The evolution of coloration and toxicity in the poison frog family (Dendrobatidae)

The poison frogs (family Dendrobatidae) are terrestrial anuran amphibians displaying a wide range of coloration and toxicity. These frogs generally have been considered to be aposematic, but relatively little research has been carried out to test the predictions of this hypothesis. Here we use a comparative approach to test one prediction of the hypothesis of aposematism: that coloration will evolve in tandem with toxicity. Recently, we developed a phylogenetic hypothesis of the evolutionary relationships among representative species of poison frogs, using sequences from three regions of mitochondrial DNA. In our analysis, we use that DNA-based phylogeny and comparative analysis of independent contrasts to investigate the correlation between coloration and toxicity in the poison frog family (Dendrobatidae). Information on the toxicity of different species was obtained from the literature. Two different measures of the brightness and extent of coloration were used. (i) Twenty-four human observers were asked to rank different photos of each different species in the analysis in terms of contrast to a leaf-littered background. (ii) Color photos of each species were scanned into a computer and a computer program was used to obtain a measure of the contrast of the colors of each species relative to a leaf-littered background. Comparative analyses of the results were carried out with two different models of character evolution: gradual change, with branch lengths proportional to the amount of genetic change, and punctuational change, with all change being associated with speciation events. Comparative analysis using either method or model indicated a significant correlation between the evolution of toxicity and coloration across this family. These results are consistent with the hypothesis that coloration in this group is aposematic.

Iron, infection and the evolutionary ecology of heart disease

Levels of iron intake and stored iron have been implicated as risk factors for coronary heart disease. More recently, considerable interest has centered on the role of a variety of infectious pathogens, particulary bacterial pathogens, in the development of artherosclerosis and heart disease. The mechanism whereby elevated iron levels increase the risk of coronary heart disease is not well understood. Here it is proposed that the influence of iron levels on the persistence, pervasiveness and intensity of bacterial infections may play an important role in the development of coronary heart disease.

A phase II study to evaluate the combination of fludarabine, mitoxantrone and dexamethasone (FMD) in patients with follicular lymphoma

BACKGROUND

'Molecular response' is being investigated as a therapeutic goal in follicular lymphoma (FL). High response rates in FL with the fludarabine combination 'FMD' have been associated with 'molecular remission'. A phase II study of FMD in FL was therefore conducted.

PATIENTS AND METHODS

Fifty-four patients, ten of whom were newly diagnosed received FMD. Forty-four percent of the previously treated patients had 'chemoresistant' disease. Treatment comprised: fludarabine 25 mg/m2 days 1-3, mitoxantrone 10 mg/m2 day 1, and dexamethasone 20 mg days 1-5. Blood/bone marrow was collected for quantitation of t(14;18) by 'real-time' PCR.

RESULTS

The overall response rate was 37 of 54 (69%), complete responses being seen in 11 patients (20%), with no difference between newly diagnosed and the previously treated patients. However, the response rate in 'chemosensitive' relapse was 84% compared to 44% in patients in whom the last prior regimen had failed. Molecular responses were seen in 17 of 25 and PCR negativity in 8 of 25, although molecular and clinical responses did not always correlate. Toxicity was moderate, 19 patients required admission. However, in 6 of 12 patients, subsequent G-CSF mobilised stem cell harvests failed.

CONCLUSIONS

FMD was well tolerated but with a lower than expected response rate. Molecular responses were seen in the majority of responding patients however, 'molecular remission' was rare.

A UK multicentre phase II study of rituximab (chimaeric anti-CD20 monoclonal antibody) in patients with follicular lymphoma, with PCR monitoring of molecular response

