Cytogenetic analysis of mouse metaphase II oocytes following exposure to tritiated water

Female mice were given different dosages (0, 3.0, 7.5, 15.0, or 30 muCi/ml) of tritium in their drinking water continuously from 3 to 7 weeks of age to assess the effects on germ cell chromosomes. At 8-9 weeks of age, mice were superovulated and metaphase II oocytes were processed and C-banded for cytogenetic analyses. Chromatid acentric fragments were the only type of structural aberration detected, and their incidence was higher in controls than in any of the tritiated water (HTO) groups. Analysis of numerical chromosomal aberrations revealed that the incidence of hypoploid (N = 19) oocytes was higher in oocytes from mice who drank HTO as compared with controls. However, the effects of HTO upon aneuploidy induction was not definitive due to the increase the incidence of aberrations in mouse oocytes can be related to the low dose rate resulting from chronic HTO exposure and possibly death of tritium-damaged cells.     

Cell death (apoptosis) in mouse intestine after continuous irradiation with gamma rays and with beta rays from tritiated water

Apoptosis is a pattern of cell death involving nuclear pycnosis, cytoplasmic condensation, and karyorrhexis. Apoptosis induced by continuous irradiation with gamma rays (externally given by a 137Cs source) or with beta rays (from tritiated water injected ip) was quantified in the crypts of two portions of mouse bowel, the small intestine and descending colon. The time-course change in the incidence of apoptosis after each type of radiation could be explained on the basis of the innate circadian rhythm of the cells susceptible to apoptotic death and of the excretion of tritiated water (HTO) from the body. For 6-h continuous gamma irradiation at various dose rates (0.6-480 mGy/h) and for 6 h after injection of HTO of various radioactivities (0.15-150 GBq per kg body wt), the relationships between dose and incidence of apoptosis were obtained. Survival curves were then constructed from the curves for dose vs incidence of apoptosis. For the calculation of the absorbed dose from HTO, the water content both of the mouse body and of the cells was assumed to be 70%. One megabecquerel of HTO per mouse (i.e., 40 MBq/kg body wt) gave a dose rate of 0.131 mGy/h. The mean lethal doses (D0) were calculated for gamma rays and HTO, and relative biological effectiveness values of HTO relative to gamma rays were obtained. The D0 values for continuous irradiation with gamma rays were 210 mGy for small intestine and 380 mGy for descending colon, and the respective values for HTO were 130 and 280 mGy, indicating the high radiosensitivity of target cells for apoptotic death. The relative biological effectiveness of HTO relative to 137Cs gamma rays for cell killing in both the small intestine and the descending colon in the mouse was 1.4-2.1.     

Tritium distribution in newborn mice after providing mother mice with drinking water containing tritiated thymidine

Throughout gestation pregnant mice received drinking water which contained [methyl-3H]thymidine (18.5 kBq/ml). The newborn mice were divided into two groups. One group was nursed by their own mothers, which were further supplied with tritiated thymidine until 4 weeks after delivery (Experiment I). The other group was nursed by "nonradioactive mothers" which were given no tritiated thymidine (Experiment II). Tritium incorporation into the small molecular components of the acid-soluble fraction, lipid, RNA, DNA, and protein was analyzed for the newborn mice at various ages. In Experiment II, total radioactivity per gram tissue decreased initially after birth with a half life of 2.5-2.9 days in spleen, liver, intestine, stomach, thymus, lung, kidney, heart, and brain. At about 2 weeks after birth, a slower component of tritium elimination due mainly to the DNA-bound tritium appeared. Specific activity of DNA at birth was organ specific, highest in heart and lowest in thymus. Cumulative absorbed dose in various organs was estimated for the first 4 weeks after birth based upon an assumption that total and DNA-bound tritium are uniformly distributed. The result showed that organ specificity of dose accumulation is obvious for DNA-bound tritium, highest in spleen (1.15 mGy) and lowest in brain (0.13 mGy). It was also shown that the tritium supply from mother's milk is of minor importance for dose accumulation of DNA-bound tritium in the cell nuclei of organs of suckling mice.     

