Electromagnetic Field (EMF) Radiation Alters Estrogen Release from the Pig Myometrium during the Peri-Implantation Period

An electromagnetic field (EMF) may affect the functions of uterine tissues. This study hypothesized that EMF changes the estrogenic activity of pig myometrium during the peri-implantation period. Tissue was collected on days 15-16 of the gestation and incubated in the presence of EMF (50 and 120 Hz, 2 and 4 h). The cytochrome P450 aromatase type 3 (CYP19A3) and hydroxysteroid 17β dehydrogenase type 4 (HSD17B4) mRNA transcript abundance, cytochrome P450arom (aromatase), and 17β hydroxysteroid dehydrogenase 17βHSD) protein abundance and estrone (E₁) and estradiol-17β (E₂) release were examined using Real-Time PCR, Western blot and radioimmunoassay. Selected myometrial slices were treated with progesterone (P₄) to determine whether it functions as a protector against EMF. CYP19A3 mRNA transcript abundance in slices treated with EMF was less at 50 Hz (2 h) and greater at 120 Hz (2 and 4 h). HSD17B4 mRNA transcript was greater in slices treated with EMF at 120 Hz (2 h). Progesterone diminished EMF-related effects on CYP19A3 and HSD17B4. When P₄ was added, EMF had suppressive (50 and 120 Hz, 2 h) or enhancing (50 Hz, 4 h) effects on aromatase abundance. The E₁ release was lower after 4 h of EMF treatment at 50 Hz and P₄ did not protect myometrial E₁ release. In conclusion, EMF alters the synthesis and release of E₁ and did not affect E₂ release in the myometrium during the peri-implantation period.

Laser irradiation pretreatment improves endometrial preparation of frozen-thawed embryo transfer in recurrent implantation failure patients

Recurrent implantation failure (RIF) remains a clinical dilemma. Helium-Neon (He-Ne) laser irradiation has recently become more popular under certain clinical conditions. Given the unique therapeutic effects, we were interested in determining whether pretreatment with He-Ne laser irradiation prior to frozen-thawed embryo transfer (FET) would improve the microcirculation and cause the release of growth factors and cytokines, thus improving endometrial receptivity and the clinical pregnancy rates. Patients chose for themselves whether to proceed with (n = 29) or without (n = 31) pretreatment with He-Ne laser irradiation prior to FET. The clinical pregnancy rate (37.9%) and implantation rate (20.3%) were higher in the laser-treatment group than in the control group (35.5% and 15.9%, respectively, p = .844 and .518, respectively). The live birth rate was higher in the laser-treatment group (27.6% vs. 25.8%, respectively, p = .876) and the miscarriage rate was lower in the laser-treatment group (18.2% and 27.3%, respectively, p = .611). No side effects or complications from laser irradiation were encountered in patients who received the laser treatment. We concluded that pretreatment with He-Ne laser prior to FET may be an alternative choice for RIF-affected women; however, additional well-designed prospective studies are necessary to determine the precise clinical value of this treatment.

Effects of melatonin administration on embryo implantation and offspring growth in mice under different schedules of photoperiodic exposure

BACKGROUND

Embryo implantation is crucial for animal reproduction. Unsuccessful embryo implantation leads to pregnancy failure, especially in human-assisted conception. Environmental factors have a profound impact on embryo implantation. Because people are being exposed to more light at night, the influence of long-term light exposure on embryo implantation should be explored.

METHODS

The effects of long photoperiodic exposure and melatonin on embryo implantation and offspring growth were examined. Long photoperiodic exposure (18:6 h light:dark) was selected to resemble light pollution. Melatonin (10^-2, 10^-3, 10^-4, 10^-5 M) was added to the drinking water of mice starting at Day 1 (vaginal plugs) until delivery.

