ISSN:0040-3709    

DOI:10.1002/tera.1420450602

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

ISSN:0040-3709    

DOI:10.1002/tera.1420450603

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractA theoretical basis for the embyology of conjoined twins was formulated from clinical experience with ten cases and extensive review of pertinent embryologic and clinical literature, including over 500 cases. Regarding the age old question offusion or fission, it is concluded that there is no known embryologic process by which conjoined twins can be formed by fission but firm evidence to support fusion in all cases. Whether the fusion occurs between embryos on one embryonic disc or on two is of no consequence since they are all monovular. Intact ectoderm will not fuse to intact ectoderm, and all seven types of conjoined twins are explained by seven possible sites of union in the early embryo. One new term is proposed:parapagus, from the Greekpara, meaning “side,” combined withpagus, meaning “fixed”; this is the group formerly called dicephalus or diprosopos. These anterolaterally united parapagus twins must result from two nearly parallel notochords in close proximity; craniopagi and pygopagi from fusion at the cranial and caudal neuropores, respectively; cephalopagi and ischiopagi from union at the pharyngeal and cloacal membranes, respectively; thoracopagi from merging of the cardiac anlage; and omphalopagi from fusion of the umbilicus or of the edges of two embryonic discs in any area not including the above sites. Parasitic twins result from embryonic death of one twin, leaving various portions of the body vascularized by the surviving autosite.The rarity of cases (2) not easily explained by the above theories, and the nearly 6% of twins with two umbilical cords arising from the placenta would seem to support these conclusions.Should one wish to learn the methods of a conjurer, he might vainly watch the latter's customary repertoire, and, so long as everything went smoothly, might never obtain a clue to the mysterious performance, baffled by the precision of the manipulations and the complexity of the apparatus; if, however, a single error were made in any part or if a single deviation from the customary method should force the manipulator along an unaccustomed path, it would give the investigator an opportunity to obtain a part or the whole of the secret. Thus … it seems likely that through the study of the abnormal or unusual some insight may be obtained into that mystery of mysteries, the development of an organism … especially … where the abnormalities … are due to some modification in the germ itself, leading the organism to develop in accordance with laws as definite and natural, though not as usual, as those governing normal development (Wilder, '08). © 1992

ISSN:0040-3709    

DOI:10.1002/tera.1420450604

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractStudies on teratogenicity and pathology of the cenceptus were conducted in Sprague‐Dawley rats treated with 600, 800, and 1,000 mg/kg valproic acid po on day 13 of pregnancy. Each of the three doses was maternotoxic and caused (1) resorptions and/or abortions, reduction in the number of live fetuses per litter and mean fetal weight, and defects of the tail, rib and phalanx; and (2) degenerative changes in the labyrinth (thrombosis, angiectasis in the maternal lacunar network, necrosis of cytotrophoblasts and suppressed proliferation of fetal capillaries), reduced diameter nearing obliteration of umbilical vessels, with or without karyorrhexis of embryonic tissues. The lesions in the placental labyrinth were specific but, in the embryonic tissues, they were generalized. It was postulated that the vascular lesions in the labyrinth and umbilicus may have influenced embryonic development by reducing maternoembryonic gaseous and nutritional exchange. © 1992 Wiley‐Liss,