Follicular lymphoma (FL) cells express CD20 and are associated in most cases with the t(14;18) chromosomal translocation. A multicentre study was undertaken between January 1997 and January 1998 to assess the complete response rate (CR) and overall response rate (RR) to rituximab, a chimaeric anti-CD20 monoclonal antibody. Seventy patients with previously treated FL received rituximab (375 mg/m2/week x4, by intravenous infusion). Restaging studies were performed 1 and 2 months after therapy. Molecular monitoring for the presence of cells harbouring the Bcl-2/JH gene rearrangement in the peripheral blood (PB) and bone marrow (BM) was performed before and after treatment using a two-step semi-nested polymerase chain reaction (PCR) assay. The overall RR was 32/70 (46%), being highest in patients who had received only one previous treatment (12/15, 80%). However, only two patients achieved a CR. The median duration of response was 11 months. Thirteen of 21 evaluable 'PCR-positive' patients (62%) became 'PCR-negative' in PB and/or BM samples 1 month after rituximab, although this did not correlate with clinical response. Treatment was generally well tolerated, although one patient developed Stevens-Johnson syndrome. Rituximab was shown to be active in FL, and in some cases PB and/or BM became PCR negative. Studies in combination with cytotoxic chemotherapy to increase the CR rate are warranted.

Visual mate choice in poison frogs

We investigated female mate choice on the basis of visual cues in two populations of Dendrobates pumilio, the strawberry poison frog, from the Bocas del Toro Archipelago in Panama, Central America. Mate choice experiments were carried out by presenting subject females of each of two morphs of this species (orange and green) from two different island populations (Nancy Key and Pope Island) with object frogs (one of each morph) under glass at one end of a terrarium. Recorded calls were played simultaneously from behind both object frogs. The experiments were carried out under two light regimes: (i) white light, and (ii) relatively monochromatic filtered blue light. Subject females from each population displayed a significant preference for their own morph under white light, but not under blue light. These results indicate that female D. pumilio use visual cues in mate choice, and suggest that colour may be the visual cue they use.

Cost-effectiveness of initial therapy with 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors to treat hypercholesterolemia in a primary care setting of a managed-care organization

From January 1994 through May 1995, Prudential HealthCare-North Texas prospectively studied 299 member patients diagnosed with hypercholesterolemia for whom pharmacotherapy with one of four 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors, also known as statins, was prescribed. The purpose of this study was to measure the relative cost-effectiveness (CE) of these drugs in a real-world setting. This study provides information to assist decision makers in managed-care organizations (MCO) in making formulary selections. The study used a prospective, randomized, balanced cohort design, examining patients who had been prescribed initial therapy with a statin drug as monotherapy. Costs (direct medical and indirect costs) and effectiveness (percent reduction in low-density lipoprotein cholesterol levels) were based on approximately the first 6 months of initial therapy. Both the MCO and patient perspectives were considered. In the base case, mean CE ratios were significantly lower for fluvastatin compared with lovastatin, pravastatin, and simvastatin from both the managed-care perspective and the patient perspective. Sensitivity analysis did not alter the CE conclusions, even under conditions of varying cost structures. Although differences were found in the effectiveness of lovastatin, pravastatin, and simvastatin measured in this study versus efficacy measured for these drugs in controlled clinical trials, sensitivity analysis suggests that these differences alone do not determine the superior CE of fluvastatin. Finally, this study supports the idea that well-designed formularies should consider drug CE (based on safety, effectiveness, and cost) and that integration of the pharmacy benefit management with other medical management is essential. These results provide evidence that fluvastatin may represent a more cost-effective formulary choice among statin products used for initial monotherapy of hypercholesterolemia.

Phenotypic and genetic divergence in three species of dart-poison frogs with contrasting parental behavior

Why some species exhibit remarkable variation among populations while closely related species are relatively uniform remains unclear. The strawberry dart-poison frog (Dendrobates pumillo) exhibits spectacular color and pattern polmorphism among populations in the Bocas del Toro archipelago of Panama. In contrast, two other sympatric species of dart-poison frog, Phyllobates lugubris and Minyobates sp., show little color or pattern variation among island populations. Here we demonstrate that the color and pattern variation among populations of D. pumilio is not matched by higher levels of mitochondrial DNA sequence divergence relative to P. lugubris or Minyobates sp. Thus, neutral divergence in allopatry is unlikely to have caused the geographical differences observed in D. pumilio. We suggest that strong sexual selection associated with female parental care in D. pumilio, which contrasts the male parental care of P. lugubris and Minyobates sp., may have driven divergence in coloration and pattern in D. pumilio.