RESULTS

Melatonin treatment (10^-4,10^-5 M) significantly increased litter sizes compared to untreated controls (12.9 ± 0.40 and 12.2 ± 1.01 vs. 11.5 ± 0.43; P < 0.05). The most effective concentration of melatonin (10^-4 M) was selected for further investigation. No remarkable differences were found between melatonin-treated mice and controls in terms of the pups' birth weights, weaning survival rates, and weaning weights. Long photoperiodic exposure significantly reduced the number of implantation sites in treated mice compared to controls (light/dark, 12/12 h), and melatonin rescued this negative effect. Mechanistic studies revealed that melatonin enhanced the serum 17β-estradiol (E₂) levels in the pregnant mice and upregulated the expression of the receptors MT1 and MT2 and p53 in uterine tissue. All of these factors may contribute to the beneficial effects of melatonin on embryo implantation in mice.

CONCLUSION

Melatonin treatment was associated with beneficial effects in pregnant mice, especially those subjected to long photoperiodic exposure. This was achieved by enhanced embryo implantation. At the molecular level, melatonin administration probably increases the E₂ level during pregnancy and upregulates p53 expression by activating MT1/2 in the uterus. All of the changes may improve the microenvironment of the uterus and, thus, the outcomes of pregnancy.

2.45 GHz microwave irradiation-induced oxidative stress affects implantation or pregnancy in mice, Mus musculus

The present experiment was designed to study the 2.45 GHz low-level microwave (MW) irradiation-induced stress response and its effect on implantation or pregnancy in female mice. Twelve-week-old mice were exposed to MW radiation (continuous wave for 2 h/day for 45 days, frequency 2.45 GHz, power density=0.033549 mW/cm(2), and specific absorption rate=0.023023 W/kg). At the end of a total of 45 days of exposure, mice were sacrificed, implantation sites were monitored, blood was processed to study stress parameters (hemoglobin, RBC and WBC count, and neutrophil/lymphocyte (N/L) ratio), the brain was processed for comet assay, and plasma was used for nitric oxide (NO), progesterone and estradiol estimation. Reactive oxygen species (ROS) and the activities of ROS-scavenging enzymes- superoxide dismutase, catalase, and glutathione peroxidase-were determined in the liver, kidney and ovary. We observed that implantation sites were affected significantly in MW-irradiated mice as compared to control. Further, in addition to a significant increase in ROS, hemoglobin (p<0.001), RBC and WBC counts (p<0.001), N/L ratio (p<0.01), DNA damage (p<0.001) in brain cells, and plasma estradiol concentration (p<0.05), a significant decrease was observed in NO level (p<0.05) and antioxidant enzyme activities of MW-exposed mice. Our findings led us to conclude that a low level of MW irradiation-induced oxidative stress not only suppresses implantation, but it may also lead to deformity of the embryo in case pregnancy continues. We also suggest that MW radiation-induced oxidative stress by increasing ROS production in the body may lead to DNA strand breakage in the brain cells and implantation failure/resorption or abnormal pregnancy in mice.

Selection against spermatozoa with fragmented DNA after postovulatory mating depends on the type of damage

BACKGROUND

Before ovulation, sperm-oviduct interaction mechanisms may act as checkpoint for the selection of fertilizing spermatozoa in mammals. Postovulatory mating does not allow the sperm to attach to the oviduct, and spermatozoa may only undergo some selection processes during the transport through the female reproductive tract and/or during the zona pellucida (ZP) binding/penetration.

METHODS

We have induced DNA damage in spermatozoa by two treatments, (a) a scrotal heat treatment (42 degrees C, 30 min) and (b) irradiation with 137Cs gamma-rays (4 Gy, 1.25 Gy/min). The effects of the treatments were analyzed 21-25 days post heat stress or gamma-radiation. Postovulatory females mated either with treated or control males were sacrificed at Day 14 of pregnancy, and numbers of fetuses and resorptions were recorded.