ISSN:0040-3709    

DOI:10.1002/tera.1420450605

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractHistologic changes in extraembryonic and embryonic tissues induced by 3 or 6 μg 2,3,7,8‐tetrachlorodibenzo‐p‐dioxin/kg (TCDD) or 80 μg 2,3,4,7,8‐pentachlorodibenzofuran/kg/day (4‐PeCDF) were studied 24 h after the last of four daily doses administered orally to C57BL/6N mice on days 10‐13 of pregnancy. Both test compounds ruptured (1) the embryo‐maternal vascular barrier in the labyrinth, which resulted in hemorrhage of embryonic blood into the maternal circulation, (2) the visceral yolk sac membrane with the embryonic blood from the vitelline vessels escaping into the uterine, exocelomic and amniotic cavities, and (3) the maternal vascular spaces of the placental periphery resulting in hemorrhages into the interconceptal space. The role of the hemorrhagic lesions in the induction of cleft palate and hydronephrosis by the two compounds remains to be investigated. The presence of embryonic nucleated erythroblasts that hemorrhaged into the maternal lacunar network allowed the identification of maternal venous channels in the placenta. It revealed that (1) the labyrinth could be tentatively divided into two caudocranially oriented zones, an arterial and a venous zone; (2) the maternal blood in the labyrinthine lacunae circulated from the arterial to the venous zone, somewhat parallel to the uterine axis; and (3) the largest maternal vessels in the center of the placenta hitherto named the “central maternal artery,” was in fact, venous. ©

ISSN:0040-3709    

DOI:10.1002/tera.1420450606

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractIn order to evaluate the teratogenic potential of acetazolamide in rabbits, three groups of 18 artificially inseminated females were treated orally with 50, 100, or 150 mg/kg/day of acetazolamide on days 6‐18 of gestation. These doses induced maternal acidosis and electrolyte changes, consistent with those reported in rats and considered to be a result of carbonic anhydrase inhibition, as well as reductions in maternal body weight gain. At cesarean sections, average fetal body weights in the acetazolamide groups were dosedependently decreased compared with controls. There were no effects of acetazolamide on embryonic survival or external morphology of live fetuses. In the fetal skeletal examination, thoracic and lumbar vertebral malformations occurred in 0.7%, 3.9%, and 6.1% of fetuses in the 50, 100, and 150 mg/kg/day groups, respectively, compared with none in the control group. In addition, missing vertebra was seen in a small number of fetuses in the 100 and 150 mg/kg/day groups. These axial skeletal malformations were, in some cases, associated with costal malformations. These results indicate that acetazolamide at maternotoxic doses can produce axial skeletal malformations in the rabbit. © 1992 Wiley‐Liss,

ISSN:0040-3709    

DOI:10.1002/tera.1420450607

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractCertain synthetic retinoids differ widely from retinoic acid (RA) in teratogenic potency, being much more or much less effective than RA. It is assumed that the potency of a retinoid may depend on the nature of its interaction with cellular binding components (nuclear retinoic acid receptors or cytoplasmic binding proteins) and, as in the case of retinoids that are mammalian teratogens, on factors that determine its accessibility to the embryo. To investigate some of the factors that contribute to potency, we used a new synthetic retinoid Ro 13‐6307 that differs in structure from RA in having an aromatic ring inserted in its side chain along with gem dimethyl modification of the natural cyclohexenyl ring. Pregnant ICR mice were given a single oral dose (0, 1, or 10 mg/kg) on day 11 of gestation, and the resultant teratogenic outcome was monitored on day 17. Direct effects on cell differentiation were obtained by exposing high density cultures of limb bud mesenchymal cells to a range of concentrations (0.3 ng/ml‐3 μg/ml) of Ro 13‐6307 and scoring for chondrogenic suppression. Concentrations reaching the embryo after maternal administration of Ro 13‐6307 were measured by HPLC to quantify the analog for a period of 4 h after administration of the oral dose. We found that this retinoid was 40‐fold as active as RA in both inducing teratogenesis and suppressing chondrogenesis, yet its concentration in the affected embryo was only a fraction of that achieved after an equivalent dose of RA was employed in a similar protocol. Since the morphogenetic activity of Ro 13‐6307 is disproportionately in excess of its levels in the mouse embryo, obligatory mediation by the receptors or by other binding proteins, or both, is likely involved. © 1992 Wi

