The effects of gamma-irradiation on migration and survival of Schistosoma mansoni schistosomula in mice

Infections with irradiated Schistosoma mansoni were established by intramuscular (i.m.) injection of mechanically transformed schistosomula. A dose of 2.3 krad. allowed persistence of a small proportion of worms to adulthood, and of these survivors the majority of the female worms were sexually sterile. However, a small proportion of 2.3 krad.-irradiated females and a larger proportion of similarly irradiated males were capable of pairing successfully with non-irradiated partners. Radiation in the range 2.3 to 10 krad. resulted in slightly reduced peak recoveries from the lungs while 20 krad. resulted in a much reduced and 40 krad. a virtual absence of survival to the lung stage. Increasing doses of radiation in the range 2.3 to 10 krad. resulted in successively fewer parasites reaching the liver. Thus, the major sites of the radiation-induced mortality appeared to be as follows: 2.3 krad., mainly in the liver; 4 krad., in the lungs and liver; 10 krad., mainly in the lungs; 20 krad., at the injection site and in the lungs and 40 krad., mainly at the injection site. The infections studied here showed reduced survival following exposure to high doses of radiation compared with the infections, established as percutaneously applied cercariae, which have been reported by other workers. Possible reasons for the disparity are discussed.     

Effects of gamma radiation on spermatophore production and reception and subsequent fecundity and egg viability inAcarus siro L. (Acari: Acaridae)

Gamma radiation at doses higher than 10 krad significantly lowered the fecundity of the grain mite,Acarus siro. The fecundity of irradiated females was inversely correlated with dose, both when control or irradiated males were used in the pairing.Irradiation with ionizing radiation affected sexual activity of males. At doses above 10 krad the number of formed or observed spermatophores was lowered significantly.Sexual attractiveness of irradiated and control females to irradiated males was similar. However, non-irradiated males were observed mating more often with non-irradiated than with irradiated females.No correlation was found between the numbers of spermatophores present in the spermathecae of the female and the fecundity of the female. Irradiation had a greater effect on fecundity of the female than on sexual activity of the male; it did not affect the shape or behavior of spermatophores in the spermathecae of the female.Viability of eggs laid by females decreased by at least 50% when females or males were irradiated with doses above 20 krad. Irradiation also affected the survival of adults, but females were more sensitive than males. Net sterility index indicates that doses higher than 20 krad induce more than 90% sterility.     

Mass rearing history negatively affects mating success of male Anastrepha ludens (Diptera: Tephritidae) reared for sterile insect technique programs

Mating competitiveness and sterility induction into cohorts of wild Anastrepha ludens (Loew) (Diptera: Tephritidae) was compared among wild and laboratory flies reared for use in the sterile insect technique Mexican program. Laboratory flies stemming from an 11-yr-old bisexual strain were either not irradiated, irradiated at 3 krad (low dose), or irradiated at 8 krad. In 30 by 30 by 30-cm Plexiglas cages, where a cohort of laboratory flies (male and female) irradiated at different doses (0, 3, and 8 krad) was introduced with a cohort of wild flies, males and females of each type mated randomly among themselves. Compared with nonirradiated laboratory and wild males, irradiated males, irrespective of dose (3 or 8 krad), induced shorter refractory periods and greater mating frequency in wild females. Nevertheless, laboratory flies irradiated at a low dose induced greater sterility into cohorts of wild flies than laboratory flies irradiated at a high dose. In a 3 by 3 by 3-m walk-in cage, wild males gained significantly more matings with wild females than nonirradiated and irradiated laboratory males a finding that revealed a strong effect of strain on mating performance. Mating incompatibility of the laboratory strain might have obscured the effect of reduced irradiation doses on male mating performance in the walk-in cage. Our results highlight an urgent need to replace the A. ludens strain currently used by the Mexican fruit fly eradication campaign and at least suggest that reducing irradiation doses result in an increase in sterility induction in wild populations.     