Three retroviral sequences in amphibians are distinct from those in mammals and birds

We isolated and characterized three endogenous retroviral fragments from the dart-poison frog Dendrobates ventrimaculatus. These are the first retroviral sequences to be identified in amphibians, and consequently retroviruses have now been found in each of the five major vertebrate classes. Comparison of the amphibian retroviral fragments, termed DevI, DevII, and DevIII, with mammalian and avian isolates revealed significant differences between their nucleotide sequences. This suggested that they were only distantly related to the seven currently recognized retroviral genera. Additional analysis by phylogeny reconstruction showed that the amphibian retroviral fragments were approximately equally related to the Moloney leukemia-related viruses, the spumaviruses, and walleye dermal sarcoma virus. Hybridization experiments revealed that viruses closely related to DevI, DevII, and DevIII do not appear to be widespread in other vertebrates and that DevI, DevII, and DevIII are all present at high copy numbers within their amphibian hosts, typically at over 250 copies per genome. The viruses described here, along with two others which have recently been found in a fish and a reptile, indicate that there may be some major differences in the retroviruses harbored by different vertebrate classes. This suggests that further characterization of retroviruses of fish, reptiles, and amphibians will help in understanding the evolution of the whole retroviral family and may well lead to the discovery of retroviruses with novel biological properties.

Cholinesterase inhibitor effects on neurotransmitters in rat cortex in vivo

A microdialysis technique was used to investigate the effect of physostigmine (PHY) and heptylphysostigmine (HEP), administered systemically or locally, on the extracellular levels of acetyl-choline (ACh), norepinephrine, dopamine and 5-hydroxytryptamine in the cerebral cortex of the rat. Levels of these neurotransmitters in dialysates were assayed simultaneously with two different high pressure liquid chromatography systems. No cholinesterase inhibitor was added into the probe to increase detection of ACh after systemic administration. Cholinesterase inhibition and its relation to ACh levels were also studied. Systemic administration of two doses of cholinesterase inhibitor [PHY (30 and 300 micrograms/kg) and HEP (2 and 5 mg/kg)] produced a dose-dependent increase in ACh levels. Local perfusion of these drugs through the probe elicited a strong increase in extracellular ACh. HEP produced a longer lasting inhibition of cholinesterase and a more prolonged elevation of ACh in cerebral cortex than PHY. After systemic administration of PHY (both doses), we observed a significant increase of norepinephrine levels. This effect was weaker after HEP. Local administration through the probe did not modify norepinephrine concentration. Dopamine levels were also increased after systemic administration. ONly HEP perfused into the probe elicited a significant increase in extracellular dopamine. Systemic or local administration did not modify 5-hydroxytryptamine levels. These observations suggest a more favorable pharmacological profile for HEP as a potential drug for Alzheimer disease, as compared to PHY.

