats were highly variable in spectral reflectance and males preferred females with higher throat chroma between 370 and 400 nm. However, female throat UV chroma is strongly correlated to both throat brightness and chest UV chroma and males may choose females on a combination of these colour variables. There was no evidence that female throat or chest coloration was an indicator of female quality. However, female brightness significantly predicted a female's laying date and, thus, may signal receptivity. One function of visual display in this species appears to be intersexual signalling, resulting in male choice of females.

Molecular recognition templates of peptides: driving force for molecular evolution of peptide transporters

Small peptides derived from protein hydrolysis occur ubiquitously. To utilize these structurally diverse compounds, organisms possess generic peptide transporters for di- (Dpp), tri- (Tpp), and oligopeptides (Opp). Using conformational analysis, we describe the predominant conformers of di-, tri-, and oligopeptides in water; dipeptides occur as nine main groups, defined by specific combinations of torsional angles. The molecular recognition templates (MRTs) of substrates for Dpp and Tpp comprise distinct groups of dipeptide conformers plus folded tripeptide conformers with matching spatial distribution of recognition features; for Opp, the MRT involves specific oligopeptide conformers with extended backbones. For any peptide, the proportion of its conformers in a particular MRT correlates with its relative binding and transport by each transporter. Thus, peptide transporters have evolved complementary specificities to optimize utilization of the universal peptide pool. The general applicability of MRTs should facilitate rational design and targeting of peptide-based prodrugs.

Substrate specificity of the periplasmic dipeptide-binding protein from Escherichia coli: experimental basis for the design of peptide prodrugs

Pure dipeptide-binding protein (DppA) from Escherichia coli was studied in a filter binding assay to determine its binding specificity. A substrate:DppA stoichiometry of 1:1 was found with both [14C]AlaAla and Ala[14C]Phe. Surprisingly, substrate binding did not vary over the pH range pH 3-9.5. Different dipeptides yielded liganded protein with various pI values, implying that DppA can undergo subtly different conformational changes to accommodate different substrates. Using [125I]Tyr-peptides as substrates in competition assays, the relative binding affinities for a range of dipeptides were found to parallel their overall transport rates into E. coli through the dipeptide permease (Dpp), showing that DppA alone controls the specificity of Dpp. With a series of substituted glycyl peptides, binding affinity was progressively enhanced by alkylation (with methyl to butyl) of the N-terminal alpha-amino group. Thus, results from this approach provide an essential experimental basis, which complements the information from the crystal structure of DppA, for the design of peptidomimetic antibacterials targeted for transport through Dpp.

Tetrachromacy, oil droplets and bird plumage colours

There is a growing body of data on avian eyes, including measurements of visual pigment and oil droplet spectral absorption, and of receptor densities and their distributions across the retina. These data are sufficient to predict psychophysical colour discrimination thresholds for light-adapted eyes, and hence provide a basis for relating eye design to visual needs. We examine the advantages of coloured oil droplets, UV vision and tetrachromacy for discriminating a diverse set of avian plumage spectra under natural illumination. Discriminability is enhanced both by tetrachromacy and coloured oil droplets. Oil droplets may also improve colour constancy. Comparison of the performance of a pigeon's eye, where the shortest wavelength receptor peak is at 410 nm, with that of the passerine Leiothrix, where the ultraviolet-sensitive peak is at 365 nm, generally shows a small advantage to the latter, but this advantage depends critically on the noise level in the sensitivity mechanism and on the set of spectra being viewed.

