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G R Howells

Publications and source records attributed to G R Howells.

At least 19 recordsLinked to original sources
PubMed1982

Reduced resorption of cortical bone in mice with induced osteopetrosis.

Two groups of syngeneic radiation chimaeras were established, the reconstitution being with spleen from osteopetrotic mice on the one hand and normal bone marrow on the other. Induced osteopetrosis in the former was evident radiologically not only as metaphyseal opacity but as unduly dense cortices compared with the latter, particularly terminally after 16-18 months. The radiological impressions were confirmed by measurement of cortical thickness in both longitudinal and transverse sections of undecalcified femoral shafts. Measurements were made with a Quantimet-720 System-30 Image Analyser. Terminally the differences were highly significant. One concludes that defective osteoclasts of osteopetrotic mice derived from haematopoietic stem cells fail to resorb not only primitive woven bone but also cortical laminar bone.

Animals↗
PubMed1982

Relationship between blood flow, bone structure, and 239Pu deposition in the mouse skeleton.

The rate at which blood is supplied to several bones in female CBA mice was calculated from 18F measurements in bone and blood. Blood flow measurements were compared with plutonium uptake in whole bone and on endosteal and periosteal bone surfaces. The results showed that: (a) the rate at which blood is supplied to bone determines the rate of deposition of plutonium; (b) there is a threshold rate of blood supply below which plutonium is not deposited; and (c) the rate of blood supply determines the density of plutonium deposition on endosteal but not no periosteal bone surfaces. These results are discussed in the light of the current bone blood supply hypotheses.

Animals↗
PubMed1982

Dominant lethal and ovarian effects of plutonium-239 in female mice.

In two separate experiments (C3H x 101)F1 female mice were injected intravenously with 239Pu in trisodium citrate, then mated in pairs to strain CBA males, to test for dominant lethality. In the first experiment 10 muCi kg-1 and in the second 20 muCi kg-1 body mass was injected. Matings were after 6 days in the first experiment (estimated ovarian absorbed dose of 0.1 Gy) and after 3, 6 or 12 weeks in the second (estimated ovarian doses of 1.11, 2.45 and 5.91 Gy respectively). No evidence of dominant lethal induction was found in the first experiment, but in the second there was a significant increase over controls in pre-implantation loss in all three series. Post-implantation lethality increased significantly (by 12 per cent) only after 12 weeks' exposure. With the 6- and 12-week exposures (especially the latter) luteal counts fell and fewer females became pregnant than in controls. This is attributed to oocyte killing by the alpha-particles. Histological and autoradiographic investigations showed a marked reduction in ovarian size and follicular numbers with fission-tracks clustered mainly over the medullary stroma. The pre-implantation loss may stem from lowered fertilization of oocytes because of their damage, so that the best measure of dominant lethality is that based on post-implantation death. Thus there is only slight evidence for the induction of genetic damage, which is in line with previous findings after chronic exposures of female mice.

Animals↗
PubMed1982

Uranium in bone: metabolic and autoradiographic studies in the rat.

The distribution and retention of intravenously injected hexavalent uranium-233 in the skeleton of the female rat has been investigated using a variety of autoradiographic and radiochemical techniques. These showed that approximately one third of the injected uranium is deposited in the skeleton where it is retained with an initial biological half-time of approximately 40 days. The studies also showed that: 1 Uranium is initially deposited onto all types of bone surface, but preferentially onto those that are accreting. 2 Uranium is deposited in the calcifying zones of skeletal cartilage. 3 Bone accretion results in the burial of surface deposits of uranium. 4 Bone resorption causes the removal of uranium from surfaces. 5 Resorbed uranium is not retained by osteoclasts and macrophages in the bone marrow. 6 Uranium removed from bone surfaces enters the bloodstream where most is either redeposited in bone or excreted via the kidneys. 7 The recycling of resorbed uranium within the skeleton tends to produce a uniform level of uranium contamination throughout mineralized bone. These results are taken to indicate that uranium deposition in bone shares characteristics in common with both the 'volume-seeking radionuclides' typified by the alkaline earth elements and with the 'bone surface-seeking radionuclides' typified by plutonium.

Animals↗
PubMed1981

A semi-automated technique for assessing the microdistribution of 239 Pu deposited in bone.

A semi-automated analytical procedure is described for the localisation of 239 Pu in bone. The method is based on the use of a Quantimet 720B Image Analyser for the analysis of neutron-induced autoradiographs, and may be applied to most tissues with fissionable radionuclides. Compared with former methods the present technique offers improvements in accuracy and a considerable saving on time and manpower. These savings arise mainly from the ability of the Quantimet to be used for the automatic detection of the fission-fragment tracks and to operate directly on the neutron-induced autoradiograph without recourse to photography. Results are presented for the distribution of 239 Pu in the ilia of CBA mice at 24 h post-injection.

Animals↗
PubMed1981

Morphometric studies on mouse bone using a computer-based image-analysis system.