Respiration and nutrition of radiation-sterilized female Dacus cucumis (Diptera: Tephritidae)

The oxygen consumption of flies irradiated with between 10 kilorads (krad) and 80 krad was not demonstrably different between doses, or when compared with untreated controls.Carbohydrate intake and initial body weights of irradiated flies were less than normal flies. However, the 10 krad irradiated flies accumulated a greater volume of fat body than normal flies, presumably because of failure of vitellogenesis in the former. Accumulation of fat body by 40 krad flies was initially retarded compared with 10 krad flies, but they later accumulated fat body at the same rate as the 10 krad flies. It is suggested that this was due to an initial hormonal disturbance caused by the higher dose.No degenerative changes were noted in the midgut of the 10 krad or 40 krad flies. The protein intake of these flies was similar to that of normal flies.

---

Zusammenfassung Einige Autoren haben wahrscheinlich machen können, daß sterilisierende Strahlendosen bei einigen Insektengruppen den Stoffwechsel beeinflussen. Jedoch sind für die Dipteren wenig Beweise für solche durch Bestrahlung hervorgerufene Störungen veröffentlicht worden. Die in dieser Arbeit beschriebenen Versuche waren darauf gerichtet, die Einflüsse der Bestrahlung auf einige physiologische Systeme von weiblichen Dacus cucumis zu bestimmen.Auf den Sauerstoffverbrauch konnte eine Wirkung von Strahlendosen von 80 Kilorad (krad) nicht festgestellt werden.Beim Vergleich von unbestrahlten Fliegen mit solchen, die 10 oder 40 krad erhalten haben, wurde gefunden, daß in beiden Fällen die bestrahlten Tiere zunächst weniger als normale wogen, daß aber später die Wachstumsrate der bestrahlten Fliegen anstieg, so daß ihr Gewicht sich schließlich dem der normalen anglich.Der Verbrauch von Eiweißlösung durch mit 10 und 40 krad bestrahlten Fliegen war dem der normalen ähnlich. Jedoch verbrauchten die bestrahlten Fliegen eine geringere Menge Zuckerlösung als die normalen. Es wird angenommen, daß darin der Ausfall des Kohlenhydratbedarfs durch die sterilen Ovarien zum Ausdruck kommt.Die mit 10 krad bestrahlten Fliegen bildeten ein größeres Fettkörpervolumen als die normalen. Es wird vermutet, daß dies eine kombinierte Folge der Nicht-Auflösung des pupalen und des gesteigerten. Aufbaus des adulten Fettkörpers bei Ausschaltung funktionierender Ovarien darstellt.Der Aufbau des Fettkörpers war anfänglich bei den mit 40 krad bestrahlten Fliegen gegenüber den mit 10 krad bestrahlten gehemmt, aber nach einer Verzögerung war die Zuwachsrate den mit 10 krad bestrahlten ähnlich. Es wird angenommen, daß das auf einer anfänglichen Hormonstörung bei den mit 40 krad bestrahlten Fliegen beruhen konnte.

     

East coast fever: 60Co-irradiation of Theileria parva in its tick vector, Rhipicephalus appendiculatus

Three experiments were carried out in which Theileria parva was irradiated in its tick vector, Rhipicephalus appendiculatus. In the first experiment, infected unfed adult ticks were irradiated at doubling doses from 4 to 32 krad. Some of the ticks were then fed for 4, 5, 6, 7 and 8 days on rabbits, and the parasites in their salivary glands examined. Five male and 5 female ticks from each irradiation dose were put onto each of a pair of susceptible cattle, whose reactions were recorded. Increasing doses of irradiation resulted in progressive destruction of the parasites. All cattle receiving ticks irradiated at doses up to and including 16 krad died of East Coast fever (ECF), and one of the cattle receiving ticks irradiated at 32 krad died.In the second experiment, recently engorged nymphs were irradiated at 1, 2 or 4 krad, and moulting nymphs at doses of 2, 4, 8, 12, 16 or 32 krad. The salivary glands of the resultant adult ticks were examined after the ticks had fed for 4, 5, 6, 7 or 8 days on rabbits. Engorged nymphs irradiated at 4 krad failed to moult, whilst moulting nymphs irradiated at 32 krad moulted but failed to attach to rabbits. Doses of irradiation survived by the ticks had no apparent morphological effect on the parasites they contained.In the third experiment, infected unfed adult ticks were irradiated at 0, 5, 10, 15, 20 25 30, 35, 40, 45, 50 or 60 krad. The ticks were fed on rabbits for 5, 6 or 7 days. Some of them were then examined morphologically, whilst others were ground in MEM/BPA and aliquots of the supernatant used to inoculate groups of 5 cattle. The reaction of these cattle, together with the morphological examination of the parasites, suggested that increasing doses of irradiation destroyed increasing numbers of parasites.     