The eyes of deep-sea fish. I: Lens pigmentation, tapeta and visual pigments

Deep-sea fish, defined as those living below 200 m, inhabit a most unusual photic environment, being exposed to two sources of visible radiation; very dim downwelling sunlight and bioluminescence, both of which are, in most cases, maximal at wavelengths around 450-500 nm. This paper summarises the reflective properties of the ocular tapeta often found in these animals, the pigmentation of their lenses and the absorption characteristics of their visual pigments. Deep-sea tapeta usually appear blue to the human observer, reflecting mainly shortwave radiation. However, reflection in other parts of the spectrum is not uncommon and uneven tapetal distribution across the retina is widespread. Perhaps surprisingly, given the fact that they live in a photon limited environment, the lenses of some deep-sea teleosts are bright yellow, absorbing much of the shortwave part of the spectrum. Such lenses contain a variety of biochemically distinct pigments which most likely serve to enhance the visibility of bioluminescent signals. Of the 195 different visual pigments characterised by either detergent extract or microspectrophotometry in the retinae of deep-sea fishes, ca. 87% have peak absorbances within the range 468-494 nm. Modelling shows that this is most likely an adaptation for the detection of bioluminescence. Around 13% of deep-sea fish have retinae containing more than one visual pigment. Of these, we highlight three genera of stomiid dragonfishes, which uniquely produce far red bioluminescence from suborbital photophores. Using a combination of longwave-shifted visual pigments and in one species (Malacosteus niger) a chlorophyll-related photosensitizer, these fish have evolved extreme red sensitivity enabling them to see their own bioluminescence and giving them a private spectral waveband invisible to other inhabitants of the deep-ocean.

Release of bioactive human growth hormone from a biodegradable material: poly(epsilon-caprolactone)

We have characterized the biodegradable material poly(epsilon-caprolactone) (PCL) as a delivery system for recombinant human growth hormone (hGH). Two contrasting methods for the manufacture of the biomaterial were investigated: namely, solvent casting and solvent casting particulate leaching; the latter yielded porous PCL discs. The degree of porosity, which was assessed by scanning electron microscopy, could be controlled by incorporating selected concentrations of particulate sodium chloride during the manufacturing process. Bioactive hGH released from the PCL preparations was quantified with a highly sensitive and precise bioassay which was based upon hGH activation of rat lymphoma Nb2 cells. Eluates obtained from control discs of PCL which had not been loaded with hGH proved to be nontoxic when tested on these cells. The release of bioactive hGH from hormone-loaded nonporous discs of PCL was found to be a direct function of the initial hormone loading dose. Increased porosity of the discs manufactured by solvent casting particulate leaching increased the delivery of hGH from discs which had been immersion loaded. However, hGH release after surface loading was independent of porosity. Hormone concentrations were also assessed by immunoassay so that the ratios of bio- to immunoactivity (B:I ratio) of the hormone release could be determined. We found that the B:I ratio of the hormone after release from unstored discs was identical to that of the hormone prior to its incorporation into the PCL, demonstrating that the mild incorporation procedures utilized had not adversely affected the structural integrity of the hormone. However, if the hormone-loaded discs were stored at 37 degrees C prior to elution, the B:I ratios of the hGH released decreased indicating that this compromised the bioactive site.

Stomatopod photoreceptor spectral tuning as an adaptation for colour constancy in water

Where colour is used in communication absolute judgement of signalling spectra is important, and failures of colour constancy may limit performance. Stomatopod crustaceans have unusual eyes in which the midband contains ten or more classes of photoreceptor. For constancy based on receptor adaptation to a fixed background, elementary theory predicts and we confirm by modelling, that stomatopods' narrow-band receptors outperform more broadly tuned receptors. Similar considerations could account for the small spectral separation of receptors in each midband row. Thus, stomatopods seem to trade-off sensitivity and signal-to-noise ratio for increased colour constancy.

Antibacterial efflux systems

Drug efflux, unidirectional pumping of cytotoxic drugs, is a major mechanism of antimicrobial multiresistance in bacteria. Although these efflux systems are usually chromosomally encoded, some are present on plasmids. Some of the efflux pumps are relatively well known: Emr and Acr system in Escherichia coli, whose outer membrane protein seems to be the multifunctional To1C; the mex efflux system described in Pseudomonas aeruginosa and ABC-type in Gram-negative bacteria. Also the role of efflux in Gram-positive bacteria are reviewed including Bacillus, Staphylococcus and Streptomyces.