ISSN:0040-3709    

DOI:10.1002/tera.1420450608

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractResearch suggests that, perhaps through mechanisms initiated by vasoconstriction and leading to vessel thrombosis or embolism, cocaine causes vascular disruption defects, and that frequent cocaine use during early pregnancy could disrupt multiple organ systems in the fetus. We hypothesized that if cocaine is an important cause of multiple vascular disruption defects, a rising prevalence of cocaine use by mothers during pregnancy should be accompanied by rising rates of these defects in their offspring. Using data from the Metropolitan Atlanta Congenital Defects Program, we identified all infants born in Atlanta from 1968 through 1989 who had nonsyndromic, provisional vascular disruption defects affecting more than one organ system: 61 infants (78%) had gastrointestinal and genitourinary defects, 7 (9%) had gastrointestinal and abdominal wall defects, 2 (3%) had gastrointestinal and limb reduction defects, 2 (3%) had limb reduction and abdominal wall defects, 2 (3%) had central nervous system and gastrointestinal defects, 2 (3%) had genitourinary and limb reduction defects, 1 (1%) had genitourinary and abdominal wall defects, and 1 (1%) had central nervous system and genitourinary defects. The prevalence of Atlanta infants with more than one vascular disruption defect is 0.13 per 1,000 live births. Chi‐square analysis for trends showed no increase in prevalence during the study period. Our data are from one of the first population‐based studies in which trends for defects potentially caused by maternal cocaine use are examined; the results of our study show no significant change in the prevalence of multiple vascular disruption defects over time. We suspect that if cocaine is a teratogen, its teratogenicity is weak or is associated with a small subset of birth defects that are yet to be identified. © 1992 Wiley‐Lis

ISSN:0040-3709    

DOI:10.1002/tera.1420450609

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractWe previously showed that digit formation in mouse embryos from early morning mating seemed to progress faster than those from overnight mating. In this study, to confirm this phenomenon, we examine whether the embryos from normal (0 hr from ovulation to fertilization) and delayed matings (3, 6, or 9 hr from ovulation to fertilization) respond differently to some acute teratogens when they are treated at the same time point from mating.Five mg/kg of cytosine arabinoside (Ara‐C) was given to pregnant mice intraperitoneally at 246, 249, or 252 hr (day of gestation (dg) 10) after mating. The patterns of Ara‐C induced digit malformations in embryos from the delayed mating groups were those of more advanced stages, when compared with normal mating groups with the same time intervals from mating to Ara‐C treatment. In other words, oocytes fertilized up to 9 hr after the presumed time of ovulation could grow similarly to those of normally fertilized oocytes. Thiscatch‐up phenomenonsuggests that theovulation clockshould be used for the startpoint of the time scale of the growth and differentiation of embryos rather thanfertilization clock. © 1992 Wiley

ISSN:0040-3709    

DOI:10.1002/tera.1420450610

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractRat embryos at a single gestational time in the presomite period were studied for their variation in development and their fate after culture. They were explanted at 8 A.M. on day 9 of gestation from timed‐pregnant Sprague‐Dawley rats which were obtained by mating between 8 and 10 A.M. (plug day = day 0). In the first experiment, a total of 203 embryos from 20 litters were examined for their variation in development. Several dimensions of embryo/egg cylinder were measured and development of various embryonic/extraembryonic structures were assessed using a scoring system that we developed for the present study. Embryos were then divided into different stages of development based on their scores using the staging system that we developed previously. A large variation in developmental stage was demonstrated; the youngest embryo was at the early primitive streak stage with no signs of amniotic folds and the oldest one was at the late neural plate stage with a foregut pocket but without visible somites. No strong correlation was demonstrated between developmental stage and size of embryo/egg cylinder, nor between developmental stage and development of the proamniotic tube, ectoplacental cavity, or allantois. In the second experiment, embryos were explanted at the same time and those at different stages were cultured separately in rotating bottles and their outcomes were compared after 49 hours. The difference in mean somites number of embryos cultured from the mid primitive streak and late neural plate stages was 6.1. This difference corresponds to approximately 10 hours based on the known linear increase of somites number on day 11 of approximately 0.6 somites per hour. These results indicate a large variation in development of presomite period embryos supposedly of the same gestational age and suggest the importance of careful staging at the time of explantation if precision is needed for whole embryo culture experiments. © 1992 Wiley‐Lis

ISSN:0040-3709    

DOI:10.1002/tera.1420450611

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY