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Intestinal dysmotility is a prominent feature of chronic radiation enteropathy. This study addressed the question whether localized radiation enteropathy without anatomical obstruction influences stomach to cecum transit time. Male rats were orchiectomized and a loop of ileum was sutured to the inside of the scrotum. After 3 weeks postoperative recovery, the “scrotal hernia” containing the transposed intestine was irradiated with 18 twice-daily fractions of 2.8 Gy, or 9 daily fractions of 5.6 Gy orthovoltage X-rays. Control animals were operated and sham-irradiated. Stomach to cecum transit time was assessed 26 weeks after irradiation. A 1-ml bolus of barium suspension was administered by gavage and diagnostic X-ray films were obtained at 0,1, 2,2.5, 3, 3.5, and 4 hr. Transit time was defined as the time to the first X-ray that showed unequivocal contrast filling of the cecum. Normal range and day-to-day variability were assessed in normal, unoperated control rats. After completion of transit studies, the rats were euthanized, samples from shielded and irradiated intestine were procured, and radiation injury was assessed with a histopathological scoring system. Median stomach to cecum transit time in unoperated controls was 2.25 hr. The surgical procedure and aging did not significantly affect transit time. Transit time was significantly prolonged both in the 2.8 Gy × 18 group (P = 0.02) and in the 5.6 Gy × 9 group (P = 0.0001). The association between histopathologic radiation injury and transit time did not reach statistical significance. We conclude that non-obstructing radiation injury in the distal ileum significantly prolongs intestinal transit time and that small bowel follow-through with barium contrast may be used to assess radiation enteropathy in this animal model. © 1995 Wiley-Liss, Inc.

Background. Late normal tissue reactions generally are believed to be independent of treatment time. However, previous studies suggest a relationship between acute mucosal injury and development of intestinal obstruction and enterocutaneous fistula formation. Thus, the pathogenesis of late intestinal complications may be complex, and mucosal cell proliferation during treatment may be important. This study assessed the influence of overall radiation treatment time on development of intestinal injury and complications after localized fractionated irradiation of rat ilium. Methods. Ninety-four male rats underwent orchiectomy, and a loop of small intestine was transposed to the scrotum

Eighty μmol/kg of copper(II)2(3,5-diisopropylsalicylate)4(H2O)2 [Cu(II)2(3,5-DIPS)4] given subcutaneously (sc) to female mice 24 h before lethal (LD10030) irradiation was found to allow 58% survival. Subsequent studies using LD5030 irradiations revealed that 80 or 92% survival was obtained in female or male mice, respectively, when 20 μmol/kg was given 3 h before irradiation; 88–92% survival was achieved in female mice treated with 2.5, 5, or 10 μmol/kg 3 h after irradiation; and 75 or 95% of the male mice survived when they had been given 50 μmol/kg orally 24 or 4 h, respectively, before irradiation. Using LD5030 irradiations it was also found that administration of 280 μmol of Fe(III)-(3,5-DIPS)3(H2O)/kg led to 84% survival in male mice; 80 μmol of Mn(II)-(3,5-DIPS)2(H2O)/kg allowed 96 or 100% survival in male or female mice, respectively; and 60 μmol Zn(II)-(3,5-DIPS)2/kg achieved 95% survival in male mice. In addition, all of these complexes were found to have anti-convulsant activities suggesting possible protection against radiation-induced seizures. It is concluded that these essential metalloelement complexes have radiation-protection and radiation-recovery activities and that their use represents a physiological approach to preventing or perhaps predominantly facilitating recovery from radiation injury.