Acromegaly or chronic renal failure: a diagnostic dilemma

Uraemic patients may have markedly elevated serum GH concentrations yet, for hitherto unknown reasons, they do not develop acromegaly. We discuss the diagnostic dilemma presented by a 33-year-old Caucasian male with chronic renal failure (creatinine clearance 10 ml/min) secondary to polycystic kidney disease, elevated GH concentrations (fasting concentration of 22.6 rising to 77.9 mU/l 30 minutes after a 75-g oral glucose load) as well as acromegalic features. Review of the patient's relatives and the findings of a normal serum IGF-I concentration and a normal pituitary fossa on magnetic resonance imaging, suggest that the patient's acromegalic appearance is a familial trait and his abnormal GH dynamics a result of his renal failure rather than acromegaly. The patient's normal GH bioactivity and reduced GH binding protein concentration supports the current belief that chronic renal failure leads to an increase in peripheral tissue resistance to GH due to decreased GH receptor numbers. These changes, together with reduced IGF-I bioactivity, may explain why patients with chronic renal failure do not develop acromegaly in the presence of abnormally elevated levels of GH.

Investigation into the release of bioactive recombinant human growth hormone from normal and low-viscosity poly(methylmethacrylate) bone cements

Previous studies showed that recombinant human growth hormone (hGH) released from hormone-loaded poly(methylmethacrylate) (PMMA) cement stimulated osteoid formation in a rabbit model. Local delivery of hGH from cemented hip arthroplasties may thereby provide a means of reducing the problem of aseptic loosening. We have investigated two different formulations of PMMA as delivery systems for bioactive hGH. The bioactivity of the hormone release in vitro was monitored with an eluted stain assay (ESTA). The hGH was also measured by an immunoassay, which provides an alternative assessment of structural integrity of the hormone released. In addition, we adapted the ESTA bioassay to assess the in vitro cytotoxicity of the cements. Using unloaded cements, the undiluted eluates from both types of PMMA proved cytotoxic. This cytotoxicity could be diluted out, and the procedure allowed us to measure the bioactivity of hGH in the eluates from hormone-loaded cements independent of their cytotoxicity. The major fraction of the bioactivity was released from both of the PMMA cements during the first 24 h, but the hormone remained detectable in eluates collected after 36 days of elution. Comparison of the bio- and immunoactivity of the hGH released showed that the ratio of these two activities (i.e., the B:I ratio) was constant over this time period. However in parallel studies in which hormone-loaded discs were stored under dry conditions prior to elution, we found that the B:I ratio then declined markedly. This suggests that fully hydrated conditions, such as when the discs are bathed in assay medium, are necessary to maintain the bioactivity of the hGH. Both cements released only approximately 1% of the hormone originally incorporated, but the hGH concentration which accumulated in the eluates were high in physiologic terms (approximately 1000 mU/L).

Effect of co-monomer composition on the integrity of bioactive growth hormone released from novel PEMA based polymers

The release of human growth hormone (hGH) from hormone loaded bone cement was previously shown to enhance osteoid formation. hGH is a complex protein and its incorporation into such cements may compromise its bioactivity. We therefore characterized the release of hGH from a series of methacrylate systems based upon poly(ethylmethacrylate) (PEMA). Different mixtures of two monomers, hydroxyethylmethacrylate (HEMA) and n-butylmethacrylate (n-BM) were used to provide polymers with graded water uptakes. Exclusive use of only one of the monomers resulted in enhanced cytotoxicity and also reduced release of the bioactive hormone. Combinations of the monomers improved the recovery of bioactivity from the polymers and reduced their cytotoxicity. hGH released from the polymer with the lowest water uptake (100% n-BM, 0% HEMA) had an exceptionally low bioactivity: immunoactivity ratio, suggesting that the bioactive site of the hormone is particularly susceptible to disruption when it is incorporated into this matrix.

