Healthy but smaller herds: Predators reduce pathogen transmission in an amphibian assemblage

Predators and pathogens are fundamental components of ecological communities that have the potential to influence each other via their interactions with victims and to initiate density- and trait-mediated effects, including trophic cascades. Despite this, experimental tests of the healthy herds hypothesis, wherein predators influence pathogen transmission, are rare. Moreover, no studies have separated effects mediated by density vs. traits. Using a semi-natural mesocosm experiment, we investigated the interactive effects of predatory dragonfly larvae (caged or lethal [free-ranging]) and a viral pathogen, ranavirus, on larval amphibians (grey treefrogs and northern leopard frogs). We determined the influence of predators on ranavirus transmission and the relative importance of density- and trait-mediated effects on observed patterns. Lethal predators reduced ranavirus infection prevalence by 57%-83% compared to no-predator and caged-predator treatments. The healthy herds effect was more strongly associated with reductions in tadpole density than behavioural responses to predators. We also assessed whether ranavirus altered the responses of tadpoles to predators. In the absence of virus, tadpoles reduced activity levels and developed deeper tails in the presence of predators. However, there was no evidence that virus presence or infection altered responses to predators. Finally, we compared the magnitude of trophic cascades initiated by individual and combined natural enemies. Lethal predators initiated a trophic cascade by reducing tadpole density, but caged predators and ranavirus did not. The absence of a virus-induced trophic cascade is ostensibly the consequence of limited virus-induced mortality and the ability of infected individuals to continue interacting within the community. Our results provide support for the healthy herds hypothesis in amphibian communities. We uniquely demonstrate that density-mediated effects of predators outweigh trait-mediated effects in driving this pattern. Moreover, this study was one of the first to directly compare trophic cascades caused by predators and pathogens. Our results underscore the importance of examining the interactions between predators and pathogens in ecology.

Inter‐ and intralaboratory variation of in vitro diffusion cell measurements: An international multicenter study using quasi‐standardized methods and materials

In vitro measurements of skin absorption are an increasingly important aspect of regulatory studies, product support claims, and formulation screening. However, such measurements are significantly affected by skin variability. The purpose of this study was to determine inter- and intralaboratory variation in diffusion cell measurements caused by factors other than skin. This was attained through the use of an artificial (silicone rubber) rate-limiting membrane and the provision of materials including a standard penetrant, methyl paraben (MP), and a minimally prescriptive protocol to each of the 18 participating laboratories. "Standardized" calculations of MP flux were determined from the data submitted by each laboratory by applying a predefined mathematical model. This was deemed necessary to eliminate any interlaboratory variation caused by different methods of flux calculations. Average fluxes of MP calculated and reported by each laboratory (60 +/- 27 microg cm(-2) h(-1), n = 25, range 27-101) were in agreement with the standardized calculations of MP flux (60 +/- 21 microg cm(-2) h(-1), range 19-120). The coefficient of variation between laboratories was approximately 35% and was manifest as a fourfold difference between the lowest and highest average flux values and a sixfold difference between the lowest and highest individual flux values. Intralaboratory variation was lower, averaging 10% for five individuals using the same equipment within a single laboratory. Further studies should be performed to clarify the exact components responsible for nonskin-related variability in diffusion cell measurements. It is clear that further developments of in vitro methodologies for measuring skin absorption are required.

Solvent Content and Macroviscosity Effects on the in vitro Transcutaneous Delivery and Skin Distribution of Ketoprofen from Simple Gel Formulations

The effects of decreasing solvent content and macroviscosity of simple topical gel formulations on the transcutaneous delivery and distribution of ketoprofen through skin were studied. Simple topical gels, based on ketoprofen, PEG 400 and either Cabosil M-5 or hydroxypropylcellulose were formulated and applied to freshly excised pig ear skin in vitro. Receptor phase samples were taken to determine permeation and depth profiles of ketoprofen were constructed, following tape stripping and membrane separation. Reduction of solvent from the Cabosil-thickened gels resulted in a rank order reduction in the permeation and distribution of ketoprofen. Reduced amounts of ketoprofen were distributed through the skin, particularly the dermis, with decreasing solvent. Two gels sharing the same macroviscosity exhibited significantly different skin permeation and distribution characteristics. The rank order reduction in both permeation and distribution of ketoprofen was attributed to the physiochemical properties of the formulation and how they may change after application, in particular the increased adsorptivity of ketoprofen to the Cabosil relative to the amount of solvent present in the system. This effect appeared to be predominant over any interactions occurring between the formulation and the skin. The data provided further evidence that adsorption to the thickener, rather than changes in viscosity, were primarily responsible for reduced permeation and distribution in the system examined.