Immunization of zebu calves against Fasciola gigantica, using irradiated metacercariae

The pathogenesis of unirradiated, 3 krad-irradiated and 20 krad-irradiated metacercarial infections was compared in zebu calves studied over a 10-week period. Calves exposed to 1000 unirradiated metacercariae (mc) became hypoalbuminaemic, and showed elevated serum concentrations of liver enzymes, whereas neither of the other groups was significantly affected. At slaughter, a mean of 332 flukes was recovered from the 0 krad group, while only 23% and 12% of this number were recovered from the 3 krad and and 20 krad groups, respectively. All the worms recovered from the 20 krad group were stunted, and found in biliary ductules, but a mean of 13% of the flukes recovered from the 3 krad group were large, and dwelling in main bile-ducts. Liver lesions typical of acute fascioliasis were present in the 0 krad group, but lesions in the other groups, and particularly the 20 krad group, were far less severe. Judged on clinico-pathological criteria, a single vaccination of calves with 1000 3 krad-irradiated mc induced partial resistance to a challenge with 1000 normal mc eight weeks later, but the reduction in worm recovery was not statistically significant. There was less evidence of protection when two vaccinating doses of 3 krad mc were given within four weeks, with challenge at week 8, and a single vaccination was ineffective against a challenge four weeks later. However, when the irradiation dose was increased to 20 krad, a hgh level of resistance (69% worm reduction) was induced by a single vaccination, given eight weeks before challenge, and liver pathology was strikingly reduced in the vaccinated animals.     

Control of the circadian rhythm of locomotor activity in the house cricket

A detailed analysis was made of the locomotor activity of Acheta domesticus under conditions of 12 hr light and 12 hr darkness (LD 12 : 12) and of continuous darkness (DD). Under LD 12 : 12 it was found that there are three types of insects: (1) those beginning the period of increased locomotor activity immediately after darkness falls, (2) considerably before this time, and (3) considerably after this time. Under DD conditions the greater amount of the insects have a free-running rhythm shorter than 24 hr, while only a small percentage have a rhythm of more than 24 hr.Destruction of the neurosecretory cells of the pars intercerebralis by means of radio waves leads to the formation of hyperactivity and loss of locomotor activity rhythm when more than half of these cells are destroyed.Injection of reserpine into the insect's haemolymph with doses of 10 μg/g of body weight results in a reduction in locomotor activity and produces arrhythmicity for 2 to 3 days under LD 12 : 12 conditions. Under DD conditions, however, this same dose results in a total and irretrievable loss of free-running rhythm. Histological studies of the brain of crickets following injection of reserpine show a large degree of accumulation of neurosecretion in the cells of the pars intercerebralis as compared with control insects.A hypothesis is put forward as to the way in which the brain centres regulating locomotor rhythm act in crickets.     

