Radiation dose from reentrant electrons

In estimating the crew exposures during an extra vehicular activity (EVA), the contribution of reentrant electrons has always been neglected. Although the flux of these electrons is small compared to the flux of trapped electrons, their energy spectrum extends to several GeV compared to about 7 MeV for trapped electrons. This is also true of splash electrons. Using the measured reentrant electron energy spectra, it is shown that the dose contribution of these electrons to the blood forming organs (BFO) is more that 10 times greater than that from the trapped electrons. The calculations also show that the dose-depth response is a very slowly changing function of depth, and thus adding reasonable amounts of additional shielding would not significantly lower the dose to BFO.

Langerhans cell histiocytosis: central nervous system involvement treated successfully with 2-chlorodeoxyadenosine

A case of disseminated Langerhans cell histiocytosis with resistant central nervous system (CNS) disease in an adolescent is described. The child presented with visible cranial lesions, emesis, headaches, and short-term memory loss. Diagnostic evaluation revealed multiple osseous lesions in the cranium, ribs, vertebral bodies, and pelvis. The clinical course with complications and response to each therapy are sequentially reviewed. Remission, as evidenced clinically and by magnetic resonance imaging, was ultimately accomplished with 2-chlorodeoxyadenosine (2-CDA). The full course of 2-CDA was not tolerated due to bone marrow suppression. CNS histiocytosis is known to be resistant to therapy. Earlier introduction of 2-CDA for CNS disease might offer more successful treatment with less toxicity than seen in patient.

Uncoupling of intestinal mitochondrial oxidative phosphorylation and inhibition of cyclooxygenase are required for the development of NSAID-enteropathy in the rat

BACKGROUND

The pathogenesis of NSAID-induced gastrointestinal damage is believed to involve a nonprostaglandin dependent effect as well as prostaglandin dependent effects. One suggestion is that the nonprostaglandin mechanism involves uncoupling of mitochondrial oxidative phosphorylation.

AIMS

To assess the role of uncoupling of mitochondrial oxidative phosphorylation in the pathogenesis of small intestinal damage in the rat.

METHODS

We compared key pathophysiologic events in the small bowel following (i) dinitrophenol, an uncoupling agent (ii) parenteral aspirin, to inhibit cyclooxygenase without causing a 'topical' effect and (iii) the two together, using (iv) indomethacin as a positive control.

RESULTS

Dinitrophenol altered intestinal mitochondrial morphology, increased intestinal permeability and caused inflammation without affecting gastric permeability or intestinal prostanoid levels. Parenteral aspirin decreased mucosal prostanoids without affecting intestinal mitochondria in vivo, gastric or intestinal permeability. Aspirin caused no inflammation or ulcers. When dinitrophenol and aspirin were given together the changes in intestinal mitochondrial morphology, permeability, inflammation and prostanoid levels and the macro- and microscopic appearances of intestinal ulcers were similar to indomethacin.

CONCLUSIONS

These studies allow dissociation of the contribution and consequences of uncoupling of mitochondrial oxidative phosphorylation and cyclooxygenase inhibition in the pathophysiology of NSAID enteropathy. While uncoupling of enterocyte mitochondrial oxidative phosphorylation leads to increased intestinal permeability and low grade inflammation, concurrent decreases in mucosal prostanoids appear to be important in the development of ulcers.