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Biomedical subjects

P J O'Brien

Publications and source records attributed to P J O'Brien.

At least 253 records · Page 14Linked to original sources
PubMed1983

Effect of chrysotile asbestos and silica on the microsomal metabolism of benzo(a)pyrene.

The effects of chrysotile, water-leached chrysotile, and silica on microsomal metabolism of benzo(a)pyrene in vitro were studied. Examination of benzo(a)pyrene metabolites generated by 3-methylcholanthrene-pretreated rat liver microsomes, in the presence of chrysotile fibers, revealed a reduction in the overall metabolism of the hydrocarbon. Thus, chrysotile appeared to modify the activities of aryl hydrocarbon hydroxylase and epoxide hydrolase. Leaching chrysotile in deionized water for 24 hr elicited a similar response. Silica, in contrast to chrysotile, did not decrease the microsomal metabolism of benzo(a)pyrene. Chrysotile, as well as water-leached chrysotile, considerably diminished the microsomal production of water-soluble benzo(a)pyrene metabolites. Precoating the fibers with heparin or bovine serum albumin partially abolished this inhibition. The liver microsomal metabolism of benzo(a)pyrene in rats subjected to intraperitoneal administration of chrysotile was 58% of that in untreated rats.

Animals↗
PubMed1983

The La Trobe Twin Study: a genetic approach to the structure and development of cognition in twin children.

Twins are particularly useful for developmental behavior genetics, if adequate consideration is given to the possibilities of twin-singleton differences and of data from twins being unrepresentative of the entire population. As an alternative to existing analyses in the developmental behavior genetics of cognition, the covariance structure analysis method in biometrical genetics involving twins and other relatives has the potential for dissecting the determinants of the structure of cognitive abilities and how these change during childhood, as well as checking on the adequacy of twin data. Designed with these aims in mind, the La Trobe Twin Study is a mixed longitudinal analysis of 1,356 twins, their siblings, and cousins, who are followed between the ages of 3 and 15 years on a battery of physical and behavioral tests. The criteria for choosing behavioral tests in such a project are discussed, along with the comprehensive series of questionnaires necessary to examine the children's development in the context of the stresses a multiple birth may impose on a family. In discussion of methods of analysis, 2 points are emphasized: (1) Twin-singleton differences are specific to particular abilities rather than being general, and (2) the incidence of family changes and stresses in such that these should be considered among the environmental effects on development along with the more usual indices of family environment.

Adolescent↗
PubMed1982

Dislocations of the lower cervical spine.

In 34 cases of cervical spine facet dislocation treated between 1975 and 1979, the dislocations were reduced by closed methods and immobilized in the halo thoracic brace. If closed reduction was unsuccessful, open reduction and fusion were performed. There is a high incidence of failure of closed reduction and halo thoracic immobilization in patients with minimal or no neurologic deficit. Bilateral facet dislocation was more frequently associated with severe neurologic injury than was unilateral facet dislocation, Use of closed reduction is time consuming, often unsuccessful, and may result in neurologic deterioration. Patients with facet dislocations and minimal neurologic injury are at risk of late instability following halo thoracic brace immobilization, and therefore open reduction and posterior cervical fusion may be advisable for them. However, surgical fusion carries a high incidence of long-term neck pain and stiffness, and is indicated only in patients at risk of developing late instability.

Adolescent↗
PubMed1981

RCS rat macrophages exhibit normal ROS phagocytosis.

Peritoneal macrophages from RCS rats exhibit phagocytic capability equal to that found in macrophages from normal strains of rat. The similarity in phagocytic activity was found with rat or bovine rod outer segments as well as with dystrophic retinal debris. Thus the genetic defect in RCS pigment epithelium is not expressed in the macrophages, which are available to clear the debris layer that accumulates in dystrophic RCS retinas.

Animals↗
PubMed1980

Hydroxyl radical involvement in the luminol chemiluminescence from the reaction of arachidonic acid with sheep vesicular gland microsomes.

The luminol chemiluminescence associated with the reaction between vesicular gland microsomes and arachidonic acid was found to be inhibited by superoxide dismutase, catalase and hydroxyl radical scavengers. It was also found that diethylenetriamine pentaacetic acid caused only slight inhibition. This is interpreted as showing the formation of hydroxyl radicals in a Haber-Weiss reaction and the interaction of luminol with the hydroxyl radicals. The Haber-Weiss catalyst is taken to be heme iron as the luminescence was not inhibited by diethylenetriamine pentaacetic acid. A model system involving lipoxygenase, haematin and arachidonic acid was shown to be similar, the hydroxyl radicals coming from the interaction of haematin with the hydroperoxides, produced from the lipoxygenase-arachidonic acid reaction.

Animals↗
PubMed1980

Selenium-independent glutathione peroxidase activity in rabbit liver.

The reduction of linoleic acid hydroperoxide catalyzed by rat liver cytosol was previously shown to be catalyzed by a selenium-dependent glutathione peroxidase. In contrast, the activity in rabbit liver cytosol could also be attributed to a selenium-dependent peroxidase. The selenium-independent peroxidase copurified with glutathione transferase B and was completely inhibited by antitransferase B antiserum and transferase substrates. These results suggest that glutathione transferase B in rabbit liver cytosol is involved in the intracellular decomposition of lipid peroxide and could explain the lower selenium requirement of rabbits in comparison with other species.

Animals↗
PubMed1980

The role of ambient lighting in circadian disc shedding in the rod outer segment of the rat retina.

Rats raised from birth on a 7 A.M.:7 P.M. light cycle exhibited a circadian burst of shedding 1 1/2 hr after the scheduled onset of light. This rhythmic event persisted even after the animals had been placed in total darkness for up to 2 weeks. When animals were placed in constant light (LL) for more than 24 hr, the shedding peak was abolished. A period of darkness of at least 2 hr, ending at the normal time for light onset, was necessary for the production of a shedding burst. When animals were placed in altered lighting cycles, the shedding rhythm shifted accordingly, although the speed of this shift was greatest with large advances in the light cycle and slowest with small delays in the light cycle. Animals exposed to LL and then returned to the dark exhibited the original shedding rhythm, a phenomenon not affected when the optic nerves were severed. A shedding peak could be induced at a noncircadian time by exposing the animals to more than 20 hr of LL followed by 2 hr of darkness and 1 1/2 hr of light, although the magnitude of the shedding was related to the circadian time.

Animals↗
PubMed1980

Evidence for both local and central regulation of rat rod outer segment disc shedding.

Rats entrained to a 7 A.M.:7 P.M. lighting cycle had one eye patched and then were placed in either constant light or in a 2 A.M.:2 P.M. lighting cycle. In both cases, the patched eyes maintained the original pattern of rod outer segment (ROS) disc shedding, whereas the open eyes responded to the ambient lighting conditions. When the optic nerves were severed at the optic chiasm, the shedding rhythm persisted, but it was no longer possible to shift the rhythm to a new lighting cycle. From these experiments we conclude that ROS disc shedding is regulated both by local oscillators within the orbit as well as by central elements.

Animals↗