The use of intermediate electron acceptors to enhance MTT bioreduction in a microculture tetrazolium assay for human growth hormone

We contrast the effects of three intermediate electron acceptors (IEAs) on the highly quantitative ESTA bioassay for human growth hormone. This is a microculture tetrazolium assay based upon the in vitro reduction of the tetrazolium salt MTT, by Nb2 cells which have been activated with hGH. Each of the IEAs influenced MTT-formazan production in a distinctive manner. The two quinonoids, namely menadione and co-enzyme Q0 markedly increased the MTT-formazan produced by hormone activated Nb2 cells and thereby amplified the response of our bioassay for human growth hormone (hGH). The exceptionally low bioassay baseline which is characteristic of the unstimulated Nb2 cells when only MTT is added was retained in the presence of CoQ0, but was greatly increased by menadione. Phenazine methosulphate, which is the most widely used redox intermediary in microculture tetrazolium assays, also increased the baseline, but had only a minimal additional effect on MTT reduction by activated Nb2 cells. We conclude that CoQ0 is the preferred IEA for this ESTA bioassay for hGH.

Growth hormone-responsive DT-diaphorase-mediated bioreduction of tetrazolium salts

Microculture tetrazolium assays (MTAs) rely upon the bioreduction of tetrazolium salts to their intensely coloured formazans. Although these assays are being extensively used, the intracellular mechanisms responsible for the formazan production are not known. MTAs currently provide the basis for uniquely precise in vitro bioassays for human growth hormone (hGH) which use the Nb2 cells. We have compared two contrasting tetrazolium salts, namely 3-(4,5-dimethyl-thiazol-2-yl)- 2,5-diphenyltetrazolium bromide (MTT) and 5-(3-carboxymethoxyphenyl)-2-(4,5-dimethylthiazolyl)-3-(4-++ +sulfophenyl) tetrazolium, inner salt (MTS), in this system. An intermediate electron acceptor (IEA) is obligatory for the MTS- but not the MTT-bioassay. We report that inhibitors of DT-diaphorase abolished MTS- but not MTT-formazan production. We conclude that substitution of MTT with MTS/menadione resulted in formazan production via a different electron transfer pathway which is exclusively mediated by DT-diaphorase.

Evaluation of growth hormone (GH) responses to pulsed GH-releasing hormone administration using the MTT-ESTA bioassay

We compared the immunoactivity of human growth hormone (hGH) with its bioactivity after stimulation of hGH release into the circulation by the administration of growth hormone-releasing hormone [GHRH(1-29)-NH2] according to a pre-determined protocol to four normal adult volunteers. We used the Hybritech immunoradiometric assay to measure the immunoactive GH concentrations. Bioactive GH concentrations were measured using the highly quantitative and precise eluted stain bioassay system (ESTA). The high sample capacity of the ESTA bioassay permitted us to monitor the bioactivities in closely timed sequential samples, and in far greater detail than has previously been possible. Two pulses of GHRH(1-29)-NH2 were administered intravenously to the four adult male volunteers (aged 24-37 years) on a weekly basis over a 4-week period. Two different doses of GHRH(1-29)-NH2 (0.1 and 1.0 micrograms/kg) were tested. These were separated by specified time intervals (60 or 120 min). Responses in the four individuals were variable. However, although the immuno- and bioactivities generally agreed well, there was a systematic and progressive increase in the bioactivity/immunoactivity (B/I) ratios as half of the response peaks were approached. After these peak concentrations, the B/I ratios subsequently returned to values that were close to unity. The enhanced bioactivity of the peak samples from the two volunteers in whom the largest magnitudes of response were observed was found to be labile after long-term storage at -20 degrees C. We suggest that the preferential rise in GH bioactivity, as opposed to immunoactivity, in response to GHRH(1-29)-NH2 was due to progressive changes in the concentrations of isoforms of GH that are not detectable in the Hybritech immunoassay.

