9 results
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2. Weightlessness and the developing frog egg.
- Author
-
Young RS and Tremor JW
- Subjects
- Animals, Embryo, Nonmammalian physiology, Larva, Time Factors, Cleavage Stage, Ovum physiology, Embryonic Development, Rana pipiens embryology, Space Flight, Weightlessness
- Abstract
This paper describes the results of the flight of fertilized frog eggs in the manned orbital flights Gemini 8 and Gemini 12. The experiment was designed to determine the effect of weightlessness or near weightlessness on the ability of the cell to divide normally and on subsequent differentiation and embryogenesis. Eggs were fixed periodically in flight so that recovered material could be carefully compared to simultaneous ground controls with respect to gross morphology and histology. Some embryos were recovered alive after 4 days in orbit. In general, no abnormalities were detected which were inconsistent with the controls. Death, shortly after recovery, of the embryos recovered alive in Gemini 12, remains unexplained. The protocol of the experiment and the experimental hardware is described. Rationale for future experiments is discussed.
- Published
- 1968
3. Influence of steroid replacement therapy on rat embryos of hypophysectomised mother animals.
- Author
-
Köhler, E., Berswordt-Wallrabe, R., Ehmke, W., and Wojnorowicz, F.
- Abstract
The effects of estrone plus progesterone on embryonic survival were studied in hypophysectomised pregnant rats. Replacement therapy commenced 24 h prior to the ablation of the pituitary which was performed on day 6 of pregnancy. The number of viable fetuses was correlated with increasing amounts of progesterone from 24 to 84 mg/kg given in concert with a constant dose of 4 μg/kg estrone. As judged by the DNA content of the 14-day-old embryos, growth retardation was linked to the reduction of the progesterone levels. No visible malformations were recorded although the experimental period covered the phase of organogenesis. On the other hand, when measuring in isolated nuclei of 14-day-old rat embryos the activity of DNA polymerase, an enzyme the activity of which can be correlated to a certain extent to embryonic growth, it becomes obvious that after treatment with estrone in combination with low (24 or 36 mg/kg) or too high doses (84 mg/kg) of progesterone the correlation between DNA content of the embryos and DNA polymerase activity per cell diverges. This result may point to a cellular malfunction not disclosed by the macroscopic appearance of the embryos at this stage. So it can be concluded that embryonic growth and differentiation processes might be directly dependent on maternal gonadal hormones, at least till day 12 of pregnancy. [ABSTRACT FROM AUTHOR]
- Published
- 1971
- Full Text
- View/download PDF
4. The Indirect Effect of Irradiation on Embryonic Development
- Author
-
Mary M. McLaughlin and Robert L. Brent
- Subjects
business.industry ,Embryogenesis ,Embryonic Development ,Mothers ,Congenital malformations ,Bioinformatics ,Embryonic stem cell ,Indirect effect ,Toxicology ,Fetus ,Pregnancy ,Medicine ,Female ,Irradiation ,business - Abstract
Introduction Many factors contribute to the production of congenital malformations. It is the job of the experimentalist to decide what is their relative importance and to uncover all the contributing factors and their interrelationships. This same philosophy applies to congenital malformations caused by one etiology, namely, irradiation. The factors responsible for radiation teratogenesis are multiple and interrelated. Any classification would be completely arbitrary. For the purposes of this paper, the role of radiation can be thought of as mediated directly through the embryo, and indirectly through irradiation of the placenta and/or mother. It is the purpose of this and the subsequent paper to decide on how important these so-called indirect effects are in radiation teratogenesis, and not to determine the nature of these effects. Previous to the work of Wilson, Karr, Jordan, and Brent, all pregnant mammals were given whole-body irradiation, and therefore the direct and indirect factors could not
- Published
- 1960
5. A test for mutagenicity of caffeine in mice
- Author
-
Lyon, Mary F., Phillips, Rita J. S., and Searle, A. G.
- Published
- 1962
- Full Text
- View/download PDF
6. Studies on the teratogenic phase specificity of actinomycin D in the rat
- Author
-
Köhler, E. and Merker, H. -J.
- Published
- 1972
- Full Text
- View/download PDF
7. Hormonal Steroid Contraceptives IV: Adverse Reactions and Management of the Patient
- Author
-
McQueen, E. G.