Factors affecting ACTH release from perifused equine anterior pituitary cells

The multifactorial control of ACTH is well established. We wished to establish and characterize an in-vitro perifusion system, using equine anterior pituitary cells and physiological concentrations of secretagogues, to investigate factors which affect the dynamics of ACTH secretion. Anterior pituitary tissue was divided for dispersion into cells with collagenase, trypsin or dispase, or by mechanical dispersion. After dispersal followed by 18-h incubation, cells were perifused and the ACTH response to 10-min pulses of arginine vasopressin (AVP; 100 nmol/l), corticotrophin-releasing hormone (CRH; 0.01 nmol/l), and AVP (100 nmol/l) plus CRH (0.01 nmol/l) determined. ACTH responses to these secretagogues were lower (P < 0.05) in cells prepared using the enzymes dispase and trypsin than with the enzyme collagenase. Cells prepared by mechanical methods were not responsive. Collagenase-prepared cells were used in subsequent experiments. In dose-response studies (10-min pulse length), a steep CRH-ACTH dose-response curve was obtained with the minimum effective concentration of CRH between 0.001 and 0.01 nmol/l, and a maximum effective concentration of 1.0 nmol/l. A less steep AVP-ACTH dose-response curve was obtained with a minimum effective concentration of AVP between 0.5 and 5 nmol/l, and no plateau in response up to 5000 nmol AVP/l. Increasing the incubation time between cell preparation and stimulation with AVP from 18 h to 90 h significantly (P < 0.01) increased the ACTH response. Repeated stimulation by AVP (100 nmol/l) or CRH (0.01 nmol/l) (5-min pulses every 30 min for 23 pulses) produced ACTH responses which decreased in an approximately exponential curve with time. When AVP and CRH were given at physiological concentrations, pulse lengths and pulse frequency, the ACTH response to repeated 1-min pulses of AVP, measured as height above basal secretion, was potentiated by the addition of CRH (1, 2.5, 5, 10 and 20 pmol/l) as a constant perifusion at all AVP concentrations tested (1 nmol AVP/l, P < 0.02; 10 nmol AVP/l, P < 0.0005; 25 nmol AVP/l, P < 0.0005). During the 1-min AVP pulse, the AVP concentration at the level of the cells was 30% of the expected concentration. Potentiation was increased both by increasing AVP concentration (P < 0.00005) and by increasing CRH concentration (P < 0.00005) up to 5 pmol CRH/l. The ACTH height response to repeated AVP stimulation significantly (P = 0.034) decreased with time, independent of CRH and AVP concentration. There was a significant (P = 0.014) decrease in ACTH response to CRH infusion with time, independent of CRH concentration.(ABSTRACT TRUNCATED AT 400 WORDS)

Polymorphism in a ferritin H gene from chromosome 6p

This paper addresses the question of whether abnormalities in ferritin expression in the iron storage disease hemochromatosis (HC) involve major deletions or alterations in regions containing the two ferritin H genes that lie near the disease locus on chromosome 6p. We present evidence from analyses of Southern blots that neither gene is deleted in hemochromatosis. We also describe a polymorphism in one of the genes that we have previously shown to be a processed pseudogene. This polymorphism does not correlate with the presence of HC. The PIC value for this polymorphism was calculated as 0.49.

Communicating an evolutionary diagnosis of disability to parents

Communicating a diagnosis of disability to parents, when the diagnosis and prognosis are unclear, is problematic. This is discussed in the light of information received from mothers of such children who attended a counselling and support group. It is concluded that dissatisfaction with diagnosis is not inevitable, if similar guidelines to those suggested for children with Down's syndrome are used. It is essential that parents are involved in management and feel they have something practical to do to help their children. Clinics must organize themselves to avoid swamping parents with information and to provide regular ongoing support.

Ranitidine--bolus or infusion prophylaxis for stress ulcer

Stress ulcer is a dangerous complication for the critically ill patient. Prophylaxis with antacids can undoubtedly reduce this risk, if gastric pH is maintained above 3.5. Histamine receptor antagonists may achieve this more conveniently. We have studied the effects of ranitidine, given either as 50-mg boluses every 6 h or as one of two infusion regimes (125 or 250 micrograms/kg.h), in controlling pH in critically ill patients on a ventilator. The percentage of samples with a pH less than 4 fell in all groups during therapy; while there was no significant difference between groups, pH control was achieved more rapidly in the bolus group. Infusion therapy with ranitidine is an attractive concept but a loading dose must be used. The presence of occult blood in the gastric juice did not correlate with pH and was not affected by ranitidine therapy.

A comparison of two ranitidine intravenous infusion regimens in critically ill patients

The effect of two ranitidine intravenous infusion regimens on intragastric pH was studied in 134 critically ill patients admitted to 15 intensive care units. Intragastric pH was determined hourly for 30 hours. Those patients whose intragastric acidity fell below pH 4.0 for 3 or more of the first 6 hours were considered 'at risk' of developing stress-related gastric lesions and randomized to receive a 50 mg bolus of ranitidine together with a continuous intravenous infusion of either 0.125 or 0.25 mg kg-1 h-1 ranitidine for 24 hours. The maximal elevation in intragastric pH was achieved within 12 hours. The median intragastric pH for the last 20 hours of the infusion period was 5.9 for the higher dose group and 5.6 for the lower dose group. The increase in intragastric pH achieved by the two dosage regimens did not differ significantly throughout the 24 hour period. Patients having two or more of five major risk factors (head injury, major trauma, sepsis, respiratory failure/insufficiency and major surgery) had better overall control of intragastric pH on the higher dose of ranitidine than those receiving the lower dose. The majority of intensive care patients are likely to receive satisfactory treatment with the lower dosage regimen that was tested (0.125 mg kg-1 h-1). Those with multiple risk factors may, however, require treatment with higher doses of ranitidine (0.25 mg kg-1 h-1).