RESULTS

Both treatments decreased significantly implantation rates however, the proportion of fetuses/resorptions was only reduced in those females mated to males exposed to radiation, indicating a selection favoring fertilization of sperm with unfragmented DNA on the heat treatment group. To determine if DNA integrity is one of the keys of spermatozoa selection after postovulatory mating, we analyzed sperm DNA fragmentation by COMET assay in: a) sperm recovered from mouse epididymides; b) sperm recovered from three different regions of female uterine horns after mating; and c) sperm attached to the ZP after in vitro fertilization (IVF). Similar results were found for control and both treatments, COMET values decreased significantly during the transit from the uterine section close to the uterotubal junction to the oviduct, and in the spermatozoa attached to ZP. However, fertilization by IVF and intracytoplasmatic sperm injection (ICSI) showed that during sperm ZP-penetration, a stringent selection against fragmented-DNA sperm is carried out when the damage was induced by heat stress, but not when DNA fragmentation was induced by radiation.

CONCLUSION

Our results indicate that in postovulatory mating there is a preliminary general selection mechanism against spermatozoa with low motility and fragmented-DNA during the transport through the female reproductive tract and in the ZP binding, but the ability of the ZP to prevent fertilization by fragmented-DNA spermatozoa is achieved during sperm-ZP penetration, and depends on the source of damage.

Laser-assisted hatching increases pregnancy and implantation rates in cryopreserved embryos that were allowed to cleave in vitro after thawing: a prospective randomized study

BACKGROUND

Cryopreservation of embryos may lead to zona hardening that may compromise in vivo hatching and implantation following thawing and transfer. Assisted hatching (AH) has been advocated as a means of assisting the natural hatching process and enhancing implantation.

METHODS

The aim of this study was to assess in a prospective randomized manner the effect of laser-assisted hatching (LAH) on implantation as well as clinical and multiple pregnancy rates (the primary outcome) after the transfer of frozen-thawed embryos. All embryos were thawed the day before transfer, and LAH was performed the next day on embryos that cleaved. Control group consisted of embryos that were transferred without AH.

RESULTS

The performance of LAH significantly increased implantation (9.9 versus 20.1%, P < 0.01), clinical pregnancy (27.3 versus 40.9, P < 0.05) and multiple pregnancy rates (16 versus 40.3%, P < 0.07). In the LAH group, significantly more excess embryos that were left in culture hatched in vitro.

CONCLUSIONS

LAH improves the outcome of frozen-thawed embryo transfer when performed before transfer on embryos that were allowed to cleave.

Effects of low-frequency magnetic fields on implantation in rats

Effects of 50-Hz sinusoidal magnetic fields (MFs) on embryo implantation, serum 17beta-estradiol, progesterone, testosterone, and melatonin levels, and on estrogen receptor (ER) and progesterone receptor (PgR) densities in the uterus were studied during the preimplantation and implantation periods in rats. Pregnant Wistar rats were exposed to magnetic r.m.s. field strengths of 10 or 100 A/m (13 or 130 microT) or sham-exposed (controls) from day 0 of pregnancy for 24 h/day and killed during light and dark periods between 70 h and 176 h after ovulation. MFs did not influence the mean total number of implantations. The nocturnal mean serum melatonin concentration decreased by 34 and 38% at 10 and 100 A/m, respectively. At the same time, the first embryos, at an early developmental stage, arrived in the uterus in the MF-exposed groups. Serum estradiol and progesterone levels did not significantly change. Nuclear PgR and ER densities in the uterus decreased before implantation and there was an increased incidence of early stage embryos and fewer hatched embryos were found in the uterus at 100 A/m. During the early implantation period, the uterine cytosolic ER/PgR-ratio was increased at 100 A/m and no implants were concomitantly found in uterus. The nuclear ER/PgR-ratio decreased during implantation in both MF-groups due to decreased nuclear ER density. At the same time, 19% and 15% of the embryos (calculated from the corpora luteae) at 10 and 100 A/m, respectively, were yet morulae and not implanted. In summary, the results show that MFs do not impair implantation in rats although there may be some borderline changes in the transport and development of embryos and associated endocrinologic parameters.