In the first-known application of its kind, shockwave lithotripsy and contact-solvent dissolution of large, calcified gallstone burdens were performed simultaneously with three chemical solvents, each tested separately in an in vitro model, with the combined effects on gallstone eradication examined. Two solvents, ethyl propionate and isopropyl acetate, were chosen for their solubilizing ability and potentially high level of patient safety. The third solvent, a 70%:30% mixture of methyl tert-butyl ether (MTBE) and dimethyl sulfoxide (DMSO), was chosen for its known ability to accelerate the dissolution of calcium-containing gallstones. All stones were matched for size, weight, and number. Gallstone lithotripsy performed in ethyl propionate was significantly more effective (P less than .02) in the production of fragments less than 2 mm when compared with bile; lithotripsy with isopropyl acetate and the MTBE/DMSO mixture showed no statistically significant effect. Biliary lithotripsy performed in an ethyl propionate medium may enhance gallstone dissolution and the production of small fragments (diameter less than 2 mm).

Purpose To determine what interaction and effect different cholesterol gallstone solvents have on catheters used for gallstone chemolysis. Materials and Methods Five types of catheters used for biliary procedures were chosen: polyethylene, Percuflex, silicone, Silitek, and polyurethane. The solvents chosen were methyl tert -butyl ether, ethyl propionate, isopropyl acetate, and N-propyl acetate. After incubation of the catheters in the solvents for 72 hours, they were air dried. Weight and area changes were determined for each catheter. Additionally, carbon-13 nuclear magnetic resonance (NMR) spectroscopy was performed for analysis of composition changes. Results Three catheters – silicone, Silitek, and polyurethane – showed changes in their physical characteristics that would make them less desirable for stone chemolysis. The silicone catheter showed changes in elastic texture as well as a marked weight reduction. The Silitek and polyurethane catheters had similar, but less dramatic changes. C-13 NMR analysis of collected solvents showed that commonly used plasticizers were leached out of some catheters. Conclusion These results suggest that all catheters are not suitable for use with all solvents. The choice of catheter should be made based on the solvent in use. The polyethylene catheter performed best under the conditions and endpoints used in this study.

Nearly 50% of all cancer patients receive therapeutic radiation during the course of their disease. The risk of late complications is the main dose-limiting factor in the delivery of radiation therapy. The small intestine, the major site of chronic radiation enteropathy, is also the principal organ of glutamine consumption. We therefore hypothesized that the provision of supplemental glutamine may have a protective effect on the development of chronic radiation enteropathy.This study evaluated the effects of supplemental oral glutamine on the development of chronic radiation (XRT) enteropathy. After scrotalization of a loop of small intestine, rats were randomized to receive 1 g/kg/day glutamine (GLN) or glycine (GLY) by gavage. After 2 days of prefeeding, rats were randomized to 1 of 4 groups: GLN + XRT (n = 10), GLY + XRT (n = 10), GLN only (n = 10), GLY only (n = 10). Twenty Gy was delivered to the scrotalized bowel in the GLN + XRT and GLY + XRT groups via a collimated beam. Gavage was continued for 10 days. Animals were then pair-fed chow. Rats were killed at 2 months postirradiation. Chronic radiation injury was assessed microscopically.Injury scores in GLN + XRT were similar to those of unirradiated bowel and significantly different from GLY + XRT (1.89 +/- 0.48 in XRT + GLN vs. 6.42 +/- 1.55 in the XRT + GLY, p0.01). Elevated Injury Scores in the XRT + GLY group correlated with gross thickening and fibrosis, a 10-fold decrease in gut GLN extraction (1.40 +/- 4.3% in GLY + XRT vs. 16.0 +/- 5.1% in GLN + XRT, p0.05), and a 30% decrease in glutathione content (2.46 +/- 0.19 and GLY + XRT vs. 3.17 +/- 0.17 GLN + XRT, p0.05).Provision of GLN during abdominal/pelvic XRT may prevent XRT injury and decrease the long-term complications of radiation enteropathy.