- Published
- 1971
- Full Text
- View/download PDF
8. End-product repression in the creatine pathway of the developing chick embryo
- Author
-
James B. Walker
- Subjects
Cancer Research ,medicine.medical_specialty ,Normal diet ,Arginine ,Embryonic Development ,Chick Embryo ,Biology ,Kidney ,Creatine ,Guanidines ,Enzyme Repression ,chemistry.chemical_compound ,Transferases ,Internal medicine ,Genetics ,medicine ,Animals ,Enzyme Inhibitors ,Molecular Biology ,Psychological repression ,Guanidine ,Derepression ,Methionine ,Research ,Rats ,Endocrinology ,Liver ,Gluconeogenesis ,Biochemistry ,chemistry ,Creatinine ,Molecular Medicine - Abstract
Negative feedback systems are believed to be operative in higher animals in physiologically important processes ranging from formation of tropic hormones to maintenance of organ size. However, model systems for the study of such controls at the molecular level in intact animals are quite rare, and are limited to two biosynthetic pathways: the cholesterol-bile acid pathway, and the creatine pathway. In this paper the properties of the latter model system are described in detail. Two enzymes are involved in the biosynthesis of creatine. The second enzyme appears to be constitutive, whereas the steady-state level of the first enzyme, arginine-glycine transamidinase, is responsive to the tissue concentration of creatine. This process has been operationally termed end-product repression, by analogy with bacterial systems, until its mechanism can be more completely elucidated. Creatine repression of transamidinase has been observed in the rat, mouse, rabbit, chick, and duck, in tissues as diverse as kidney, pancreas, and liver. More recently, repression has been studied in the liver of the developing chick embryo and the newly hatched chick. Virtually complete repression of embryonic liver transamidinase can be maintained throughout development by a single injection of creatine into the egg. Derepression occurs in the first week following birth, when chicks are fed a normal diet. Numerous experiments have shown that there is a highly specific relationship between the target enzyme and the controlling compound. Creatine precursors proximal to the target enzyme repress 35–50 per cent while the precursor distal to the target enzyme represses completely. In the closed system of the egg, repression of the target enzyme can be readily shown to be proportional to repressor concentration. Moreover, this system permits the demonstration that repression can occur in the absence of intestinal flora, and under conditions of minimal hormonal influences. The normal pattern of change of transamidinase activity during embryonic and neonatal development is consistent with a repression by endogenous creatine prior to birth, followed by a post-hatch derepression, but other explanations are also entertained. Evidence is cited in support of the thesis that the creatine-transamidinase control system has survival value for birds, and perhaps reptiles and amphibians. It is suggested that liver transamidinase of carnivorous birds is normally in a partially repressed state, as a result of the 0·4 per cent creatine content of ingested muscle tissue, whereas transamidinase of herbivorous birds is normally derepressed. Experimentally it has been demonstrated that fasting lowers the activity of both the repressed and derepressed enzymes. At least part of this decrease can be attributed to a repression by endogenous creatine which appears in increased concentration in the blood, liver and kidneys of most higher animals during fasting. During fasting, then, the decrease in transamidinase activity permits diversion of a portion of the dietary essential amino acids, arginine, glycine, and methionine, from the synthesis of creatine, now in excess, to more immediately essential biosyntheses. For example, glycine is essential for synthesis of the uric acid required to remove amino groups arising from the gluconeogenesis of fasting; methionine methyl groups are required for the increased lipid transport of fasting; and all three amino acids are needed for synthesis of essential enzymes, protein hormones, and feathers. In addition to the foregoing, the implications of the occurrence of a repressible system during embryonic development for the problem of the establishment and maintenance of tissue-specific enzyme levels are discussed.
- Published
- 1963
9. Weightlessness and the developing frog egg
- Author
-
R S, Young and J W, Tremor
- Subjects
Embryo, Nonmammalian ,Time Factors ,Weightlessness ,Cleavage Stage, Ovum ,Larva ,Rana pipiens ,Animals ,Embryonic Development ,Space Flight - Abstract
This paper describes the results of the flight of fertilized frog eggs in the manned orbital flights Gemini 8 and Gemini 12. The experiment was designed to determine the effect of weightlessness or near weightlessness on the ability of the cell to divide normally and on subsequent differentiation and embryogenesis. Eggs were fixed periodically in flight so that recovered material could be carefully compared to simultaneous ground controls with respect to gross morphology and histology. Some embryos were recovered alive after 4 days in orbit. In general, no abnormalities were detected which were inconsistent with the controls. Death, shortly after recovery, of the embryos recovered alive in Gemini 12, remains unexplained. The protocol of the experiment and the experimental hardware is described. Rationale for future experiments is discussed.
- Published
- 1968
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