Development of resistance to coccidiosis in the absence of merogonic development using X-irradiated Eimeria acervulina oocysts

Sporulated oocysts of the protozoan Eimeria acervulina were subjected to 0, 10, 15, 20, or 30 krad of X-irradiation and inoculated into susceptible outbred chickens to determine if radioattenuated coccidia could induce protection against parasite challenge. Irradiation treatment had an appreciable dose-dependent effect on parasite development. Insignificant numbers of oocysts were produced by chickens inoculated with parasites that had been exposed to greater than 10 krad X-irradiation. Sporozoites exposed to 15 or 20 krad irradiation conferred significant protection against the appearance of intestinal lesions after parasite challenge. Sporozoites subjected to the highest dose level (30 krad) did not produce any significant level of protection. To investigate this phenomenon further and assess intracellular parasite development, susceptible outbred strains of chickens were administered either nonirradiated (0 krad) oocysts or oocysts that were exposed to an optimal dose (15 krad) or a high dose (30 krad) of X-irradiation. Immunofluorescence staining of tissue sections from each treatment group at various intervals after the initial administration of irradiated parasites indicated that sporozoites exposed to 15 krad irradiation were as capable of invading the host intestinal epithelium as nonirradiated sporozoites. However, at 48, 60, 72, and 96 hr, there was a marked reduction in merogonic development in groups receiving irradiated sporozoites compared to those inoculated with nonirradiated parasites. The latter parasites underwent profuse merogonic development; in contrast, irradiated parasites demonstrated little (15 krad) or no (30 krad) merogonic development. These results suggest that induction of a protective immune response occurs during a critical period early in intracellular development of E. acervulina.     

An evaluation of the Drosophila zeste somatic eye mutation test for the detection of genotoxic azo dyes and an aromatic amine

The rate of DNA synthesis was studied in normal cell strain and in strains from patients suffering from inherited disorder ataxia telangiectasia (AT). After exposure to reactively low doses of oxic X-rays (0–4 krad) DNA synthesis was depressed in AT cell strains to a significantly lesser extent than in normal cells. This response was observed in both an “excision-deficient” and an “excision-proficient” strain. In contrast, there was no difference in DNA-synthesis inhibition between AT and normal cells after UV exposure. After X-irradiation of cells from patients with xeroderma pigmentosum, both complementation group A and XP variants, the observed rate of DNA synthesis was equal to that in normal cells. An exception was the strain XP3BR which has been shown to be X-ray sensitive. This strain exhibited diminished DNA synthesis inhibition after X-ray doses below 1 krad.These data suggest a relationship between hypersensitivity to X-rays and diminished depression of DNA synthesis.     

Locomotor Activity Rhythm in the Field Mouse Mus booduga Phase-shifts to Melatonin Injections in a Dose-dependent Manner

Melatonin is known to shift the phase of the locomotor activity rhythm in the field mouse Mus booduga in accordance with a type-I phase response curve (PRC), with phase delays during the subjective day and phase advances during late subjective night and the early subjective day. At CT4 (circadian time 4; i.e. 16 hr. after activity onset) and CT22 of the circadian cycle, a single dose of melatonin (1 mg/kg) is known to evoke maximum delay and maximum advance phase-shifts, respectively. We investigated the dose-dependent responses of the circadian pacemaker of these mice to a single dose of melatonin at the times for maximum delay and maximum advance. The circadian pacemaker responsible for the locomotor activity rhythm in these mice responded to various doses of melatonin in a dose-dependent manner with the magnitude of phase shifts increasing with dose.     

Effects of testosterone on the behavior of male cynomolgus monkeys (Macaca fascicularis)

To determine the threshold doses of testosterone propionate (TP) that cause clear-cut behavioral changes in the sexual behavior of castrated male cynomolgus monkeys, observations were made on three males during successive 5-week treatment periods while they received daily subcutaneous doses of 100 μg TP increasing in octaves to 25.6 mg TP. Males were tested with each of the same two ovariectomized, estrogen-treated females (6 pairs, 330 1-hr behavior tests). To mimic the diurnal plasma testosterone rhythm, TP injections were given at 1600 hr and blood samples were obtained at 0800 hr (141 samples). Male ejaculatory activity increased at the threshold dose of 200 μg TP per day giving plasma testosterone levels of 830 ng/100 ml, which is in the physiological range of 600–1600 ng/100 ml for intact males. This threshold dose was eight times higher than in rhesus monkeys on a dose per kilogram body weight basis. There was a further marked increase in ejaculatory performance at higher doses (6.4 to 25.6 mg) giving supraphysiological plasma levels of 4000–9000 ng/100 ml. There were individual differences in the behavioral changes occurring with TP treatment, and the female partner modulated the effects. These findings were generally similar to those obtained with male rhesus monkeys, but certain species differences were noted.     