Many in modern medical practice now embrace percutaneous transluminal angioplasty as a valid and important treatment option for occlusive vascular disease, both in coronary and peripheral arterial systems (1). Despite excellent overall technical and clinical success rates, immediate and long-term failures pose a substantial problem for this minimally invasive therapy. Interventionalists have countered immediate complications and failures (eg, difficult to cross lesions, dissection, elastic recoil, acute thrombosis) with improved guide wires and balloons, variety of stents, and antithrombotic pharmacologic agents. Combating long-term failure, predominantly restenosis, remains more of a challenge. Results of the study performed by Krueger et al (2) reported in this issue of Radiology add important support for the use of endovascular irradiation (brachytherapy) to prevent vascular restenosis after percutaneous therapy. In a prospective controlled study, the researchers randomized thirty patients to receive endovascular irradiation with an iridium 192 source or a placebo after percutaneous transluminal angioplasty of femoropopliteal atherosclerotic lesions. As opposed to most other studies, Krueger et al treated only de novo atherosclerotic disease with percutaneous angioplasty without stent placement. Twenty-two patients at sixmonth and 12 patients at 1-year follow-up underwent arteriography. The irradiation group showed a statistically significant change in the degree of stenosis after angioplasty compared with the nonirradiation group at both 6 months ( 14.7% 20.8 vs 37.7% 27.3, respectively; P .001) and 12 months ( 9.5% 34.5 vs 45.5% 40.7, respectively; P .03). In other words, the lumen at the angioplasty site continued to enlarge in the irradiation group compared with an actual luminal decrease in the nonirradiation group. Complications were minimal but included one acute thrombosis in the irradiation group that was probably secondary to vessel injury during catheter manipulation. The authors did encounter restenosis outside the angioplasty site but within the irradiated segment of the vessel in three cases (not significantly different from the placebo segments). The authors also obtained and analyzed a variety of other clinical, imaging, and physiologic parameters, such as patient interviews, duplex ultrasonography, treadmill examinations, and ankle-brachial index. Most of these parameters showed a trend, though not statistically significant despite differences in restenosis rates, toward benefit in the irradiation group. The relatively small number of patients in this study may have made differences in the clinical outcome undetectable. These study findings compare favorably with brachytherapy results of the coronary circulation (most treating instent restenosis) and few other reports of irradiation during peripheral femoropopliteal interventions (3). Liermann et al (4) published an 84% patency rate at 7.5 years for irradiated peripheral arteries (nonrandomized study). Minar et al (5,6) initially reported less success with long femoropopliteal lesions (nonrandomized study) but recently documented a reduction in restenosis from 53.7% to 28.3% at 6 months in a prospective randomized study (mixture of de novo and restenotic lesions, limited angiographic follow-up). Waksman et al (7) reported a 17.2% restenosis rate at 6 months (angiographically) and 13.3% rate (clinically) at 12 months in the irradiated superficial femoral artery (nonrandomized study). One or both of two pathologic processes generally contribute to restenosis after endovascular therapy. Recurrent or progressive atherosclerotic disease may cause luminal occlusion commonly 1 or more years after intervention. Neointimal hyperplasia occurs sooner, frequently in less than 1 year, and can also lead to narrowing. The pathologic process of intimal cell proliferation, mediated and characterized by activation of blood agents such as platelets and by migration of smooth muscle cells in the media and adventitia to the luminal surface, probably represents an exuberant reaction to vessel injury (such as that from angioplasty). The localized accumulation of these cells and the complex matrix they produce lead to a compromise of the vessel lumen. Of the different strategies to limit neointimal hyperplasia, cellular suppression with ionizing radiation has shown promise both experimentally and in clinical trials. Human studies of the coronary and peripheral vascular systems have usually used endoluminal transcatheter delivery of a radiation source, either a beta (such as phosphorus 32 or samarium 153) or a gamma-ray (such as iridium 192) emitter (8,9). This technique, however, has limitations and drawbacks. The use of these highly radioactive sources may expose patients, operating physicians, and tech

1. 1. The effects of continuous gamma radiation on the viability of Trichomonas vaginalis (ATCC 30001) were assessed by a colony count technique. 2. 2. A triphasic survival curve showed an initial shoulder (DQ) of 3 Gy followed by three linear curves with D0 values of 34, 300, and 90 Gy. 3. 3. Sterilization of 106 cells/ml occurred from 1600 to 1800 Gy of radiation. 4. 4. Population growth, subsequent to radiation exposure of 17–100 Gy, showed an increased lag time followed by a faster rate of growth, compared with unirradiated cells. 5. 5. Trichomonas vaginalis is more sensitive to ionizing radiation than free-living protozoa and appears as radiosensitive as those parasitic protozoa examined in radioattenuation experiments.

