[en] X irradiation of the lens of a young rat with doses exceeding 2 Gy (200 rad) causes the fragmentation of the nuclei of some of the cells of the meridional rows (MR). The karyopyknosis, which seems to begin as a blebbing of the nucleus, is the result of a direct effect on the cells which were in the MR at the moment of irradiation. The numbers of fragmented nuclei, when observed at the peak time of 12 hr after irradiation, reveal a strong dose dependence. Four Gray will produce less than one such damaged nucleus in 10 rows while 24 Gy exposures result in one fragmented nucleus for every two rows. Time-course analysis revealed that the time of onset is inversely correlated to dose. Fragmented nuclei were observed 4.5 hr following 24 Gy and appeared only at the 9-hr interval following 6 Gy. From the first to the third day after irradiation, the numbers of fragmented nuclei per MR were independent of dose. The fact that the nonmitotic cells of the meridional rows are affected suggests that the pathology is one which has classically been described as interphase death. The details of these observations and a discussion of their role in the overall phenomenon of radiation cataractogenesis are presented

No abstract available

[en] Studies were conducted on the effect of age on the production of fragmented nuclei in meridional row (MR) cells following ocular exposure to x radiation. It was found that vulnerability to such damage is maximal approximately 4 weeks postpartum in rats, and that increasingly larger doses of x rays were required to produce equal responses in older animals. Studies on other animals (mice, rabbits, frogs) thought to be resistant to this injury indicate that the failure to see this pathological change in those species is related to age. Although its role in cataractogenesis is unclear, direct damage to the nuclei of MR cells may be ubiquitous among animals susceptible to radiation cataract development

[en] The effect of age on the development of radiation cataracts in rat lenses has been investigated using the Columbia--Sherman rat as an experiment model. A detailed pattern of age dependence was obtained at several different dose levels. In general at dose levels from 200 to 300 rads the lens changes occurred sooner and progressed faster in the adult lenses than in young lenses. In the dose range from 300 rads to 900 rads opacities developed sooner in the young lenses but progression was faster and severe opacities developed sooner in adult lenses. Above 900 rads opacities developed sooner and progressed faster in the young lenses. (U.S.)

[en] Plasma levels of 2-hydroxyestradiol (2-OHE₂) were measured using a new RIA procedure. Values were below the detection limit of the assay (<10 pg/ml), except in the third trimester of pregnancy, when they rose to approximately 15 pg/ml. The infusion of 130 μg/h purified 2-OHE₂ elevated its plasma concentration to 155 pg/ml, consistent with a plasma MCR (MCR/sub p) of approximately 20,000 liters/day. The infusion of [³H]2-OHE₂ to equilibrium and chromatographic separation of the extracted plasma metabolites yielded an MCR/sub p/ of about 13,000 liters/day; the major plasma metabolite comigrated with 2-methoxyestradiol, and [³H]delta-methoxyestrone was also formed. The MCR/sub p/ of 2-OHE₂ is approximately half that of 2-hydroxyestrone (2-OHE)₁, but much higher than those of other steroids. As is true for 2-OHE₁ the clearance of 2-OHE₂ must occur primarily in the blood compartment. Together, the measured MCR/sub p/ values and estrogen receptor affinities of 2-OHE₂ and 2-OHE₁ predict a relative potency for effects upon gonadotropin secretion which is close to that observed in vivo

[en] The effect of varying doses of accelerated (570 MeV/amu) argon ions on the rat lens is described with detailed observations on the sequence of development of the cataracts, the time-dose relationship, and the analysis of their cataractogenic potential. The relative biological effectiveness (RBE) of the heavy particles for cataract production, compared to low linear energy transfer (LET) radiation (X-rays), has been established. These data indicate that, as with neutrons, the RBE increases with decreasing dose and that at a dose of 0.05 Gy an RBE of about 40 was observed

[en] Studies were designed to assess the contribution of X-ray-induced intraocular inflammation to radiation cataractogenesis in the rat and the rabbit eye. In the rat it was observed that only X-ray doses exceeding 18 Gy produced ocular changes consistent with uveitis beginning 1-4 days post-irradiation. Low to moderate cataractogenic doses failed to produce such changes. In the rabbit eye a 10 Gy single dose of X-rays induced inflammation and cataract. The same dose when divided into ten 1 Gy daily fractions was non-inflammatory yet produced cataracts similar in appearance and time of onset to that induced by a single tenfold higher X-ray dose. These and additional studies using endotoxin-induced uveitis suggest that inflammation is not essential to the development of X-ray cataract. (author)

[en] Cataracts, produced in 4-week old rats using 185 kVp X-rays and 570 MeV/amμ charged Argon (Ar) nuclei, were studied by light and scanning electron microscopy (SEM) at varying intervals post-irradiation. The severity and extent of the damage varied as an increasing function of dose and correlated well with cataract stage. Damage was generally limited to the equatorial and posterior subcapsular regions. The late stage cataracts were associated with massive disruption of the equatorial region and the formation of a granular matrix which extended to the poles. Ultrastructural changes were noted also in the superficial cortical region, while the lenticular nucleus and the remainder of the cortex remained unchanged

[en] It has been postulated that high energy heavy ions cause a unique form of damage in living tissue, which results from the high linear energy transfer of accelerated single particles. We have searched for these single-particle effects, so-called microlesions, in composite electron micrographs of retinas of rats which had been irradiated with a dose of 1 Gy of 570 MeV/amu argon ions. The calculated rate of energy deposition of the radiation in the retina was about 100 keV/micron and the influence was four particles per 100 micron 2. Different areas of the irradiated retinas which combined would have been expected to be traversed by approximately 2400 particles were examined. We were unable to detect ultrastructural changes in the irradiated retinas distinct from those of controls. The spatial cellular densities of pigment epithelial and photoreceptor cells remained within the normal range when examined at 24 h and at 6 months after irradiation. These findings suggest that the retina is relatively resistant to heavy-ion irradiation and that under the experimental conditions the passage of high energy argon ions does not cause retinal microlesions that can be detected by ultrastructural analysis

[en] For a number of biological end points it has been shown that, in contrast to low linear energy transfer (LET) radiation, dose fractionation of high-LET radiation does not result in a reduction in overall effectiveness. Studies were conducted to determine the effect of fractionating the exposures to heavy ion doses on the development of cataracts. Rat eyes were exposed to single doses of 1, 5, and 25 cGy of 570 MeV/amu40Ar ions and to 2, 4, and 10 Gy of 250 kVp X rays. These were compared to unirradiated controls and eyes which were exposed to the same total dose delivered in four fractions over 12 h. While in all cases fractionation of the exposure to X rays produced significant reduction in cataractogenic potential, fractionating doses of 40Ar ions caused a dose- and stage-dependent enhancement in the development of cataracts