Plasma xanthine oxidase activity in patients with adult respiratory distress syndrome

Oxygen metabolites have been implicated in the pathogenesis of various types of acute tissue injury. One biologic source of oxygen metabolites is the reaction catalyzed by the enzyme xanthine oxidase. Because we previously demonstrated that the substrates for xanthine oxidase (hypoxanthine and xanthine) are elevated in the plasma of critically ill patients, we questioned whether the enzyme itself might also be present. We therefore measured hypoxanthine concentration and xanthine oxidase activity in the plasma of 15 patients with ARDS and in 13 non-ARDS critically ill patients. Plasma xanthine oxidase activity in our ARDS group (1,514 +/- 975 mlU/L, mean +/- SE) was higher than that seen in the non-ARDS group (17 +/- 4 mlU/L, P [pre] .05). Plasma hypoxanthine was elevated in both groups, and there was no difference between the ARDS and non-ARDS groups (22.0 +/- 9.2 [mu]mol/L and 11.8 +/- 4.3 [mu]mol/L, respectively). The presence of both circulating xanthine oxidase and its substrate demonstrates the potential for intravascular oxygen metabolite production. These toxic products may then cause tissue injury in ARDS.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/26777/1/0000333.pd

Absence of xanthine oxidase or xanthine dehydrogenase in the rabbit myocardium

We directly measured the activity of the enzymes xanthine oxidase and xanthine dehydrogenase in rabbit and rat hearts, using a sensitive radio-chemical assay. Neither xanthine oxidase activity nor xanthine dehydrogenase activity was detected in the rabbit heart. In the rat heart, xanthine oxidase activity was 9.1 [plus-or-minus sign] 0.5 mIU per gram wet weight and xanthine dehydrogenase activity was 53.0 [plus-or-minus sign] 1.9 mIU per gram wet weight. These results argue against the involvement of the xanthine oxidase/xanthine dehydrogenase system as a mechanism of tissue injury in the rabbit heart, and suggest that the ability of allopurinol to protect the rabbit heart against hypoxic or ischemic damage must be due to a mechanism other than inhibition of these enzymes.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/25939/1/0000001.pd

Crop pests and predators exhibit inconsistent responses to surrounding landscape composition

The idea that noncrop habitat enhances pest control and represents a win–win opportunity to conserve biodiversity and bolster yields has emerged as an agroecological paradigm. However, while noncrop habitat in landscapes surrounding farms sometimes benefits pest predators, natural enemy responses remain heterogeneous across studies and effects on pests are inconclusive. The observed heterogeneity in species responses to noncrop habitat may be biological in origin or could result from variation in how habitat and biocontrol are measured. Here, we use a pest-control database encompassing 132 studies and 6,759 sites worldwide to model natural enemy and pest abundances, predation rates, and crop damage as a function of landscape composition. Our results showed that although landscape composition explained significant variation within studies, pest and enemy abundances, predation rates, crop damage, and yields each exhibited different responses across studies, sometimes increasing and sometimes decreasing in landscapes with more noncrop habitat but overall showing no consistent trend. Thus, models that used landscape-composition variables to predict pest-control dynamics demonstrated little potential to explain variation across studies, though prediction did improve when comparing studies with similar crop and landscape features. Overall, our work shows that surrounding noncrop habitat does not consistently improve pest management, meaning habitat conservation may bolster production in some systems and depress yields in others. Future efforts to develop tools that inform farmers when habitat conservation truly represents a win–win would benefit from increased understanding of how landscape effects are modulated by local farm management and the biology of pests and their enemies