Influence of estrogen and osteopenia/osteoporosis on clinical periodontitis in postmenopausal women

BACKGROUND

In Western societies, more than one-third of the female population above age 65 suffers from signs and symptoms of osteoporosis, a disorder characterized by low bone mass. Estrogen deficiency is the dominant pathogenic factor for osteoporosis in women. The impact of estrogen deficiency and osteopenia/osteoporosis on periodontitis is unclear, partially due to the lack of longitudinal studies evaluating clinical signs of gingival inflammation and periodontitis progression. The purpose of this investigation was to analyze prospectively the influence of serum estradiol levels and osteopenia/osteoporosis on common clinical measurements of periodontal disease over a 2-year period.

METHODS

Fifty-nine moderate/advanced adult periodontitis patients and 16 non-periodontitis subjects, all within 5 years after menopause at baseline, completed the study. Serum estradiol levels (E2) were measured yearly by 125I radioimmunoassay, and osteopenia/osteoporosis was determined by dual energy x-ray absorptiometry of the lumbar spine. Posterior interproximal clinical measurements were obtained every 6 months for the periodontitis patients, including explorer-detectable supragingival plaque, bleeding on probing (BOP) and relative clinical attachment level (RCAL). Baseline probing depths, smoking history, and demographic data also were collected.

RESULTS

Data indicated that baseline demographic measurements and bone mineral density (BMD) of the lumbar spine were not different between E2-deficient and E2-sufficient subjects. Smoking activity (packs smoked/day, years smoked) was higher in periodontitis patients (P=0.0001). E2-sufficient periodontitis subjects had a higher frequency of supragingival plaque without increasing gingival inflammation. E2 status did not influence the percentage of sites losing RCAL for either periodontitis or non-periodontitis groups, but when non-smoking osteopenic/osteoporotic periodontitis patients were evaluated, E2-deficient subjects had more BOP (43.8% versus 24.4%, P<0.04) and a trend toward a higher frequency of > or =2.0 mm RCAL loss (3.8% versus 1.2%, P<0.1) than E2-sufficient subjects.

CONCLUSIONS

These data suggest that E2 supplementation (serum E2>40 pg/ml) is associated with reduced gingival inflammation and a reduced frequency of clinical attachment loss in osteopenic/osteoporotic women in early menopause.

The use of 2 bioabsorbable barrier membranes in the treatment of interproximal intrabony periodontal defects

BACKGROUND

The use of barrier membranes in the treatment of periodontal defects is well documented. There has been an increase in the use of bioabsorbable materials which do not require a second surgical procedure for removal. However, there are little data evaluating the efficacy of bioabsorbable membranes in the treatment of intrabony defects. The purpose of this investigation was to evaluate the regenerative potential of 2 bioabsorbable barrier membranes without the use of grafting materials in the treatment of interdental intrabony defects.

METHODS

Twenty-three 2- or 3-walled intrabony defects were treated in 19 patients with a mean age of 50.4 years. All had completed nonsurgical treatment and a period of supportive periodontal therapy. The sites were randomly chosen to receive a barrier membrane composed of type I bovine collagen (11) or a copolymer of polylactic acid (PGA/PLA;12). A pressure sensitive disc probe was used to evaluate the following criteria at baseline and re-entry: 1) occlusal surface to the apical depth of probe penetration (OS-DP); 2) occlusal surface to the gingival margin (OS-GM); 3) occlusal surface to the alveolar crest (OS-AC); and 4) occlusal surface to the base of the osseous defect (OS-BD). Full thickness mucoperiosteal flaps were reflected to expose the surgical sites. The defects were debrided of the granulomatous tissue, the root surfaces instrumented and conditioned with 4 one-minute applications of 50 mg/ml of tetracycline. The barrier membranes were adapted to cover the defects and the flaps replaced. The postsurgical healing was uneventful and similar in both treatment modalities.