Locomotor Activity Rhythm in the Field Mouse Mus booduga Phase-shifts to Melatonin Injections in a Dose-dependent Manner

Melatonin is known to shift the phase of the locomotor activity rhythm in the field mouse Mus booduga in accordance with a type-I phase response curve (PRC), with phase delays during the subjective day and phase advances during late subjective night and the early subjective day. At CT4 (circadian time 4; i.e. 16 hr. after activity onset) and CT22 of the circadian cycle, a single dose of melatonin (1 mg/kg) is known to evoke maximum delay and maximum advance phase-shifts, respectively. We investigated the dose-dependent responses of the circadian pacemaker of these mice to a single dose of melatonin at the times for maximum delay and maximum advance. The circadian pacemaker responsible for the locomotor activity rhythm in these mice responded to various doses of melatonin in a dose-dependent manner with the magnitude of phase shifts increasing with dose.     

Dose-dependent cytokinetic changes following 1-beta-D-arabinofuranosylcytosine and hydroxyurea in L1210 and S-180 in vivo.

DNA synthesis inhibition and recovery in L1210 and S-180 ascites tumors following 1-beta-D-arabinofuranosylcytosine (Ara-C) and hydroxyurea (HU) were measured autoradiographically as a basis for optimizing drug schedules. Tumor bearing mice, 10(6) cells day 0, were treated on day 4 with 20, 200 or 2000 mg/kg Ara-C or 50, 300 or 1800 mg/kg HU. At various intervals following drug, [3H]thymidine was administered i.p. and mice were killed 1 hr later. Tumor cells were analyzed for labeling index (LI) and grain count (GC) to determine the percentage of cells in S phase and the distribution of DNA synthesis rates among the labeled cells, respectively. Following each dose of HU, DNA synthesis was inhibited completely. Recovery of LI was rapid and approached control values by 6 hr. Following each dose of Ara-C, DNA synthesis was inhibited completely for at least 6 hr. Recovery of LI was first noted 6 hr following 20 mg/kg Ara-C and 9 hr following 200 mg/kg. Following both doses the LI reached 100% of the control value by 26 hr. GC analysis indicated that following Ara-C treatment, DNA synthesis was reinitiated first with cells with low GC from 6 to 12 hr followed by cells with increasing GC from 12 to 20 hr. The labeling intensity reached control values by 20 hr and an 'overshoot' occurred by 26 hr. These data suggest that the recovery of DNA synthesis rate is a gradual process. Survival data for mice receiving two doses of Ara-C indicated that the optimal interval for retreatment following the lower dose of Ara-C occurred by 6 hr as compared to 12--16 hr for the higher dose. These times coincided in both instances with recovery of LI to 33--50% of control values. Early recovery of LI may be the best method currently available for estimating the optimal time for retreatment with an S phase specific drug.     

Chronopharmacokinetics and Chronotoxicity of Lithium in Mice Eating Normal and Low-Sodium Diets

The temporal aspects of the pharmacokinetics and toxicity of lithium were studied in mice eating normal and low-sodium diets. ICR male mice, housed under a lightrdark (LD; 12:12) cycle, were injected with variable doses of lithium chloride i.p. A circadian rhythm was found in lithium clearance after a single administration in mice eating the normal diet showed the maximum value in the early dark phase and the minimum in the early light phase. The repeated administration of lithium did not affect the rhythm of the pharmacokinetics of the drug under the LD cycle. Although the low-sodium diet significantly decreased the lithium clearance, it did not influence the rhythm of the clearance. Higher toxicity was demonstrated in mice injected with the drug at the time of day with lower lithium clearance in the single-dose study but not in the repeated-doses study, regardless of the diet conditions. The low-sodium diet increased the acute and chronic toxicity of lithium. The results indicate that there is a circadian rhythm of acute toxicity and clearance of lithium after a single dose or repeated administration of the drug in mice eating normal and low-sodium diets and that the low-sodium diet increases lithium toxicity by reducing the clearance of the drug without influencing the rhythm characteristics.     