Increased resorptions in CBA mice exposed to low-frequency magnetic fields: an attempt to replicate earlier observations

This paper has two aims. First, it reports the findings of a study on the effects of low-frequency magnetic fields on reproduction. Second, it serves as an example of an attempt to replicate the results of an experimental study in an independent laboratory and discusses some of the problems of replication studies. To try to replicate the findings of a study reporting increased resorptions (fetal loss) in mice exposed to 20 kHz magnetic fields with sawtooth waveform and to study the possible effects of 50 Hz sinusoidal fields, pregnant mice were exposed to magnetic fields from day 0 to 18 of pregnancy, 24 h per day. The flux densities of the vertical magnetic fields were 15 microT (peak-to-peak) at 20 kHz and 13 or 130 microT (root mean square) at 50 Hz. Two strains of animals were used: CBA/S mice imported from the laboratory reporting the original observations, and a closely related strain CBA/Ca. The CBA/S mice were cleaned of pathogenic microbes and parasites before they were imported into our laboratory. The magnetic field exposures did not affect resorption rate in CBA/Ca mice. In CBA/S, the frequency of resorptions was higher in the exposed mice than in the control group. However, the increase was not significantly different from either the no-effect hypothesis or the results of the original study we were attempting to replicate. Differences between the two studies and difficulties in interpreting the results are discussed. It is concluded that the results tend more to support than argue against increased resorptions in CBA/S mice exposed to the 20 kHz magnetic field. The results demonstrate that animal strain is an important variable in bioelectromagnetics research: even closely related strains may show different responses to magnetic field exposure.

Lethal and teratogenic effects in two successive generations of the HLG mouse strain after radiation exposure of zygotes -- association with genomic instability?

We analysed the transmission of lethal and teratogenic events to the subsequent generation in HLG/Zte mice after exposure of the zygote stage to 1 Gy X-rays. As observed in previous studies, our results on teratogenic events occurring in the same generation, which was exposed during the zygote stage, reveal a significantly higher risk for the induction of gastroschisis. Interesting new insights came from the study of lethal and teratogenic effects in the generation obtained after mating female mice, which were exposed during their zygote stage, to unexposed males. An approximately 2-fold higher level of damage was manifest in this generation compared with controls, expressed mainly as a significant increase of prenatal mortality (P<0.01). Although there was an increase in the number of malformed fetuses on day 19 of gestation (6.5% cases of gastroschisis compared to 3.5% in the controls), the frequency of gastroschisis in the exposed group was just not statistically significant (P>0.05). These results are in line with the hypothesis that genomic instability is involved in the damage seen after radiation exposure of the zygote stage of HLG mice.

Factors of importance for implantation and problems after treatment for childhood cancer

The uterus is of fundamental importance to reproduction; it nourishes the early embryo and accommodates growth and differentiation of the developing fetus. It is thus possible that the modalities employed to treat childhood cancer, that is; chemotherapeutic agents, and particularly irradiation, may result in damage to the uterine structure (musculature and local vasculature), with potential impairment of normal uterine function and thus increased risk of subsequent defective implantation. This may result in an impaired reproductive outcome (increased risk of spontaneous abortion, preterm labour, and low-birth-weight infants). Thus the reproductive problems foreseen following treatment of childhood cancer will be 1) ovarian failure or impaired ovarian activity and 2) uterine/endometrial structural and functional damage. The mode of treatment and age at its administration will be the major determinants of residual ovarian and uterine function. To understand the mechanisms that may be responsible for potential problems in reproductive function after treatment, it is essential to consider the mechanisms governing normal early pregnancy. Ovarian estradiol (E) and progesterone (P) secreted in a cyclical manner orchestrate the spatial and temporal morphological and functional changes in the endometrium required for implantation. In the absence of sex steroids, the endometrium is inactive. Implantation takes place in the midsecretory phase, that is, 5-9 days postovulation. E and P act sequentially to regulate cellular concentrations of their respective receptors and in turn gene transcription events are initiated to prepare the endometrium for implantation. A complex interaction exists between the network of uterine cells (epithelial, stroma, vascular, haemopoietic) and the endocrine system. Several key factors implicated in the implantation process will be addressed. There is published evidence that reports the risk of pubertal failure and early menopause after treatment for childhood cancer and, in those women who continue with ovarian activity and achieve pregnancy, a risk of poor reproductive outcome. It is likely that radiation damage to the uterus will adversely effect pregnancy potential. Our own group has reported impaired uterine characteristics in women after abdominal irradiation. More recently, we have shown that lower doses of radiotherapy (as with total-body irradiation) may be associated with a potential for improved uterine characteristics in response to physiological sex steroid replacement. The outlook after chemotherapy alone may be more optimistic; our early data support a normal uterine morphological response. Reproductive outcome in these patients remains unpredictable, so simple noninvasive assessment of uterine characteristics may provide data of predictive value with respect to future fertility potential.

