Direct exposure of mouse embryonic limb-buds to 5-bromodeoxyuridine in vitro and its effect on chondrogenesis: increasing resistance to the analog at successive stages of development.
(41/9568)
The inhibitory effect of 5-bromodeoxyuridine (BudR) - an analog of thymidine - on embryonic mouse limb-buds was studied in vitro employing an organ-culture system. The effect was found to be dose-related and also depended on the developmental stage of the donor embryos. Limbs at an early stage development (early 11 th-day embryos, somite stage 26-29) were extremely sensitive to the analog. Treatment with low levels (2-4 mug/ml) and for a relatively short period of time in cluture (2-3 days) completely and irreversibly suppressed chondrogenesis in these explants. Limbs from older embryos (somite stage 40 and up) were found to be much less sensitive to the inhibitory effect of the drug; a prolonged exposure to a much higher dose (100-150 mug/ml) resulted in an incomplete suppression of chondrogesesis. Only a 20% inhibition was observed in the cultures of limbs from mid-13th-day mouse embryos. After continuous growth in vitro, the limbs became progressively resistent to the analog and towards the end of the culture period had become refractory to the drug. The time of complete insensitivity appeared earlier in the cures of the limbs taken from older embryos than in the explants of youngerlimbs. These studies show that as limbs continue to differentiate in vivo or in vitro, they become increasingly resistent to the inhibitory effect of BudR in at least as far as the effect on the process of chondrogenesis is concerned. It is suggested that the relative sensitivity or insensitivity to the inhibitory effect of BudR may prove to be a useful parameter in evaluating the developmental stage of an organ. (+info)
Patterns of lactic dehydrogenase isozymes in mouse embryos over the implantation period in vivo and in vitro.
(42/9568)
Following blastocyst implantation, or outgrowth in vitro, the LDH isozyme pattern changes from that of the maternally inherited B subunit isozyme form (LDH-1) to a pattern dominated by A subunits (Auerbach & Brinster, 1967, 1968). In preimplantation embryos we have observed additional isozyme bands, as yet unidentified. An analysis of the pattern of newly synthesized LDH isozymes and specific activity of LDH in different regions of early postimplantation embryos suggests that there is a sequantial activation of A and B subunits, and that activity first appears in ICM- (inner cell mass) derived tissues and then in trophoblast-derived tissues. In vitro, in the absence of ICM cells, the transition of LDH-isozyme pattern does not occur in outgrowing trophoblast giant cells. This suggests a possible inductive interaction between ICM and trophoblast. (+info)
Serum immunoglobulins in aborted and non-aborted bovine foetuses.
(43/9568)
The concentration of immunoglobulin classes G, M and A (IgG, IgM and IgA) in the sera of 233 aborted and 201 non-aborted foetuses was measured. IgM was first detected in a foetus at day 90 of gestation while IgG and IgA were first detected on day 111 of gestation. Immunoglobulins were detected in 81.5% of aborted foetuses and 32.8% of non-aborted foetuses. Total immunoglobulin concentrations of 20 mg/100 ml or greater were found in 35.2% of aborted foetuses but only in 4.5% of non-aborted foetuses. It is suggested that factors resulting in antigenic stimulation of the foetus may play an important part in bovine abortion. (+info)
The nerve supply and conducting system of the human heart at the end of the embryonic period proper.
(44/9568)
The nerve supply and conducting system were studied in a stage 23 human embryo of exceptional histological quality. The nerves on the right side arose from cervical sympathetic and from cervical and thoracic vagal filaments. Out of their interconnexions vagoxympathetic nerves emerged, which (1) sent a branch in front of the trachea to the aorticopulmonary ganglion, thereby supplying arterial and venous structures, and (2) formed the right sinal nerve, which supplied the sinu-atrial node, and gave filaments to the interatrial septum which could be traced to the atrioventricular node and pulmonary veins. The nerves on the left side arose similarly from cervical sympathetic and from cervical and thoracic vagal filaments. These formed several descending, ganglionated, vagosympathetic filaments that descended to the right of the arch of the aorta and entered the aorticopulmonary ganglion. Filaments leaving the ganglion supplied the pulmonary trunk, ascending aorta, interatrial septum, pulmonary veins, and, as the left sinal nerve, the fold of the left vena cava. The thoracic vagal filaments descended to the left of the arch of the aorta and supplied chiefly the arterial end of the heart. No thoracic sympathetic cardiac filaments were found. The sinu-atrial node began as a crescentic mass in front of the lower part of the superior vena cava. It gradually extended on each side of the superior vena cava and came to form its posterior wall at a more caudal level. The atrial myocardium that formed the septum spurium, venous valves, and interatrial septum could be traced from the sinu-atrial to the atrioventricular node. Myocardium also encircled the atrial aspects of the atrioventricular orifices, and could be traced caudally to the atrioventricular nde. The atrioventricular node was a conspicuous mass in the anterior and lower part of the interatrial septum, from which a clearly defined bundle left to enter the interventricular septum. Right and left limbs were observed, the former being a rounded bundle that passed immediately in front of the root of the aorta. (+info)
Perinatal risk and severity of illness in newborns at 6 neonatal intensive care units.