An investigation into the lability of the bioactivity of human growth hormone using the ESTA bioassay

We compared the bioactivity attributable to human growth hormone (hGH) in serum samples, determined at the time of their collection, with that after storage for 2-18 months at -20 degrees C. The samples were obtained from volunteers and patients who underwent provocative tests of hGH secretion, and the bioactivity was determined in the ESTA bioassay, which is based upon the use of Nb2 cells. We report that, in some subjects, the bioactivity of samples collected at the response peaks deteriorated on storage for as little as 2 months. The decrease in hGH bioactivity was systematic in that it consistently declined so as to approach the values initially determined by an immunoassay (Hybritech IRMA). This differential lability was a characteristic of the peak samples, and was not observed for either samples collected before and after the peaks of hGH secretion or for purified preparations of hGH which were subjected to a range of freeze/thaw and storage regimens. We suggest that this unusual lability is indicative of transient shifts in the spectrum of the variants of hGH which are present in the circulation following stimulation by provocative agents. This study emphasises the need to minimise the risk of introducing storage artefacts in investigations into the responses of hGH to provocation.

The measurement of growth hormone bioactivity in patient serum using an eluted stain assay

We have adapted the MTT-ESTA bioassay for human GH (hGH) to measure the lactogenic bioactivity of the hormone in human serum. This highly quantitative in vitro colorimetric bioassay is based upon the reduction of a tetrazolium salt, 3-[4,5-dimethyl-thiazol-2-yl]2,5-diphenyl tetrazolium bromide (MTT), to its formazan by lactogen-activated Nb2 cells. Relatively high concentrations of human serum (1-10%) modified responses to the hormone in a complex manner. As the serum effects varied between samples, it proved impossible to adapt the bioassay by the conventional approach of using a lactogen-depleted serum as a representative matrix. However, as the Nb2 cells were exceptionally sensitive to hGH, the serum effects could be diluted out. We adopted a dilution strategy by which all samples of human serum were included in the bioassay at a concentration of 0.625% or less. A valid assay was obtained, as judged by the criteria of parallelism between diluted samples and hGH standards, and recoveries of spiked samples that were close to 100%. Hormonal specificity was achieved with the use of a highly specific anti-PRL antiserum. A within-assay precision of between 2-5% over the dose range of 0.03-0.96 microgram hGH/L was attained. As only highly diluted samples could be used, the sensitivity of the clinical bioassay was 1.2-2.4 micrograms hGH/L. The between-assay precision was estimated to be 11% and 9% at initial hGH concentrations in serum of 4.8 and 19.2 micrograms hGH/L, respectively. By exploiting the high sample capacity of the eluted stain bioassay system, we followed the changes in bioactivity and immunoactivity of hGH in multiple timed samples after stimulation of hGH secretion in an adult by GHRH. Systematic and progressive changes were observed in the bioactive/immunoactive ratios. Analogous changes were observed after insulin-induced hypoglycemia in a child with short stature. We speculate that the changes in the bioactive/immunoactive ratios reflect alterations in the proportions of the isoforms of hGH in the circulation after acute stimulation.

A critical assessment of the use of microculture tetrazolium assays to measure cell growth and function