Effects on female fertility and germinal cells in prepubertal and adult rats (Rattus norvegicus) after X-ray irradiation

In this work we analyse the effects of ionizing radiation in prepubertal and adult female rats, using as parameters, implantation sites, embryonic loss, and synaptonemal complex (SC) analysis of the female F1 of the pregnant rats. Our preliminary results show a decrease statistically significant in fertility of irradiated groups, but cytogenetic analysis did not shown any inherited damage attributed to radiation. At the same time, our results seem to indicate a higher resistance of oocytes from prepubertal rats and support the possible use of GnRH agonists as oestrus cycle suppressors to turn adult rats into gonadal quiescence.

Nutritional stress-induced implantation failure in laboratory mice: inhibition by continuous illumination

The implantation failure in newly inseminated mice induced by food deprivation for 48 hr, beginning at 0900 hrs on day 4 post coitum, was prevented by simultaneous exposure to light continuously for 48 or 36 hr. Food-deprived females that were exposed to continuous light for 36 hr showed a significant increase in fetal resorption as compared with food-deprived females exposed to continuous light for 48 hr. Since failure of hypophysial prolactin release appears to be the primary endocrine cause of the inanition-induced implantation failure, the results suggest that exposure to continuous light protects implantation in food-deprived females by stimulating luteotrophic activity.

Fetal loss in mice exposed to magnetic fields during early pregnancy

The effects of low-frequency magnetic fields (MFs) on early pregnancy were studied in CBA/S mice. The magnetic field was a 20 kHz, 15 microT sawtooth. Pregnant females were divided into four groups, two control groups and two exposed groups. One group was exposed to MFs continuously from day 1 postconception (pc) until day 5.5 pc, and the other group was exposed continuously until day 7 pc. All animals were sacrificed on day 19 pc, the day before partus, and their uterine contents were analyzed. No significant increase in the resorption (early fetal death) rate was found in the exposed animals compared to the sham controls. In the group exposed during days 1.0-5.5 pc, the body weight and length of the living fetuses were significantly decreased. Except on day 3 pc (progesterone) and day 13 pc (calcium) in the treated groups, there were no significant differences in progesterone and calcium levels in peripheral blood. Implantation occurred on the same day in MF-treated and control animals.

Opening of the mouse zona pellucida by laser without a micromanipulator

A contact-free laser system is described for ablation of the embryonic mouse zona pellucida using a pulsed excimer 308 nm laser. Effects on further embryonic development were evaluated. Zonae of 8- to 16-cell mouse embryos were either lased (n = 189), zona-drilled with acidified Tyrode's solution (n = 183) or left zona-intact (n = 188). Blastocyst formation (99-100%) was similar in the three groups. Hatching occurred earlier in lased embryos compared to those of the control group. These blastocysts hatched through the laser ablated area. Significantly more embryos were hatching on day 4 in the conventionally drilled group when compared to the laser treated group (50% versus 24% respectively). On day 7 of development, significantly (P < 0.05) more embryos conventionally zona-drilled (37%) were intact than those which were previously laser treated (10%). Abnormal development was also noted in a small group of embryos which were lased just on the outside of the zona in comparison to 1/3 of an embryonic width away from the zona. The current results suggest that apparently precise zona laser ablation with an excimer laser at 308 nm may have potential adverse effects which may only be manifested after a prolonged period of culture past the cavitation stage. However, implantation rates of morphologically normal laser abalated embryos were not impaired when compared to control embryos.