RESULTS

Twenty-three sites were surgically re-entered 6 months from the time of the initial surgery. The deepest probe depth for each site was used for statistical analysis. There was a mean relative attachment gain of 2.58+/-1.90 mm for the collagen, and 2.77+/-2.13 mm for the copolymer. There was a decrease in probing depth of 3.27+/-1.91 mm and 0.69+/-1.35 mm of recession for the collagen. The PGA/PLA copolymer had 3.55+/-2.47 mm reduction in probe depth and 0.78+/-1.14 mm of recession.

CONCLUSIONS

The data indicated the bioabsorbable collagen and copolymer membranes resulted in comparable results. A larger sample size would be necessary to determine if one membrane was superior to the other.

Complications associated with diabetes mellitus after guided tissue regeneration: case report

Dental practitioners need to be aware of the complications that can arise in the management and treatment of patients with diabetes mellitus. Patients with diabetes, and patients with a family history of diabetes, are at-risk dental patients. They are more likely to develop periodontal disease, and the periodontitis is more likely to be severe. Diabetes influences the progression and severity of periodontitis through changes in the small blood vessels, decreased collagen formation, and impairment of the host's defense mechanisms. Furthermore, complications associated with diabetes, such as impaired wound healing, can affect the patient's response to periodontal therapies like guided tissue regeneration (GTR). The case report in this article discusses the postsurgical complications that occurred during GTR treatment of a patient with non-insulin-dependent diabetes. The diabetic's susceptibility to periodontal disease and impaired wound healing can affect the progression of the disease and its treatment. Dental patients with diabetes require close supervision and frequent monitoring of their medical and dental health by the dental clinician.

L-arginine improves endothelium-dependent vasodilation in hypercholesterolemic humans

Endothelium-dependent vasodilation is impaired in hypercholesterolemia, even before the development of atherosclerosis. The purpose of this study was to determine whether infusion of L-arginine, the precursor of the endothelium-derived relaxing factor, nitric oxide, improves endothelium-dependent vasodilation in hypercholesterolemic humans. Vascular reactivity was measured in the forearm resistance vessels of 11 normal subjects (serum LDL cholesterol = 2.76 +/- 0.10 mmol/liter) and 14 age-matched patients with hypercholesterolemia (serum LDL cholesterol = 4.65 +/- 0.36 mmol/liter, P < 0.05). The vasodilative response to the endothelium-dependent vasodilator, methacholine chloride, was depressed in the hypercholesterolemic group, whereas endothelium-independent vasodilation, induced by nitroprusside, was similar in each group. Intravenous administration of L-arginine augmented the forearm blood flow response to methacholine in the hypercholesterolemic individuals, but not in the normal subjects. L-arginine did not alter the effect of nitroprusside in either group. D-arginine had no effect on forearm vascular reactivity in either group. It is concluded that endothelium-dependent vasodilation is impaired in hypercholesterolemic humans. This abnormality can be improved acutely by administration of L-arginine, possibly by increasing the synthesis of endothelium-derived relaxing factor.

Measuring physician mental workload: reliability and validity assessment of a brief instrument

This study examined the reliability and validity of a brief six-item instrument to measure the mental workload experienced by residents for specific patient visits to an ambulatory care clinic. Participating in the study were twenty-two residents in postgraduate years 1 through 3 who were working in the general outpatient clinic of an inner city, private, nonprofit community hospital. Cronbach's alpha coefficient for the instrument was 0.80. Findings supported several theory-based hypotheses on determinants and performance consequences of mental workload. Mental workload was positively correlated with fatigue (r = 0.42, P = 0.03) and inversely correlated with residents' self-rated experience with patients' problems (r = -0.65, P less than 0.001). Residents' performance was measured through self-ratings and faculty physicians' ratings. Mental workload was inversely correlated with self-rated performance (r = -0.67, P less than 0.001). The correlation of mental workload with faculty physician ratings that reflected the technical dimension of patient care (physician examination, medications, and procedures) was r = -0.38 (P = 0.04). With mental workload squared, the correlation was r = -0.45 (P = 0.02) and the form of the relationship, consistent with the hypothesis, was a slightly downward sloping curve. Limitations of this research are discussed as well as suggestions for further research.