Gamete rescue in the African black rhinoceros (Diceros bicornis)

Mortality rates are high among captive African black rhinoceroses (Diceros bicornis), due to increased susceptibility to disease. The ability to rescue genetic material from individuals that die unexpectedly represents a practical approach to assist ex situ conservation efforts. The objectives of the present study were to attempt postmortem oocyte recovery from ovaries of African black rhinoceroses (N = 6) and to test the efficacy of equine protocols for rhinoceros oocyte IVM and IVF using cryopreserved rhinoceros sperm. The interval from ovary removal to oocyte recovery was 25.3 ± 13.9 h (mean ± SD). Ovaries were transported at 4 °C or 22 °C and effects of temperature on postmortem oocyte competence was evaluated. Numbers of oocytes collected per female averaged 15.8 ± 6.9. In total, 95 oocytes were recovered. Of these, 85 were inseminated using homologous sperm and 10 were inseminated using heterologous sperm. Overall, substantial numbers of viable oocytes were retrieved from African black rhinoceros ovaries 1 to 2 days postmortem from ovaries stored at ambient temperature. A proportion of these oocytes matured and underwent penetration and fertilization by heterologous or homologous frozen-thawed rhinoceros sperm. The reproductive competence of postmortem oocytes was further demonstrated by development of a single two-cell embryo. Despite the need for further refinements, gamete rescue in the rhinoceros has promise for producing rhinoceros embryos, as well as testing sperm functions in vitro.     

Cause of death and neoplasia in mice continuously exposed to very low dose rates of gamma rays

Four thousand 8-week-old SPF B6C3F1 mice (2000 of each sex) were divided into four groups, one nonirradiated (control) and three irradiated. The irradiated groups were exposed to (137)Cs gamma rays at dose rates of 21, 1.1 and 0.05 mGy day(-1) for approximately 400 days with total doses equivalent to 8000, 400 and 20 mGy, respectively. All mice were kept until natural death, and pathological examination was performed to determine the cause of death. Neoplasms accounted for >86.7% of all deaths. Compared to the nonirradiated controls, the frequency of myeloid leukemia in males, soft tissue neoplasms and malignant granulosa cell tumors in females, and hemangiosarcoma in both sexes exposed to 21 mGy day(-1) were significantly increased. The number of multiple primary neoplasms per mouse was significantly increased in mice irradiated at 21 mGy day(-1). Significant increases in body weights were observed from 32 to 60 weeks of age in males and females exposed to 1.1 mGy day(-1) and 21 mGy day(-1), respectively. Our results suggest that life shortening (Tanaka et al., Radiat. Res. 160, 376-379, 2003) in mice continuously exposed to low-dose-rate gamma rays is due to early death from a variety of neoplasms and not from increased incidence of specific neoplasms.     

Free oxygen radicals are generated at the time of aspiration of oocytes from ovaries that have been stored for a long time

In ischaemic tissues, reperfusion induces acute injury and functional changes. In this work, ovaries were stored for various times, and superoxide dismutase (SOD) and dimethylthiourea (DTMU) were used at the time of oocyte aspiration. We then attempted to determine whether free oxygen radicals are generated at oocyte aspiration and whether they impair the developmental competence of oocytes. Over 2 mM of DMTU and 1000 U/ml of SOD significantly improved the rate of blastulation 8 days after insemination. For ovaries that were preserved for 3 and 7 h, using antioxidants also significantly improved the rate of blastulation 8 days after insemination. However, no effect was observed on oocytes from ovaries preserved for 1 h. We examined how the antioxidants affected the presence of germinal vesicles, chromatin configuration, and polar body extrusion 6 or 21 h after culture. Chromatin configuration was classified into three groups according to the amount of chromatin condensation (group 1, strong condensation; group 2, moderate; group 3, slight). Storing ovaries for a long time decreased the frequency of occurrence of group 2, but increased groups 1 and 3. However, using antioxidants at oocyte aspiration decreased the frequency of group 3 and increased group 1. Moreover, there was no difference in the rate of germinal vesicle breakdown and polar body extrusion. Our results show that preserving ovaries for a long time induces the generation of free oxygen radicals and that these chemicals impair oocyte viability. Using antioxidants at oocyte aspiration was beneficial for embryo production.     

No lengthening of life span in mice continuously exposed to gamma rays at very low dose rates

Late effects of continuous exposure to ionizing radiation are potential hazards to workers in radiation facilities as well as to the general public. Recently, low-dose-rate and low-dose effects have become a serious concern. Using a total of 4000 mice, we studied the late biological effects of chronic exposure to low-dose-rate radiation as assayed by life span. Two thousand male and 2000 female 8-week-old specific-pathogen-free (SPF) B6C3F1 mice were randomly divided into four groups (one nonirradiated control and three irradiated). Irradiation was carried out for approximately 400 days using (137)Cs gamma rays at dose rates of 21 mGy day(-1), 1.1 mGy day(-1) and 0.05 mGy day(-1) with total doses equivalent to 8000 mGy, 400 mGy and 20 mGy, respectively. All mice were kept under SPF conditions until they died spontaneously. Statistical analyses showed that the life spans of mice of both sexes irradiated with 21 mGy day(-1) (P < 0.0001) and of females irradiated with 1.1 mGy day(-1) (P < 0.05) were significantly shorter than those of the control group. Our results show no evidence of lengthened life span in mice continuously exposed to very low dose rates of gamma rays.     