In vitro fertilization, development, and implantation after exposure of mature mouse oocytes to visible light

Mature mouse oocytes were exposed prior to in vitro fertilization to visible light during 1, 2, or 4 hr at an intensity of 4,000 lux. Compared to controls cultured under identical conditions but protected from light, exposed eggs did not show any significant modification of cleavage speed and rate. After transfer of blastocysts obtained in vitro in uteri of pseudopregnant females, the implantation rate and the proportion of normal fetuses were not found to be different in relation to preliminary light exposure of oocytes fertilized and cultured in vitro.

Effects of pre-ovulatory X-irradiation on fertilization, initial cleavage and post-nidation development in the Chinese hamster

In order to investigate the effects of pre-ovulation X-ray radiation on fertilization, initial cleavage and post-nidation development, Chinese hamster dams were mated with normal males after exposure to 200 rads of radiation during the primary maturation period, and cytogenetic studies were performed at 2.5, 3.5 and 10 days after fertilization; comparison studies were also performed on an untreated control group. The results indicated that: (1) The ovarian ova with chromosomal anomalies induced by X-ray radiation had the ability to be fertilized and transmit the abnormality to the 2-celled stage, but most of them deceased by the 8-celled stage. (2) The embryos attaining the 8-celled stage with normal chromosomes were implanted and survived, but showed remarkable hypoplasia on day 10 of gestation.

Effects of AET, MEA, or 5-HT treatment before X-irradiation of pregnant C57BL mice

C57BL++ mice were either whole body X-irradiated with a dose of 200 R or, 15 minutes before X-irradiation injected with AET, MEA, or 5-HT, in a dose of 40 mg/kg of body weight, on the first day of gestation. Uterine contents were examined on the nineteenth day of pregnancy. The number of corpora lutea was assumed as 100% and the percentage values of live and dead foetuses, resorptions, and non-implanted embryos were calculated. The percentage ratio of females with live foetuses in the uterus, in relation to the total number of those with a vaginal plug was also determined. X-irradiation of pregnant mice influenced the embryonic survival. As compared with controls, in only X-irradiated mice a lower percentage value of live foetuses and higher percentage values of non-implanted embryos and resorptions were found. One dead foetus was only observed in X-irradiated females. Percentage value of X-irradiated females with live foetuses was lower than that of control ones. High mortality of embryos occurred more often before than after the implantation of blastocysts. The percentage value of non-implanted embryos was higher than that of resorptions. AET, MEA, and 5-HT when injected to mice before their X-irradiation acted as radioprotectors. The strongest radioprotective effect was obtained following AET administration, intermediate after 5-HT treatment and the weakest one when MEA was injected.

Discrimination between the effects of X-ray irradiation of the mouse oocyte and uterus on the induction of dominant lethals and congenital anomalies. II. Localised irradiation experiments

In order to evaluate whether irradiation of the postimplantation maternal environment contributed to the induction of postimplantation mortality or congenital anomalies, mouse ovaries were surgically exteriorised and selectively irradiated or shielded in a specially constructed apparatus. The results show that exposure of the mouse abdomen and uterus to 3.70 Gy X-rays, 15-21 days prior to conception, has no significant effect on the incidence of either postimplantation mortality or congenital anomalies. Exposure of the ovaries to 3.27 Gy X-rays during the same period, however, increased the frequency of both postimplantation mortality and congenital anomalies.

Discrimination between the effects of X-ray irradiation of the mouse oocyte and uterus on the induction of dominant lethals and congenital anomalies

In order to test whether irradiation of the postimplantation maternal environment had any effect on the apparent induction of dominant lethals or congenital anomalies by radiation, preimplantation embryos were surgically transferred between females which had been irradiated before conception or left untreated. A high proportion of preimplantation embryos, collected from females that had been irradiated 15-21 days prior to conception with 3.6 Gy X-rays, were either arrested or developmentally retarded compared with those collected from untreated females. The transfer experiments indicate that irradiation of the uterus has no significant effect on the frequency of subsequent postimplantation mortality or on mean fetal weight. However, it remains unclear whether irradiation of the uterus contributes to the induction of congenital anomalies.