Amplatz vena caval filters were inserted percutaneously in 30 patients. Radiologic and clinical follow-up was available in 24 patients (cavogram, CT, or sonography in 20 patients, plain abdominal radiographs in two, and lower extremity venograms in two). Clinical follow-up only was available in four patients, and autopsy reports were available in two patients without radiologic follow-up. The filter was inserted without difficulty in 29 (97%) of the patients. Complications after insertion included recurrent pulmonary embolism in two (7%) of 30, caval thrombosis in seven (23%) of 30, ipsilateral lower extremity deep venous thrombosis after placement of the filter in one (3%) of 30, caval penetration in two (10%) of 20, and caval stenosis in one (5%) of 20. No migration of the filter was noted. Our experience suggests that the Amplatz vena caval filter is easy to insert and adequately prevents recurrent pulmonary embolism but is associated with a relatively high rate of caval thrombosis.

Pathological consequences of human exposure to increasing doses of ionizing radiation: Hematopoietic, Gastrointestinal, and Central Nervous System syndromes, are rather well understood.1 Bone marrow aplasia and loss of immunocompetency with low (2 to 10 Gray) doses of irradiation, gastrointestinal ulceration and systemic infection with higher radiation doses, and loss of brain function with still higher doses account for the diminishing duration of survival following exposure to increasing doses of ionizing radiation.

Angioscopy was used during in situ saphenous vein bypass grafting in seven patients. We were able to visualize valve incision, immediately identify and correct incomplete valvulotomy, identify side branches as potential arteriovenous fistulas, and assess distal anastomotic integrity. We encountered no retained valve cusps after angioscopy, as verified by Doppler ultrasound and completion angiography. Angioscopy verified distal anastomotic integrity in all patients with distal vein grafts large enough to accept the angioscope. Angioscopy requires minimal time, is relatively easy to use, serves as an adjunct to Doppler ultrasound and completion angiography, and has future potential as a therapeutic tool. (J VASC SURG 1986;4:360-4.)

Biological effects from experimental ultrasound studies, such as chromosome aberrations and retardation of growth, have been recorded but mostly at levels far in excess of diagnostic intensity. The data surveyed in this review suggest that there is apparently little or no danger associated with diagnostic ultrasound exposure at clinical levels.

A guide for radiation biology program directors is presented, with an annotated bibliography.

The success rates and clinical effectiveness of percutaneous laser thermal angioplasty for obstruction of the distal superficial femoral or popliteal arteries were assessed. Laser thermal angioplasty was performed with the first commercially available laser system on 25 atherosclerotic vascular lesions in 20 lower extremities of 18 patients. Fifteen of the lesions were occlusions (average length, 5.6 +/- 3.1 cm), and 10 were high-grade stenoses (average length, 2.6 +/- 1.8 cm). Indication for angioplasty was claudication limiting life-style in 12 extremities and threatened limb loss in eight. All patients were treated with a 1.5- or 2.0-mm metal-capped optical fiber attached to a 14-W argon-ion laser. Balloon angioplasty was performed after laser recanalization in all successful cases. The patients were followed by Doppler ankle/brachial index and clinical evaluation. Laser thermal angioplasty was technically successful (vessel recanalization) in 18 (90%) of 20 of the cases. Fourteen (70%) of 20 extremities were successes by ankle/brachial index follow-up, while 15 (75%) of 20 remained clinically improved after an average follow-up of 7.8 +/- 5.3 months. Laser thermal angioplasty has a technical and clinical success rate that compares favorably with previous reports of balloon angioplasty. With proper patient selection, laser thermal angioplasty can reduce the difficulty of traversing lesions that are amenable to standard balloon angioplasty and increase the number of vascular lesions that can be treated percutaneously but could not be recanalized without the use of laser energy.