Ranitidine and cimetidine in the healing of duodenal ulcer: meta-analysis of comparative clinical trials

All available ranitidine and cimetidine comparative trials in acute duodenal ulcer disease were examined: of the 44 trials, 36 favoured ranitidine, and there was an overall difference in ulcer healing of 7%. Further stratification enabled examination of trials with common attributes: the most frequent endoscopic assessment was at 4 weeks to compare ranitidine 150 mg twice daily with cimetidine 1 g day-1 or 400 mg b.d. Twenty of these trials had sufficient data to permit pooling. Ranitidine was favoured in 18/20 trials and in three the differences achieved statistical significance. Results of the trials were combined using meta-analysis to calculate differences in ulcer healing. Most studies had sample sizes that were insufficient to detect clinically-important differences; the power to detect a 20% difference was less than 80% in 15/20 trials, and for a 10% difference was less than 80% in all but one trial. Fifteen trials compared ranitidine 150 mg b.d. with cimetidine 1 g day-1: healing after 4 weeks therapy was overall 6% greater for ranitidine. This was statistically significant (P less than 0.05) and the combined total number of patients had a power of 83% to detect this difference. In five trials the dose of cimetidine used was 400 mg b.d.: the 12% difference in healing in favour of ranitidine 150 mg b.d. was statistically significant, and the combined trials had a power of 95% to detect this difference. Ranitidine 150 mg twice daily heals significantly more duodenal ulcers after 4 weeks of therapy than either cimetidine 400 mg b.d. or cimetidine 1 g day-1.

A single night time dose of ranitidine in the acute treatment of gastric ulcer: a European multicentre trial

Four hundred and twenty eight patients with endoscopically diagnosed gastric ulcers, randomly allocated to treatment with ranitidine 300 mg at night or ranitidine 150 mg twice daily, were evaluated in a double blind multicentre trial conducted in 10 European countries. After four weeks, complete ulcer healing was observed in 138 of 211 patients (65%) treated with ranitidine 300 mg nocte and in 155 of 217 patients (71%) receiving 150 mg bd. Cumulative healing rates at eight weeks were 90% and 93%, respectively. There was no statistically significant difference between the healing rates at either four or eight weeks. The treatment regimens were equally effective at rapidly reducing the incidence of ulcer related symptoms. Adverse events reported were minor and equally distributed between the two groups. The results of this trial show that 300 mg of ranitidine administered at night is an effective and safe alternative to the current twice daily regimen for the short term treatment of gastric ulcer.

A single nighttime dose of ranitidine 300 mg versus ranitidine 150 mg twice daily in the acute treatment of duodenal ulcer: a European multicenter trial

Six hundred and five patients with endoscopically diagnosed duodenal ulcer were randomly allocated to treatment with ranitidine 300 mg at night or ranitidine 150 mg twice daily in a prospective double-blind multicenter trial conducted in nine European countries. Endoscopy at 4 weeks showed complete ulcer healing in 246 of 301 patients (82%) treated with ranitidine 150 mg b.i.d. and 230 of 304 patients (76%) treated with ranitidine 300 mg at night. Cumulative healing rates at 8 weeks were 95 and 94% respectively. Both treatment regimens were equally effective at rapidly reducing the incidence of ulcer-related symptoms. Adverse events were few and consistent with those reported in previous studies with ranitidine 150 mg twice daily. The results of this trial indicate that a single nighttime dose of ranitidine is an effective and safe alternative to the twice daily regimen in the acute treatment of duodenal ulcer.