Microculture tetrazolium assays (MTAs) are being widely applied to probe the relationships between cell survival, growth, and differentiation and also to investigate associations between compromised cell metabolism, oxidative stress, and programmed cell death as occurs in apoptosis. MTAs rely upon the cellular reduction of tetrazolium salts to their intensely coloured formazans. The resulting colorimetric assays form the basis of exceptionally precise systems which are technically amenable and capable of a high throughput of samples. As a consequence, MTAs are being used to monitor responses to both extracellular activators and toxic agents in disciplines as diverse as radiobiology and endocrinology. We review the chemistry and histochemical applications of tetrazolium salts and subsequently discuss the criteria for their use in MTAs. These assays are one of the latest examples of the application of the tetrazolium/formazan system to cell biology. We outline current views on the mechanisms of the bioreduction of tetrazolium salts. These probably combine to reflect the integrated pyridine nucleotide dependent redox state of the cell. We try to illustrate how an understanding of these mechanisms helps to avoid some of the pitfalls of the MTA systems. There is now for example, extensive evidence that changes in cell culture environments, such as glucose supply or pH of the medium, influence the reduction of tetrazolium salts and thereby introduce artefacts into MTAs. Finally, we provide examples of situations in which MTAs can be used to complement other more established experimental systems. They then act as unique probes with which to investigate changes in the redox state of the cell. These changes are associated with regulation of cell growth, proliferation and differentiation and conversely, the different pathways leading to cell death.

G120R, a human growth hormone antagonist, shows zinc-dependent agonist and antagonist activity on Nb2 cells

Substitution of arginine for glycine at position 120 in native 22-kDa human growth hormone (hGH) results in an analogue, G120R, which is unable to dimerize the GH receptor and is widely used to probe the molecular mechanism of action of hGH. When acting on human GH receptors, G120R antagonizes several biological effects of hGH, but is itself inactive as an agonist. It has been reported that this mutant also antagonizes hGH activation of the rat or human prolactin (PRL) receptor in cell-based assays, with no agonist activity. We have now tested this mutant in a sensitive MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide)-ESTA (eluted stain assay) bioassay using rat PRL receptors in the Nb2 cell line. We confirm that G120R acts as an efficient antagonist of native hGH, but show that it can also act as an agonist to generate intracellular signals leading to metabolic activation and proliferation of Nb2 cells. We have demonstrated an unusual sensitivity to the presence of zinc (Zn2+). In the absence of added Zn2+, G120R shows weak but full agonist activity in the bioassay, and this can be blocked by co-incubation with recombinant hGH-binding protein. G120R can therefore be utilized to discriminate between the molecular mechanisms of hGH interactions with its somatogenic and lactogenic receptors. Future studies with G120R in the rat may need to take account of its significant agonist effects on PRL receptors.

Perichondrial arthroplasty incorporating costal cartilage

A technique of IP joint arthroplasty is described using costal cartilage with accompanying perichondrium. All patients presented following trauma to the IP joints; their ages ranging from 15 to 45 years. Five out of six cases showed improvement of symptoms and function following reconstruction of the traumatized joint.

The development of an eluted stain bioassay (ESTA) for human growth hormone

The basic characteristics of MTT-formazan production by both quiescent Nb2 cells and those activated by fetal calf serum or human growth hormone (hGH) are described. These characteristics are exploited for the development of an MTT-ESTA bioassay for purified preparations of lactogens such as growth hormone. The resulting in vitro bioassay is sensitive and precise, with a detection limit of about 0.05 mU hGH/l (19 ng/l) and a within-assay imprecision of 2.5% in the presence of 0.3 mU hGH/l (114 ng/l). When utilizing quiescent Nb2 cells for bioassays, large magnitudes of response are observed. The major component of the response is clearly derived from metabolic activation of the cells, rather than increased cell proliferation. The response was abolished by anti-human growth hormone. Delayed addition of the latter demonstrated that the presence of the hormone is required for the entire 96 h of the recommended bioassay incubation period to obtain the maximum response. At high doses, the dose-response relationship reaches a prolonged plateau which covers 4 orders of magnitude of incremental hormone concentrations. A decline in response is observed at the highest dose tested, 10(6) mU hGH/l (385 mg/l). This auto-inhibition is consistent with recent reports of a reduction in response due to stoichiometric blockade of sequential receptor dimerisation which is crucial for activation of both somatogenic and lactogenic receptors by hGH.