The rejoining of radiation-induced DNA breaks, characterized by 5′ termini, was measured by the polynucleotide kinase method. This method has potential clinical value because DNA damage can be measured for cells within solid tissue. Following irradiation of a human squamous-cell carcinoma, DNA rejoining occurred, but at a slower rate than observed for mammalian cells in culture. The results of the study indicate that cells within solid tumors, in situ, are able to repair at least some radiation-induced DNA damage. The importance of this type of repair to tumor response following therapeutic radiology is not known at present.

The influence of thymine starvation on the single-strand molecular weight of deoxyribonucleic acid (DNA) from Escherichia coli was determined by sedimentation through gradients of alkaline sucrose. Growth of cells for as long as 150 min in thymineless medium did not significantly reduce the molecular weight below the control value of 2.4 ± 0.3 × 10 8 daltons. Incubation of cells in thymineless medium after exposure to 500 ergs/mm 2 of ultraviolet light or 20 krad of 137 Cs gamma rays did not appear to block the rejoining of single-strand breaks associated with irradiation. Thus, DNA repair enzymes, presumably including DNA ligase, are not significantly inhibited by thymine starvation.

L cells irradiated while in growth medium or in a balanced salts solution showed a rapid appearance of DNA breaks characterized by 5′ phosphoryl termini. Following irradiation, the number of breaks quickly reached a maximum, after which they were rapidly repaired. Dinitrophenol, an inhibitor of aerobic oxidative phosphorylation, prevented the DNA breaks from appearing.

The repair of radiation induced DNA damage in some micro-organisms has been explained on the basis of the “cut-and-patch” hypothesis. This hypothesis postulates that radiation produces alteration of the DNA bond structure, nucleolytic enzymes convert the bond alterations into frank breaks, and then the breaks are repaired by an enzyme ( s ) which has properties similar to DNA polymerase. In this paper we give experimental and theoretical evidence to support the notion that the “cut-and-patch” mechanism very likely is responsible for the repair of radiation induced DNA damage in cultured mammalian cells.

Because of recent interest in the use of neutrons for radiotherapy, there has been an increased interest in the radiobiology of neutrons. In this irradiated cell study, a 1.3 MeV accelerator produced beam currents over 100 μA on the water-cooled 3-mm thick beryllium disk target. The monolayer of irradiated cells was neutron-shielded by about 700 kg of paraffin. The neutron energy spectrum for the 9Be(d,n)10B reaction was obtained, with an average neutron energy calculated to be between 3.3 and 3.5 MeV, and an average linear energy transfer calculated at more than 30 keV∕micron.

Copper(II)2(3,5-Diisopropylsalicylate)4(H20)2 has been found to have antiinflammatory, antiulcer, anticonvulsant, anticancer, anti-carcinogenic, antimutagenic, and radiation recovery activities and it prevents reperfusion injury. To study pharmacokinetic parameters accounting for these pharmacological effects the double labeled 67Cu(II)2(carboxy-14C-3,5-diisopropylsalicylate)4 complex was synthesized and used to obtain these parameters. Treatment of mice with 1 μmol of this complex revealed that 67Cu was distributed to blood, liver, kidney, intestine, lung, thymus, femur, muscle, spleen, brain, urine, and feces within 0.5 hr and patterned changes in 67Cu content of these tissues and excreta were found throughout the 96 hr term of this study.

Mouse L-929 cells were exposed in a monolayer to x rays and to a 3.5 MeV neutron beam for comparison of damage effects. Single dose experiments showed a radiobiological effectiveness of 1.5 for neutrons when compared to x rays. Both single and paired dose experiments indicated that the cells were unable to repair neutron-induced damage. Dinitrophenol was found to increase the survival of those cells irradiated with neutrons.