Nutritional restriction of pre-pubertal liveweight gain impairs ovarian follicle growth and oocyte developmental competence of replacement gilts

The objective was to investigate the effects of moderate restriction of pre- and peri-pubertal liveweight gain on ovarian development and oocyte meiotic competence. At 70 d of age, and 27.7 ± 0.4 kg liveweight (LW), 64 Large White/Landrace crossbred gilts were allocated to two treatment groups (n = 32 gilts/treatment); one group was fed to attain a LW of 70 kg at 161 d of age (LIGHT), while the other group was fed to reach 100 kg LW (HEAVY). At 161 d of age, half of the gilts in each group (n = 16) were fed to gain LW at 0.5 kg/d (LOW), while the remaining half (n = 16) were fed to gain LW at 1.0 kg/d (HIGH) between 161 and 175 d of age, at which point they were killed and ovaries collected. For each gilt, surface antral follicles were counted and aspirated according to three size categories: 1-2.9 mm (small); 3-6 mm (medium); and > 6 mm (large). Follicles were pooled for each size class and treatment. Cumulus-oocyte-complexes (COC) recovered from small and medium follicles were matured in vitro (IVM) for 44 to 46 h, and meiotic maturation assessed. There was an effect of treatment (LIGHT versus HEAVY) on the number of medium sized follicles: 25.1 ± 2.59 versus 34.3 ± 2.60 (P < 0.05). The ovaries of LOW gilts had more small follicles and fewer medium follicles compared to those of HIGH gilts: 92.8 ± 8.35 versus 59.8 ± 5.24, and 25.1 ± 2.59 versus 32.5 ± 2.86 (P < 0.05). Target LW at 161 d did not affect meiotic progression of oocytes. However, LOW compared to HIGH LW gain between 161 and 175 d resulted in fewer oocytes reaching MII (0.40 versus 0.54; P < 0.05). In conclusion, moderately restricting feed intake impaired follicle growth beyond 3 mm and reduced oocyte meiotic competence. Further, although a carry-over effect of long-term feed restriction on follicle growth was evident, acute changes in feed intake during the 14 d prior to ovary collection had the greatest effect on oocyte nuclear maturation in vitro.     

Histopathological changes in the ovary following acute and chronic low-level tritium exposure to mice in vivo

Swiss albino mice were exposed to various doses of tritiated water, either through intraperitoneal injection (acute) or orally (chronic) for various lengths of time. The ovaries were examined for qualitative histopathological and quantitative changes in the number of oocytes. All experimental groups displayed varying degrees of dose dependent radiolesions. It was found that chronic irradiation was more damaging than multiple weekly injection, which in turn was more damaging than a single injection. Also, radiosensitivity varied with the age of the mice.     

Impact of low doses of tritium on the marine mussel, Mytilus edulis: genotoxic effects and tissue-specific bioconcentration

Despite growing scientific, public and regulatory concern over the discharge of radioactive substances, no serious attempts have been made to develop a rationale to evaluate the impact of environmentally relevant radionuclides in the aquatic environment. In this study, we have evaluated the genotoxic effects and tissue-specific concentration of tritium (added as tritiated water, HTO) in the adult life stage of the edible mussel, Mytilus edulis. The genotoxic effects were quantified in terms of the induction of: (a) micronuclei (MN), and (b) DNA single-strand breaks/alkali-labile sites using alkaline single-cell gel electrophoresis (Comet assay) in the haemocytes of exposed animals. The assays were optimised and validated using a range of concentrations (18-56 mgl(-1)) of ethylmethane sulfonate (EMS), a direct-acting reference genotoxic agent, over different exposure periods. Mussels were exposed to a series of concentrations of HTO equivalent to a dose range from 12 to 485 muGyh(-1) for 96 h, and different tissues and organs were then extracted and analysed. The study revealed a dose-dependent increase in the response for both the MN test and the Comet assay and for both EMS and HTO. In addition, HTO delivering dose rates below 500 muGyh(-1) was shown to be capable of inducing genetic damage in the haemocytes of these bivalves. The study also showed that inorganic tritium accumulated differentially in mussel tissues in a dose-dependent manner, with the gut accumulating the highest amount of radioactivity, followed by the gill, mantle, muscle, foot and byssus thread. The faeces and pseudo-faeces accumulated least radioactivity over the exposure period. Differential accumulation of radionuclides has significant implications for biomonitoring programmes, for this and other aquatic organisms. The study also suggests that the generic dose limits recommended by the International Atomic Energy Agency for the protection of aquatic biota might not be applicable to all aquatic organisms.     