Microculture tetrazolium assays: a comparison between two new tetrazolium salts, XTT and MTS

Microculture tetrazolium assays are being widely exploited to investigate the mechanisms of both cell activation and cell damage. They are colorimetric assays which are based upon the bioreduction of a tetrazolium salt to an intensely coloured formazan. We contrast the responses obtainable with two new tetrazolium salts, MTS and XTT, when used on the rat lymphoma cell line (Nb2 cells), which has been activated by human growth hormone. These tetrazolium salts, unlike the more commonly used MTT, form soluble formazans upon bioreduction by the activated cells. This has the advantage that it eliminates the error-prone solubilisation step which is required for the microculture tetrazolium assays which employ MTT. Bioreduction of XTT and MTS usually requires addition of an intermediate electron acceptor, phenazine methosulphate (PMS). We found that the XTT/PMS, but not the MTS/PMS, reagent mixture was unstable. Nucleation and crystal formation in the XTT/PMS reagent mixture, prepared in DPBS, could occur within 1-3 min. This resulted in a decline in XTT-formazan production and manifested itself in the microculture tetrazolium assay as both poor within-assay precision and serious assay drift. Several features of the system suggested that the formation of charge-transfer complexes between XTT and PMS accounted for this instability. No such instability was encountered when MTS and PMS were mixed. We demonstrate that MTS/PMS provides microculture tetrazolium assays for hGH which are free from these serious artefacts and which are uniquely precise. In conclusion we therefore advocate the use of MTS in preference to XTT for the new generation of microculture tetrazolium assays.

Specialization of retinal function in the compound eyes of mantis shrimps

Visual function and its specialization at the level of the retina were studied in 13 species of stomatopod crustaceans, representing three superfamilies: Gonodactyloidea, Lysiosquilloidea, and Squilloidea. We measured attenuation and irradiance spectra in the environment of each species, at the actual depths and times of activity where we observed individuals. We also characterized the intrahabdomal filters of all study species and determined the absolute spectral sensitivity functions and approximate photon capture rates of all photoreceptor classes below the level of the 8th retinular cell in seven of these species. Shallow-water gonodactyloid species have four distinct classes of intrarhabdomal filters, producing photoreceptors that are relatively insensitive but which have the broadest spectral coverage of all. Deep-water gonodactyloids and all lysiosquilloids have filters that are spectrally less diverse. These species often discard the proximal filter classes of one or more receptor types. As a result, their retinas are more sensitive but have reduced spectral range or diversity. The single squilloid species has the most sensitive photoreceptors of any we observed, due to the lack both of intrarhabdomal filters and tiered photoreceptors. Photon absorption rates, at the times of animal activity, were similar in most photoreceptor classes of all species, whether the receptors were tiered or untiered, or filtered or unfiltered. Thus, the retinas of stomatopods are specialized to operate at similar levels of stimulation at the times and depths of actual use, while evidently maintaining the greatest possible potential for spectral coverage and discrimination.

Ultraviolet photoreception in mantis shrimp

An UV-sensitive class of photoreceptors exists in all regions of the retinas of mantis shrimps. UV photosensitivity apparently resides in rhabdomeres of the eighth retinular cell (R8) that lies atop each rhabdom; and in ommatidia where the R8 rhabdomere consists of microvilli parallel in a single direction, sensitivity is maximal when the e-vector of plane-polarized light is parallel to the microvilli. Spectral sensitivity of the UV photoreceptor peaks at 345 nm and is best explained by the presence of a photopigment with lambda max near 325 nm overlain by material that absorbs UV light at wavelengths below approximately 350 nm. Rhabdomeres of R8 cells in several different retinal regions of a variety of species examined contain a photopigment absorbing maximally below 340 nm. Under appropriate conditions, a metapigment with lambda max near 460 nm can be formed. UV vision may be useful for enhancing the visual contrast of midwater predators or prey.