Intracellular adenosine triphosphate (ATP) levels were measured in both hypoxic and aerobic cultures of V79 Chinese hamster cells treated with 5-thio-D-glucose (5-SH-D-Glc). This glucose analog, a known inhibitor of D-glucose transport and metabolism, reduced ATP in cell cultures allowed to become hypoxic by cell metabolism, but not in aerobic cultures treated similarly. Cells depleted of ATP were unable to rejoin x-ray-induced deoxyribonucleic acid (DNA) strand breaks as measured by the alkaline surcrose gradient sedimentation technique. Results show that 5-SH-D-Glc leads to reduced energy metabolism in cells dependent on glycolysis for ATP production. The inference for radiation therapy is that inhibition glucose metabolism selectively depletes energy reserves in hypoxic cells, rendering these cells more radiosensitive and leading to a more effective tumor treatment.

Copper(II)(3,5-diisopropylsalicylate)2 (Cu-DIPS) provided substantial radioprotectant activity when administered 3 hours prior to exposure to gamma irradiation1. The present study investigated immune parameters of Cu-DIPS-mediated radioprotectant activity. It was found that Cu-DIPS did not prevent the destruction of mature lymphocytes, but accelerated the recovery of both the numbers of cells in the spleen and the responsiveness of those cells.

Atherosclerotic vascular disease is a major cause of morbidity and mortality throughout the world. Surgical and pharmacologic agents have been used in the treatment of this disease with varying degrees of success. Recently, angiographically guided balloon dilatation of atherosclerotic vascular lesions has gained widespread use and acceptance because of efficacy, decreased cost, and reduced patient morbidity and mortality. There are, however, some lesions which cannot successfully be treated by this method because of their location, size, or configuration.

Ionizing radiation of oxygenated aqueous solution is known to produce superoxide as a secondary product of radiation,1–3 Part of the cellular injuries caused by radiation can be attributed to the acute increase of superoxide. Addition of Cu-Zn superoxide dismutase (Cu-Zn SOD) to the extracellular medium can significantly protect cultured cells against radiation damage.4 Adding Cu-Zn SOD to cultures of myoblasts protected them from a radiation-induced decrease in viability and altered morphology5 as well as chromosomal damage.6

Our experience with angioscopy is presented elsewhere.1,2 Rather than review our laboratory and clinical data, we intend this discussion to serve as an exhortation toward the refinement of angioscopic technology. The following empirical observations and practical considerations are aimed at identifying the major weaknesses of, and providing direction for the future course of technical research in, the field of angioscopy.© (1984) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The cardiovascular applications of flexible fiber-optic technology are imminent because of recent advances in miniaturization. In the work described here, angioscopy, or vascular endoscopy, was performed in the cadaveric aorta and in the systemic and pulmonary circulations of the canine model and selected human patients. Subsequent to our development of percutaneous techniques, clinical trials have ranged from lower-extremity venoscopy to aortic-root arterioscopy. Angioscopy could be clinically useful because of relative or absolute contraindications to iodinated contrast material. The ability to see in color and three dimensions may afford some other advantages to angioscopy over conventional angiography.

Angiographically guided balloon dilatation of atherosclerotic vascular lesions is an established non-surgical technique for treating selected patients with occlusive vascular lesions. Balloon angioplasty involves compressing, stretching, and tearing of the arterial intima with subsequent reshaping and healing of the vessel lumen. The atherosclerotic lesion is mechanically displaced but otherwise remains intact. Totally occluding vascular lesions are not amenable to balloon dilatation unless the catheter can be advanced through the occlusion, a practice with inherent complications.

Copper (II) (3, 5-diisopropylsali cylate)2 (Cu-DIPS), administered to mice 3 hr prior to exposure to 8.0 Gy irradiation, increased the 42 day survival rate from 40% to 85%. Treatment with Cu-DIPS significantly accelerated spleen repopulation and the recovery of immune responsiveness following irradiation.2 In the present study the effects of Cu-DIPS on the recovery of hematopoietic activity in bone marrow and spleen following irradiation were investigated.