Chronopharmacokinetics and Chronotoxicity of Lithium in Mice Eating Normal and Low-Sodium Diets

The temporal aspects of the pharmacokinetics and toxicity of lithium were studied in mice eating normal and low-sodium diets. ICR male mice, housed under a lightrdark (LD; 12:12) cycle, were injected with variable doses of lithium chloride i.p. A circadian rhythm was found in lithium clearance after a single administration in mice eating the normal diet showed the maximum value in the early dark phase and the minimum in the early light phase. The repeated administration of lithium did not affect the rhythm of the pharmacokinetics of the drug under the LD cycle. Although the low-sodium diet significantly decreased the lithium clearance, it did not influence the rhythm of the clearance. Higher toxicity was demonstrated in mice injected with the drug at the time of day with lower lithium clearance in the single-dose study but not in the repeated-doses study, regardless of the diet conditions. The low-sodium diet increased the acute and chronic toxicity of lithium. The results indicate that there is a circadian rhythm of acute toxicity and clearance of lithium after a single dose or repeated administration of the drug in mice eating normal and low-sodium diets and that the low-sodium diet increases lithium toxicity by reducing the clearance of the drug without influencing the rhythm characteristics.     

Phenotypic and Genetic Analysis of Clock, a New Circadian Rhythm Mutant in Drosophila Melanogaster

Clock is a semidominant X-linked mutation that results in shortening the period of Drosophila melanogaster's free-running locomotor activity rhythm from ca. 24.0 to ca. 22.5 hr. This mutation similarly shortened the phase response curve, determined by resetting activity rhythms with light pulses. Eclosion peaks for Clk cultures were separated by only 22.5 hr instead of the normal 24 hr. Clk was mapped close to, but separable from, another rhythm mutation--period01--by recombination. The estimated distance between these two mutations was short enough to suggest that Clk could be a per allele. If this is the case, the new mutant is unique in that it, unlike other per variants, is associated with essentially normal 1-min courtship song rhythms when Clk is expressed in males. Also, the new rhythm variant could not, in contrast to a short-period per mutation, have its effects on free-running activity rhythms uncovered by deletions. This result, and the lack of coverage of Clk's effects by duplications, suggest that it is not a simple hypomorphic or amorphic mutation.     

Cyclophosphamide teratogenesis: evidence for compensatory responses to induced cellular toxicity

Cyclophosphamide (CP) administered ip to pregnant mice on day 10 of gestation (day of plug = day 0) is teratogenic (exencephaly, cleft palate, and limb malformations) at 20 mg/kg and embryolethal at higher doses. In the present study, CP was administered at 1, 5, 10, or 20 mg/kg on day 10 of gestation. Embryos were removed at 8 and 28 hr postdosing, and two embryos from each litter were immediately stained with Nile blue sulfate (NBS) to identify areas of cell death. The remaining embryos were frozen and forelimb buds subsequently removed for flow cytometric (FCM) analysis of the cellular DNA synthetic cycle. Additional litters were examined near term (day 17) for morphological abnormalities; these data were correlated with embryonic toxicity as detected by NBS staining and FCM analysis. Only the highest dose produced malformations. In marked contrast, a dose-related increase in the percentage of limb bud cells in the S (DNA synthetic) phase of the cell cycle was detectable at all doses. Inhibition of DNA synthesis was detected at all doses 8 hr post exposure and persisted through 28 hr for doses greater than or equal to 10 mg/kg. NBS staining indicated increased cell death in the alar plate of the neural tube 28 hr after exposure to 10 mg/kg CP and generally increased cell death in areas of rapid cell proliferation throughout the embryo at 20 mg/kg. The absence of an overt teratogenic response at dose levels that produced significant perturbation of the cell cycle indicates that a measure of embryonic damage can be compensated for or repaired. The implications of these findings for the existence of thresholds in developmental toxicity are discussed.     