(45/9568)
OBJECTIVES: This multisite study sought to identify (1) any differences in admission risk (defined by gestational age and illness severity) among neonatal intensive care units (NICUs) and (2) obstetric antecedents of newborn illness severity. METHODS: Data on 1476 babies born at a gestational age of less than 32 weeks in 6 perinatal centers were abstracted prospectively. Newborn illness severity was measured with the Score for Neonatal Acute Physiology. Regression models were constructed to predict scores as a function of perinatal risk factors. RESULTS: The sites differed by several obstetric case-mix characteristics. Of these, only gestational age, small for gestational age. White race, and severe congenital anomalies were associated with higher scores. Antenatal corticosteroids, low Apgar scores, and neonatal hypothermia also affected illness severity. At 2 sites, higher mean severity could not be explained by case mix. CONCLUSIONS: Obstetric events and perinatal practices affect newborn illness severity. These risk factors differ among perinatal centers and are associated with elevated illness severity at some sites. Outcomes of NICU care may be affected by antecedent events and perinatal practices. (+info)
Pregnant rat uterus expresses high levels of the type 3 iodothyronine deiodinase.
(46/9568)
Although thyroid hormones are critically important for the coordination of morphogenic processes in the fetus and neonate, premature exposure of the embryo to levels of the hormones present in the adult is detrimental and can result in growth retardation, malformations, and even death. We report here that the pregnant rat uterus expresses extremely high levels of the type 3 iodothyronine deiodinase (D3), which inactivates thyroxine and 3,3', 5-triiodothyronine by 5-deiodination. Both D3 mRNA and activity were present at the implantation site as early as gestational day 9 (E9), when expression was localized using in situ hybridization to uterine mesometrial and antimesometrial decidual tissue. At later stages of gestation, uterine D3 activity remained very high, and the levels exceeded those observed in the placenta and in fetal tissues. After days E12 and E13, as decidual tissues regressed, D3 expression became localized to the epithelial cells lining the recanalized uterine lumen that surrounds the fetal cavity. These findings strongly suggest that the pregnant uterus, in addition to the placenta, plays a critical role in determining the level of exposure of the fetus to maternal thyroid hormones. (+info)
Expression of cyclo-oxygenase types-1 and -2 in human fetal membranes throughout pregnancy.
(47/9568)
Human labour is associated with increased prostaglandin synthesis within the fetal membranes. We have studied the expression of the two isoforms of the central prostaglandin synthetic enzyme, cyclo-oxygenase (COX-1 and COX-2), in human fetal membranes throughout pregnancy, at mRNA, protein and activity levels. COX-1 mRNA expression was low in human amnion and chorion-decidua and did not change with gestational age. COX-2 mRNA expression in fetal membranes increased with gestational age, with significant up-regulation prior to the onset of labour and in association with labour. Protein concentrations of COX-1 did not change, whilst concentrations of COX-2 increased from the first to the third trimester. COX activity increased with gestational age and in association with labour, although prostaglandin production in fetal membranes collected after labour was reduced, suggesting reduced substrate supply. These data suggest that it is up-regulation of COX-2, rather than of COX-1, which mediates increased prostaglandin synthesis within the fetal membranes at term. Much of the increase in COX-2 expression precedes the onset of labour, suggesting that it is a cause, rather than a consequence, of labour. (+info)
Oxytocin receptor expression in human term and preterm gestational tissues prior to and following the onset of labour.
(48/9568)
Oxytocin receptor (OTR) mRNA expression has previously been demonstrated in human myometrium, decidua, chorion and amnion but the effect of gestational age and the onset of labour has not been determined in these individual tissues. Spatial OTR mRNA expression was examined by in situ hybridization and ligand binding was confirmed using autoradiography with the iodinated oxytocin antagonist d(CH2)5[Tyr(Me)2,Thr4,Tyr-NH29]-vasotocin (125I-OTA). Tissue was collected at term (>37 weeks of gestation) or preterm (24-36 weeks of gestation) caesarean section and classified as labour (contractions every 5 min associated with cervical dilatation) or non-labour. OTR mRNA expression was measured as optical density units from autoradiographs. There was a highly significant (P<0.001) effect of tissue type on expression of OTR mRNA with expression greatest in myometrium, low in decidua and chorion and not detected in placenta. Similar results were obtained with the 125I-OTA-binding studies, indicating that the message was translated. Amnion had an apparently high level of both hybridization and 125I-OTA binding in some samples, but a lack of specificity prevented quantification of the signal in this tissue type. Term myometrium (labour and non-labour) had significantly higher (P<0.01) OTR mRNA expression than preterm myometrium, but there was no further increase in mRNA concentration associated with labour onset. In contrast, 125I-OTA binding in myometrium was already high at 33 weeks and did not increase further either later in pregnancy or with labour. In decidua there was no effect of gestational age or labour onset on OTR mRNA expression or 125I-OTA binding. In summary, OTR mRNA expression in the myometrium increased in late pregnancy whereas decidual expression was much lower and did not rise at term. (+info)