The relative biologic effectiveness (RBE) of fast neutrons in the production of single strand DNA breaks is 1.6 as compared to that of 250 kVp x rays. Monolayers of L-929 cells were treated with dinitrophenol during irradiation to prevent the DNA strands from rejoining; the extent of DNA damage was measured by the alkaline sucrose sedimentation method. The RBE for DNA damage is essentially the same as the RBE measured by cell survival methods.

Copper(II)(3,5-diisopropylsalicylate)2 (Cu-DIPS), administered subcutaneously to mice at 80 mg/kg body weight, had marked radioprotective activity. Given 3 h before exposure to 8.0 Gy (800 rad) irradiation, Cu-DIPS increased the 42-day survival from 40% to 86%. Seven days after exposure to 8.0 Gy, there were severe reductions in spleen weight (73%) and cellularity (98%) in both Cu-DIPS- and vehicle-treated mice. Viable spleen cells collected 7 days after irradiation were totally unresponsive to mitogenic or antigenic stimulation regardless of Cu-DIPS or vehicle treatment, suggesting that Cu-DIPS did not prevent radiation-induced damage to mature lymphocytes. At 14 days, when Cu-DIPS-treated mice started to show improved survival over vehicle-treated mice, spleen weights and cellularity were 2.5- and 3.5-fold higher, respectively, in Cu-DIPS-treated mice. Treatment with Cu-DIPS not only enhanced splenic repopulation, but also accelerated the reappearance of both B and T cell reactivities. Spleen cell responsiveness to the B cell mitogen, lipopolysaccharide (LPS), and the T cell mitogen, concanavalin A (Con A), regenerated significantly faster in Cu-DIPS-treated mice. Cu-DIPS also significantly accelerated the regeneration of T-dependent antibody induction. Based on these assays of immunocompetence, Cu-DIPS-treated mice had, on average, a seven-fold greater capacity to respond to immune stimulation than vehicle-treated mice 24 days after irradiation.

The formation of colonies in solid medium was used as a criterion of viability to determine the effect of ultraviolet radiation on Trichomonas vaginalis. Both viability (colony) counts and total cell (hemocytometer) counts were used to estimate physiological ages of cell populations to be irradiated. Washed-cell suspensions in 0.6% saline were exposed to far- (254 nm) and near-UV (300–400 nm) radiation and dose-response survival curves were constructed from colony counts. The effect of far-UV was found to be independent of growth phase with the D0 for exponential, early stationary, and late stationary cells 2.6, 2.7, and 2.7 J/m2, respectively. Survival to near-UV increased with the age of cells with the estimated D50 being 216 J/m2 for exponential cells, 1360 J/m2 for early stationary cells, and 4200 J/m2 for late stationary cells. Exponential cells of Trichomonas gallinae irradiated with near-UV had a D50 of 340 J/m2. T. vaginalis is highly sensitive to far-UV relative to protozoa. T. vaginalis and T. gallinae are highly sensitive to near-UV relative to other microorganisms.

Using the polynucleotide kinase method, we were able to demonstrate the repair of radiation induced DNA breaks in mouse liver DNA and in L cells. The specificity of the enzyme indicates the breaks to have 5′ phosphoryl termini.

In an earlier paper we attempted to show the “cut-and-patch” mechanism to be responsible for the repair of radiation induced DNA damage in cultured mammalian cells. The experimental basis was provided by survival studies. For the present investigation we used the polynucleotide kinase method to measure directly the appearance and rejoining of radiation induced DNA breaks characterized by 5′ PO 4 termini. A multicompartmental mathematical model was developed, and estimates of parameter values were made by experiments with L cells. The results suggest most of the frank DNA breaks following irradiation to be a consequence of endogenous nucleolytic processes and not due to the radiation, per se . Because of the massive cell killing which occurs in spite of preventing the appearance of DNA breaks, we postulate the existence of radiation induced DNA changes which (1) are not liable to endogenous nucleolytic processes and (2) cause cell lethality.