The morphological structure of the ilium, femur, third lumbar vertebra and a central caudal vertebra of the female CBA mouse has been studied using 5 micrometer thick, plastic embedded, transverse and longitudinal sections. The sections were analysed on a Quantimet 720, system 30, image analyser connected on-line to a PDP11 computer. Separate endosteal and periosteal surface to volume ratios were calculated for each position of sampling in each bone. For this calculation the anisotrophy of the bone was estimated from measurements of mean chord lengths in longitudinal sections of the bone using a new analytical technique. Chord length distributions in transverse sections of bone were also measured and the relevance of such measurements to the study of morphological changes in the bone and its included marrow are briefly discussed.

Animals↗
PubMed1981

Improvements in histological techniques for epoxy-resin embedded bone specimens.

A procedure is presented in which some of the processing difficulties with fixation, embedding and cutting whole mouse bones and large bone pieces from other species are considered. The bone specimens are fixed in acetone or by a Karnovsky-formol-saline process which preserves intact endosteal surface-to-cortex layers. After fixation the bones are embedded in a hard mixture of epoxy resin to provide blocks with face sizes up to 3.5 x 3.0 cm. Mineralized sections are cut to 4 micrometer; demineralized at 3 micrometer. Sections are fastened to gelatin-subbed slides with pressure plates which produce flat, secure sections. After removal of the plastic, an unmodified Mayer's hematoxylin and a polychromatic eosin staining method is applied to demineralized sections, and a slightly modified method to mineralized sections.

Animals↗
PubMed1980

Comparative effects of protracted exposures to 60Co gamma-radiation and 239Pu alpha-radiation on breeding performance in female mice..

Breeding performances are compared of hybrid female mice given 239Pu (5 or 10 mu Cikg-1 body mass in 1% trisodium citrate via the tail-vein), or kept in a 10 rad/day or 20 rad/day 60Co gamma-irradiation field (but mated in the control area), or unirradiated. Ovarian dose-rates from the injected plutonium were initially 0.8 and 1.7 rad/day, changing little thereafter; actual gamma-ray dose-rates to breeding females averaged around 8 and 16 rad/day respectively. Both gamma-ray treatments affected reproductive performance more than the plutonium injections, with respet to duration of fertility and to offspring per litter in successive 4-weekly periods, though overall mean litter-sizes were not significantly less than controls. The r.b.e. for these effects on reproduction, attributed to germ-cell killing, is about 2.5 for the alpha-particles vs. gamma-rays, lower than for testis mass reduction in males. This low r.b.e. may be connected with inhomogeneity of alpha-particle dose within the ovary, but it is known that fission neutron versus gamma r.b.e.'s for impairment of female fertility are also lower than those for impairment of male fertility.

Alpha Particles↗
PubMed1979

Quantitative microscopic studies of the distribution and retention of 239Pu in the ilium of the female CBA mouse.

Three month old female CBA mice were injected with 50 nCi kg-1 body mass of minimally polymeric 239Pu-citrate and killed at 24 hours, 10 days, 1 month and 3 months after injection. The distribution of 239Pu in the ilia of these mice was analysed using neutron-induced autoradiography of bone sections together with computer-based methods of data reduction. Results of these investigations demonstrate that while 239Pu is initially localized on bone surfaces, by 3 months after injection it is fairly uniformly distributed throughout mineral bone and its included marrow.

Animals↗
PubMed1979

Plutonium in the tissues of foetal, neonatal and suckling mice after Pu-administration to their dams.

Twelve-week-old female (C3H x 101)F1 mice were injected intravenously with an ultrafiltered solution of 239Pu in per cent trisodium citrate, and mated to uninjected PCT males. The plutonium content was examined radiochemically and autoradiographically in placentae and foetuses on the 12th and 18th days of gestation, and in neonates during the 24 hours after birth and also at 18 days postnatally. Plutonium was distributed in most tissues of the late foetus and the suckling as it is in adult mice. However, on both the 12th and 18th days of gestation the concentration in the yolk-sac splanchnopleure was much higher than in any other foetal tissue. The amount of 239Pu in 18-day-old sucklings was between two and seven times as great as in 1-day-old neonates because of ingestion of milk from the lactating dams. In the first litter following administration of the radionuclide to the dam, about 0.02 per cent of the plutonium injected was transferred to an individual offspring by the time of birth, and a further 0.08 per cent by the time of weaning.

Animals↗
PubMed1978

Plutonium-239 deposition in the skeleton of the mouse.

Using the technique of neutron-induced autoradiography, together with computer-based methods of data reduction, the distribution of intravenously injected plutonium-239 in the skeleton of the female CBA mouse, 24 hours after injection, has been investigated. With these techniques, it is possible to measure the localization of 239Pu on the endosteal and periosteal surfaces of the bone to an accuracy of approximately +/- 2 x 5 micrometer. Results are reported for the distribution of 239Pu in the third lumbar vertebra, a central caudal vertebra, the right ilium and the right femur. Radiochemical analyses of the 239Pu in other comparable bones of the skeleton are also reported.

Animals↗