Sister chromatid exchanges in bone marrow cells of mice maintained on tritiated water

The ability of tritium to induce sister chromatid exchanges (SCEs) has been investigated in male mice of the Hale-Stoner-Brookhaven strain maintained on drinking water containing 3.0 microCi/ml tritiated water (HTO). At selected intervals after 28-261 days of consuming HTO, the frequency of SCEs and the kinetics of cellular proliferation were measured in bone marrow cells of animals maintained on HTO, and in age-matched control groups, by 5-bromo-2'-deoxyuridine labelling methods. A statistically significant (1 percent level) elevation of SCEs was observed after 81, 163, 192, 247 and 261 days of HTO ingestion. The frequency of induced SCEs increased linearly with the ingestion time. These results are of particular interest since ionizing radiation is generally not considered to be an efficient inducer of SCEs.     

Studies on oocyte maturation of the medaka, Oryzias latipes. V. On the structure of steroids that induce maturation in vitro

The response of oocytes within isolated follicles (800-950 micron in diameter) to various steroids was examined with the teleost fish, Oryzias latipes. Continuous exposure of oocytes, which were removed from ovarian investments 17 hours before predicted germinal vesicle breakdown (GVBD), to C19- or C21-steroids brought about maturation in vitro but never triggered ovulation. The steroids effective in inducing maturation have in common a C=0 (or alpha-OH) group at 3C and a beta-OH group at 17C in the C19-steroids, and a C=O (or beta-OH) group at 3C and a C=O (or alpha-OH) group at 20C in the C21-steroids, in addition to an delta4- or delta5-unsaturated for 5alpha-saturated configuration. The orientation of the hydrogen at 5C seems to be critical in determining the ability of a particular steroid to stimulate oocyte maturation. Maturation of oocytes in the ovaries of hypophysectomized females was induced by administering progesterone, but the mature oocytes did not subsequently undergo ovulation. Thus the steroid hormone is capable of inducing oocyte maturation but apparently does not participate directly in the ovulation of Oryzias latipes oocytes.     

Formation of lipid reserves in fat body and eggs of the yellow fever mosquito, Aedes aegypti

We examined the accumulation of lipids in adult females of the mosquito, Aedes aegypti. Females emerged with about 100 μg lipid in the fat body. With access to sugar water lipids increased over seven days to 300 μg. After a blood meal on day five, sugar-fed females accumulated 120-140 μg of lipids in their ovaries within 2 days. At the same time the lipid content of the fat body decreased by 100 μg, indicating transfer of lipids from fat body to oocytes. Experiments in which fat body lipids were prelabelled support this conclusion. Label was transferred to oocytes: in mature oocytes the specific radioactivity of lipids was 80% of the specific radioactivity of prelabeled fat body lipids. Components of blood meals are also used to synthesize oocyte lipids. Fat bodies of females starved for four days had only 27 μg of lipids left. When these females were given a blood meal, they matured oocytes, although the number of ooyctes was reduced and ovaries contained only half the amount of lipids found in ovaries of females which had first fed on sugar water. Fat body lipids of these females had only slightly increased to 36 μg. This demonstrates that female Ae. aegypti use sugar to synthesize lipids, but they can also use components of blood for this purpose.     

Pinealectomy and ovarian development in the grey mullet, Liza ramada

Adult female specimens of Liza ramada were pinealectomized and sham-pinealectomized, and the development of their ovaries was followed over a period of 14 weeks and compared with those of untreated controls. Pinealectomized specimens exposed to long photoperiod (16L/8D) for 14 weeks, showed undeveloped ovaries, with a maximum oocyte diameter of less than 100 μm, and a gonadosomatic index of 0·6 similar to that of sham-pinealectomized and control specimens. In pinealectomized females exposed to short photoperiod (8L/16D) for 6 weeks, the mean diameter of oocytes was 270 μm v . 155 μm in control and sham-pinealectomized specimens. After 9 weeks, the oocytes in pinealectomized specimens reached 430 μm as against 265 μm in the controls. Within 14 weeks of pinealectomy, mean oocyte diameter was 480 um while it was 400 μm in controls and sham-pinealectomized specimens. It is tentatively concluded that the pineal complex has an inhibitory effect on ovarian function in Liza ramada exposed to short photoperiod.     