SummaryStarved L cells show a radiation-induced cyclic labeling of the acid-insoluble fraction when adenosine and deoxyadenosine are used as labeled precursors. The response consisted of a rapid uptake and loss of label. A similar effect has also been reported for 32P labeling of DNA.These findings support the idea that X-irradiation of mammalian cells produces increased action of an enzyme which rejoins single-strand breaks in DNA. The enzyme mechanism involves formation of a transient DNA-adenylate complex. In such a reaction, labeled adenylate should enter and then leave the DNA fraction. The results reported here agree with such a mechanism.

BECAUSE the repair of radiation injury would seem to consume energy, chiefly in the form of ATP, we have studied the response to radiation of L cells, severely depleted of intracellular ATP. We have found that 2,4-dinitrophenol (DNP) can reduce intracellular ATP by about 90 per cent, that L cells treated with DNP for up to 8 h lose none of their reproductive integrity and that treated cells are less sensitive to radiation, particularly at a high dose.

This paper reports the results of studies with a line of cultured rat sarcoma cells (RT-2 cells). Survival curves indicate the cells to be highly radioresistant [ $D_{0}=240\ \text{rads}$ (air) and $D_{0}=750$ rads (hypoxic)]. The RT-2 cells, originally derived from a hepatosarcoma, retain their malignant potential while in culture. Generation cycle analysis indicates a cell cycle duration of 21 hr; $G_{1}-10.7$ hr, S-8 hr, $G_{2}-1.5$ hr; M-0.8 hr. With the exception of its high radioresistance, the RT-2 cell responds to X-radiation in a manner similar to many other cultured mammalian cell lines.

Experiments with bacteria suggest that extensive DNA degradation is an important step in the repair of radiation injury. Because of the potential importance, similar experiments with cultured mammalian cells were performed. L cells prelabeled with ${}^{3}{\rm HTdR}$ were suspended in medium and irradiated with doses of 0, 100, 500, and 1000 rads of 250 kVp x-rays. The results showed: (a) No massive DNA degradation occurred during the first 6 postirradiation hours; (b) although a small amount of radioactivity is released into the suspending medium, this is not increased by increasing dose of radiation; (c) the release of the radioactivity occurred in the presence of 2,4-dinitrophenol-an uncoupler of aerobic oxidative phosphorylation; (d) most of the released radioactivity was in the form of thymidine; and (d) the intracellular concentrations of alkaline deoxyribonuclease and DNA polymerase were not increased after irradiation.

The uncoupler of aerobic oxidative phosphorylation, 2,4-dinitrophenol (DNP), has been previously shown to decrease the radiation sensitivity of L cells. In the present investigation we performed paired irradiation experiments with DNP-treated cells. Although DNP treatment virtually stops macromolecular synthesis, the paired-dose survival curve showed a definite "repair" segment. The absolute survival reached by the DNP-treated cells was greater than that in parallel irradiated control cells kept in complete growth medium.

The uncoupler of oxidative phosphorylation, 2,4-dinitrophenol (DNP) has been shown to decrease the radiosensitivity of L cells in spite of producing a severe depression of DNA, RNA, protein, and ATP synthesis. To further explore these findings, experiments were performed with other compounds which affect oxidative phosphorylation. These included studies with asynchronous L cells and with L cells synchronized by the double thymidine block technique. The results showed that two uncouplers of oxidative phosphorylation, arsenate and DNP, produced an increase in postirradiation survival. Two inhibitors of oxidative phosphorylation, azide and cyanide, although depressing macromolecular synthesis, caused no increase in postirradiation survival. Cyanide, in fact, produced a slight decrease in survival. Experiments with synchronized cells indicate that the effects of arsenate are chiefly exerted on cells in S phase, while the effects of DNP are distributed throughout the intermitotic interval.

Mouse L cells show a cyclic32 P labeling of DNA following relatively low doses of x-rays. This effect appeared for cells which had been starved or treated with 2,4-dinitrophenol (DNP) but not for cells irradiated in growth medium. The response consisted of a rapid uptake and loss of label. Changes in ATP metabolism paralleled the cyclic labeling of DNA. This behavior possibly explains the enhanced repair of radiation injury previously described for DNP treated cells.