The influence of60Co γ-irradiation of pea seeds on the thiamine biosýnthesis in 10-daý plants

Pea seeds were subjected to 1; 5 and 20 krad doses of⁶⁰Co γ-raýs. The irradiated seeds were planted in damp sand and in Petri vessels. After 10-daý vegetation at room temperature and under natural light conditions the content of the following components was determined in ýoung plants: free thiamine and thiamine pýrophosphate and drý substance. It was found that 1 krad dose stimulates the growth of the plant and increases the crop of its green parts. The doses within the range of 1–5 krads do not affect the production of thiamine. The content of the latter, particularlý in its free form, increases markedlý for the dose of 20 krads. However, such doses hamper the vegetation. In conclusion it seems that doses of the order of 1 krad lead to positive results in respect to the growth of the plants, however, neither thiamine biosýnthesis nor its phosphorýlation is stimulated under these conditions.     

Radiation inactivation ofSalmonella panama andEscherichia coli K 12 present on deep-frozen broiler carcasses

Summary Low doses of ionizing radiation have been used to extend the shelf life of refrigerated poultry carcasses and to reduce the numbers of Salmonellae present. This report gives results of experiments on irradiation of deep-frozen poultry carcasses which were, before freezing, artificially contaminated withSalmonella panama and with a nalidixic acid-resistantEscherichia coli K 12. The D-values (decimal reduction) obtained with the inoculated carcasses were compared with D-values obtained with carcasses which were slaughtered in the normal way.The D-values forS.panama and forE.coli K 12 were 64.9 krad and 55.9 krad in the dripwater. Under commercial conditions approximately 100 krad were required for one decimal reduction of the Enterobacteriaceae present.The D-values estimated on the skin were higher forS.panama than forE. coli K 12 (128.6 krad vs 57.6 krad). If it is assumed that 1 positive carcass in 10,000 is allowed, the deep-frozen carcasses should be irradiated with doses of at least 700 krad to be sure of the absence of the testedS. panama strain.     

Dose-Dependent Cytokinetic Changes Following 1-β-D-Arabinofuranosylcytosine and Hydroxyurea In L1210 and S-180 In Vivo

DNA synthesis inhibition and recovery in L1210 and S-180 ascites tumors following 1-β-D-arabinofuranosylcytosine (Ara-C) and hydroxyurea (HU) were measured autoradiographically as a basis for optimizing drug schedules. Tumor bearing mice, 10⁶ cells day O, were treated on day 4 with 20, 200 or 2000 mg/kg Ara-C or 50, 300 or 1800 mg/kg HU. At various intervals following drug, [³H]thymidine was administered i.p. and mice were killed 1 hr later. Tumor cells were analyzed for labeling index (LI) and grain count (GC) to determine the percentage of cells in S phase and the distribution of DNA synthesis rates among the labeled cells, respectively. Following each dose of HU, DNA synthesis was inhibited completely. Recovery of LI was rapid and approached control values by 6 hr. Following each dose of Ara-C, DNA synthesis was inhibited completely for at least 6 hr. Recovery of LI was first noted 6 hr following 20 mg/kg Ara-C and 9 hr following 200 mg/kg. Following both doses the LI reached 100% of the control value by 26 hr. GC analysis indicated that following Ara-C treatment, DNA synthesis was reinitiated first with cells with low GC from 6 to 12 hr followed by cells with increasing GC from 12 to 20 hr. the labeling intensity reached control values by 20 hr and an ‘overshoot’ occurred by 26 hr. These data suggest that the recovery of DNA synthesis rate is a gradual process. Survival data for mice receiving two doses of Ara-C indicated that the optimal interval for retreatment following the lower dose of Ara-C occurred by 6 hr as compared to 12–16 hr for the higher dose. These times coincided in both instances with recovery of LI to 33–50% of control values. Early recovery of LI may be the best method currently available for estimating the optimal time for retreatment with an S phase specific drug.