Impaired vasodilation of forearm resistance vessels in hypercholesterolemic humans

The effect of hypercholesterolemia on vascular function was studied in humans. To eliminate the potential confounding effects of atherosclerosis, vascular reactivity was measured in the forearm resistance vessels of 11 normal subjects (serum LDL cholesterol = 111 +/- 7 mg/dl) and 13 patients with hypercholesterolemia (serum LDL cholesterol = 211 +/- 19 mg/dl, P less than 0.05). Each subject received intrabrachial artery infusions of methacholine, which releases endothelium-derived relaxant factor, and nitroprusside which directly stimulates guanylate cyclase in vascular smooth muscle. Maximal vasodilatory potential was determined during reactive hyperemia. Vasoconstrictive responsiveness was examined during intra-arterial phenylephrine infusion. Forearm blood flow was determined by venous occlusion plethysmography. Basal forearm blood flow in normal and hypercholesterolemic subjects was comparable. Similarly, reactive hyperemic blood flow did not differ between the two groups. In contrast, the maximal forearm blood flow response to methacholine in hypercholesterolemic subjects was less than that observed in normal subjects. In addition, the forearm blood flow response to nitroprusside was less in hypercholesterolemic subjects. There was no difference in the forearm vasoconstrictive response to phenylephrine in the two groups. Thus, the vasodilator responses to methacholine and nitroprusside were blunted in patients with hypercholesterolemia. We conclude that in humans with hypercholesterolemia, there is a decreased effect of nitrovasodilators, including endothelium-derived relaxing factor, on the vascular smooth muscle of resistance vessels.

Effects of alpha- and beta-adrenergic antagonists on plasma apolipoproteins and forearm blood flow in patients with mild hypertension

To study the mechanisms by which adrenergic antagonists affect blood pressure and plasma lipid levels, the effects of alpha-blockade with prazosin were compared with those of beta-blockade with propranolol in 23 normolipidemic, mildly hypertensive patients. Plasma lipoprotein composition, apolipoproteins, and some of the processes involved in lipid synthesis and clearance from plasma were investigated also. Patients entered an eight-week placebo period during which they were free of all antihypertensive medications. They were then randomly assigned under double-blind conditions to treatment with either prazosin (mean dose, 5 mg per day) or propranolol (mean dose, 133 mg per day) for eight weeks. Doses of both drugs were titrated to achieve either a decrease in diastolic blood pressure of 10 mm Hg or more or a reduction of diastolic blood pressure to less than 85 mm Hg, whichever was lower. Total plasma cholesterol decreased by 9 percent during prazosin treatment and increased by 7 percent during propranolol treatment (p less than 0.005 between treatments). Low-density lipoprotein cholesterol decreased by 12 percent with prazosin and increased by 12 percent with propranolol (p less than 0.005). Apolipoprotein B decreased by 17 percent with prazosin and increased by 15 percent with propranolol (p less than 0.005). There were no significant changes in total high-density lipoprotein cholesterol, its subfractions high-density lipoprotein2 or high-density lipoprotein3, or in apolipoprotein A1 and apolipoprotein A2. Plasma very low-density lipoprotein and low-density lipoprotein triglycerides were not significantly affected by either treatment. Plasma post-heparin lipase activities, which clear triglyceride and high-density lipoprotein cholesterol from plasma, were not altered significantly. Since regional blood flow could affect the clearance of plasma lipoproteins, measurements were taken of forearm blood flow, forearm vascular resistance, and maximal forearm vasodilatory potential during reactive hyperemia. The adrenergic antagonists had no effect on these measurements, nor did they affect cellular cholesterol synthesis as measured by the activity of 3-hydroxy-3-methylglutaryl coenzyme A reductase in blood mononuclear cells. The results of this study demonstrate differing actions between alpha- and beta-adrenergic antagonism. Alpha-blockade produced significantly lower levels of plasma low-density lipoprotein cholesterol and apolipoprotein B than beta-adrenergic antagonism without changes in high-density lipoproteins.