Relationship between growth and meiotic maturation of the mouse oocyte

Oocytes of various sizes were isolated from trypsinized ovaries of juvenile mice, cultured in a chemically defined medium, and scored for the resumption and completion of meiotic maturation. Oocytes recovered from mice younger than 15 days remained in the germinal vesicle stage, whereas those from mice 15 days or older resumed meiosis at a frequency which increased with the age of the mice. The mean diameter of the oocytes recovered also increased with the age of the mice. Within individual litters, the mean diameter of oocytes which failed to mature (incompetent oocytes) was significantly less than that of oocytes which matured (competent oocytes). The frequency of premature metaphase I arrest decreased markedly as the age of the mice and oocyte volume increased. These results suggest that the ability to resume meiosis is acquired at a specific stage of oocyte growth in the juvenile mouse, and that the ability to complete meiotic maturation is acquired subsequently. These oocytes provide an in vitro system with which to study the control of meiosis in the mammal.     

Increasing age influences uterine integrity, but not ovarian function or oocyte quality, in the cheetah (Acinonyx jubatus)

Although the cheetah (Acinonyx jubatus) routinely lives for more than 12 yr in ex situ collections, females older than 8 yr reproduce infrequently. We tested the hypothesis that reproduction is compromised in older female cheetahs due to a combination of disrupted gonadal, oocyte, and uterine function/integrity. Specifically, we assessed 1) ovarian response to gonadotropins; 2) oocyte meiotic, fertilization, and developmental competence; and 3) uterine morphology in three age classes of cheetahs (young, 2-5 yr, n = 17; prime, 6-8 yr, n = 8; older, 9-15 yr, n = 9). Ovarian activity was stimulated with a combination of equine chorionic gonadotropin and human chorionic gonadotropin (hCG), and fecal samples were collected for 45 days before gonadotropin treatment and for 30 days after oocyte recovery by laparoscopy. Twenty-six to thirty hours post-hCG, uterine morphology was examined by ultrasound, ovarian follicular size determined by laparoscopy, and aspirated oocytes assessed for nuclear status or inseminated in vitro. Although no influence of age on fecal hormone concentrations or gross uterine morphology was found (P > 0.05), older females produced fewer (P < 0.05) total antral follicles and oocytes compared to younger counterparts. Regardless of donor age, oocytes had equivalent (P > 0.05) nuclear status and ability to reach metaphase II and fertilize in vitro. A histological assessment of voucher specimens revealed an age-related influence on uterine tissue integrity, with more than 87% and more than 56% of older females experiencing endometrial hyperplasia and severe pathologies, respectively. Our collective findings reveal that lower reproductive success in older cheetahs appears to be minimally influenced by ovarian and gamete aging and subsequent dysfunction. Rather, ovaries from older females are responsive to gonadotropins, produce normative estradiol/progestogen concentrations, and develop follicles containing oocytes with the capacity to mature and be fertilized. A more likely cause of reduced fertility may be the high prevalence of uterine endometrial hyperplasia and related pathologies. The discovery that a significant proportion of oocytes from older females have developmental capacity in vitro suggests that in vitro fertilization and embryo transfer may be useful for "rescuing" the genome of older, nonreproductive cheetahs.     

Effects of eCG and FSH on ovarian response, recovery rate and number and quality of oocytes obtained by ovum pick-up in Holstein cows