[Effect of whole-body irradiation of females on pregnancy and postnatal development of the offspring]

In 218 primigravida rats of Wistar strain with body mass 200-250 g radiosensitivity during the whole period of pregnancy has been studied after a single total gamma-radiation with 60Co given in LD50 2.0 Gy. The multifactor analysis includes: dynamics of the body mass of the pregnant rats, ability to implantation and pregnancy, duration of pregnancy, number of births that failed, body mass loss during delivery, death of the embryos during the antenatal period, number of viable offsprings, dynamics of body mass in the offsprings and their viability during 30 days after birth, time for covering with fur and eyes opening, developmental anomalies etc. Quantitative and qualitative postradiative disorders of the intrauterine and postnatal development of the offsprings are described. The most sensitive days of pregnancy are revealed (the 1st--3d and the 9th--11th days).

Induction of congenital malformations in the offspring of male mice treated with X-rays at pre-meiotic and post-meiotic stages

The induction of congenital malformations among the offspring of male mice treated with X-rays at pre-meiotic and post-meiotic stages has been studied in two experiments. Firstly, animals were exposed to varying doses (108-504 cGy) of X-rays and mated at various time intervals (1-7, 8-14, 15-21 and 64-80 days post-irradiation), so as to sample spermatozoa, spermatids and spermatogonial stem cells. In the second experiment, only treated spermatogonial stem cells were sampled. One group of males was given a single 500-cGy dose, a second group a fractionated dose (500 + 500 cGy, 24 h apart) and a third group was left unexposed. In the first experiment, induced post-implantation dominant lethality increased with dose, and was highest in week 3, in line with the known greater radiosensitivity of the early spermatid stage. Preimplantation loss also increased with dose and was highest in week 3. There was no clear induction of either pre-implantation or post-implantation loss at spermatogonial stem cell stages. There was a clear induction of congenital malformations at post-meiotic stages, the overall incidence being 2.0 +/- 0.32% in the irradiated series and 0.24 +/- 0.17% among the controls. The induction was statistically significant at each dose. At the two highest doses the early spermatids (15-21 days) appeared more sensitive than spermatozoa, and at this stage the incidence of malformations increased with dose. The data from Expt. 1 on the induction of malformations by irradiation of spermatogonial stages were equivocal. In contrast, Expt. 2 showed a statistically significant induction of malformations at both dose levels (2.2 +/- 0.46% after 500 cGy and 3.1 +/- 0.57% after 500 + 500 cGy). The relative sensitivities of male stem cells, post-meiotic stages and mature oocytes to the induction of congenital malformations were reasonably similar to their sensitivities for specific-locus mutations, except that the expected enhancing effect of the fractionation regime used was not seen. Dwarfism and exencephaly were the two most commonly observed malformations in all series.

[Effects of small doses of ionizing radiation on embryonic development of the mouse]

Mice with vaginal plugs were irradiated, seven hours after mating, i.e near fecundation, by 5, 10 and 25 rads of gamma rays from a 60Co source. Females were sacrificed on the 18th day of gestation. The total number of implantations was unchanged after exposure to 5 and 10 rads but the frequency of resorptions was increased for all doses. No abnormalities were observed in testicles, kidneys and skeleton.

The effect of short-term labelling in (3H) thymidine on the viability of mouse blastomeres: alone and in combination with unlabelled blastomeres

A method of labelling 8-cell-stage mouse blastomeres with [3H]thymidine is described, which allows them to be followed to the late blastocyst stage and is compatible with normal postimplantation development. However, the [3H]thymidine does affect the postimplantation vigour of the cells when placed in competition with unlabelled cells in blastomere aggregates. This suggests that caution should be used in interpreting results using [3H]thymidine as a label for early mammalian cells.

Increased litter size in the rat x-irradiated during the estrous cycle before mating

Average numbers of ovulations, implantations, and living fetuses obtained from rats x-irradiated during the estrous cycle before mating are a function of both the radiation dose and the time of exposure during the cycle. Animals irradiated during metestrus or the day thereafter exhibit significant increases in the factors studied, while those irradiated on the 3rd day after metestrus maintain fewer implantations after exposure to 300, 500, and 600 roentgens, and fewer living fetuses after exposure to 100 to 600 roentgens.