The goal of the present study was to compare the ovarian response, oocyte yields per animal, and the morphological quality of oocytes collected by ultrasound guided follicular aspiration from Holstein cows treated either with FSH or eCG. Twenty four normal cyclic, German Holstein cows were randomly divided into two groups. Fourteen cows received 3000 IU eCG on day-4 prior to ovum pick-up (OPU) (day 0), 2 days later (day-2), 625 microg cloprostenol was administered. On day-1 GnRH was administered i.m. and 24h later OPU (day 0) was performed. In ten cows a total dose of 500 IU follicle stimulating hormone (Pluset) was administered intramuscularly in a constant dosage for 4 days with intervals of 12h, starting on day-5. Luteolysis was induced by application of 625 microg cloprostenol on day-2. On day-1 (24h after the last FSH treatment) GnRH was administered i.m. and 24h later OPU (day 0) was performed. Ovarian follicles were visualized on the ultrasound monitor, counted and recorded. All visible antral follicles were punctured. Recovered oocytes were graded morphologically based on the cumulus investment. Average follicle number in ovaries was higher in FSH group than eCG group (p<0.05). Oocyte yields per animal did not differ between FSH and eCG groups. The proportion of grade A oocytes was higher in the FSH group in the than eCG group (p<0.05). Likewise, rate of grade C oocytes in FSH group were lower than eCG group (p<0.05). In conclusion, these results suggest that ovarian response, follicle number in ovaries and oocyte quality are affected by the type of gonadotropin and FSH is better alternative than eCG for OPU treatment.     

Development of mouse and rat oocytes in chimeric reaggregated ovaries after interspecific exchange of somatic and germ cell components

The germ cell and somatic cell compartments of newborn rat and mouse ovaries, which contain only primordial stage follicles, were completely exchanged and reaggregated to produce xenogeneic chimeric ovaries. The reaggregated ovaries were grafted beneath the renal capsules of ovariectomized SCID mice to develop for periods up to 21 days. Xenogeneic follicles developed with essentially normal morphological characteristics. Both rat and mouse oocytes with species-specific characteristics grew within follicles that were composed of somatic cells exclusively of the alternative species. Rat oocytes grown in mouse follicles became competent to resume meiosis, and progressed to metaphase II when they were removed from follicles and cultured. In addition, mouse oocytes grown in rat follicles underwent fertilization and preimplantation development in vitro, and developed to term after embryos were transferred to pseudopregnant mouse foster mothers. Therefore, despite an estimated 11 million years of divergent evolution, oocytes and somatic cells of rat and mouse ovaries can be exchanged and can produce functional oocytes. It is concluded that factors involved in oocyte-somatic cell interactions necessary to support oocyte development and appropriate differentiation of the oocyte-associated granulosa cells are conserved between rats and mice. Moreover, although granulosa cells play important roles in oocyte development, the development of species-specific characteristics of oocytes occurs without apparent modification by a xenogeneic follicular environment.     

Oocyte maturation in white sturgeon,Acipenser transmontanus: some mechanisms and applications

Synopsis The ovaries of four pre-spawning white sturgeon females were sampled and their oocytes incubated in the presence of eight gonadotropin preparations, 21 steroids, a prostaglandin and a catacholamine. Among the gonadotropin preparations, acetone dried pituitary gland powder from white sturgeon, common carp and chum salmon (in decreasing order of potency) were capable of inducing oocyte maturation (germinal vesicle breakdown — GVBD), while human chorionic gonadotropin, pregnant mare's serum gonadotropin, equine luteinizing hormone, bullfrog gonadotropin, and a stellate sturgeon pituitary chromatographic fraction capable of inducing testosterone production in white sturgeon testicular tissue failed to elicit any oocyte maturation response. The progesterone derivatives were the most potent steroid inducers of GVBD, followed closely by several corticosteroids. In vitro incubation of white sturgeon oocytes, in the presence of a suitable steroid (progesterone), can be used as a diagnostic tool in screening out unresponsive females for induced spawning work. The two remaining compounds, prostaglandin F_2a and epinephrine, failed to cause ovulation in progesterone-matured white sturgeon oocytes.     

Dose-response relationship for the induction of structural chromosome aberrations in human spermatozoa after in vitro exposure to tritium beta-rays

The effects of tritium (HTO) beta-rays on human sperm chromosomes were studied using our interspecific in vitro fertilization system between human spermatozoa and zona-free hamster oocytes. Semen samples were treated with media containing 1.53-24.3 mCi/ml HTO for about 80 min. 1290 spermatozoa from the controls and 1842 spermatozoa from the irradiated groups were karyotyped. The incidence of spermatozoa with structural chromosome aberrations increased linearly with increasing dosage. Breakage-type aberrations occurred far more frequently than exchange-type. Chromosome-type aberrations appeared far more frequently than chromatid-type. All of these types of aberrations showed linear dose-dependent increases. The RBE values of HTO beta-rays relative to X-rays were calculated for the above-mentioned 5 indices, respectively. Their RBE values ranged from 1.89 to 3.00 when the absorbed dose was estimated to be the minimum, whereas the values ranged between 1.04 and 1.65 when the absorbed dose was estimated to be the maximum.