Human fetuses

Cortisol-Cortisone Conversion. Under normal conditions, this equilibrium slightly favors the oxidized compound. Similarly, the conversion of corticosterone to 11-deoxycorticosterone is also mediated by the liP-hydroxysteroid dehydrogenase enzyme system and requites NAD(P) /NAD(P)H. This conversion is especially important both in the protection of the human fetus from excessive glucocorticoid exposure, and in the protection of distal nephron mineral ocorticoid receptors from glucocorticoid exposure (14). The impairment of this conversion is thought to result in hypertension associated with renal insufficiency (15). 

There is positive evidence of risk to the human fetus. 

The POMC protein is processed differendy in the anterior lobe than in the intermediate lobe. The intermediate lobe of the pituitary is mdimentary in adult humans, but it is active in human fetuses and in pregnant women during late gestation and is also active in many animal species. Processing of the POMC protein in the peripheral tissues (gut, placenta, male reproductive tract) resem-... 

Boehm N., Roos J. and Gasser B. (1994). LHRH-expressing cells in the nasal septum of human fetuses. Dev Br Res 82, 175-180. 

Chuah M. and Zheng D. (1987). Olfactory marker protein is present in olfactory receptor cells of human fetuses. Neuroscience 23, 363-370. 

Ortmann R. (1988). Uber Sinneszellen am fetalen vomeronasalen organ der Menschen (receptor cells in the vomeronasal (Jacobson s) organ in the human fetus). HNO 37, 191-197. 

Quinton H.W., Grant W., Thrasivoulou C.Q. and Besser G.M. (1997). Gonadotropin-releasing hormone immunoreactivity in the nasal epithelia of adults with Kallmann s syndrome and isolated hypogonadotropic hypogonadism, in the early midtrimester human fetus. J Clin Endocrinol Metab 82, 309-314. 

Schaal B., Marlier L. and Soussignan R. (1998). Olfactory function in the human fetus evidence from selective neonatal responsiveness to the odor of amniotic fluid. Behav Neurosci 112, 1438-1449. 

Schaal B., Orgeur P. and Rognon C. (1995). Odor sensing in the human fetus anatomical, functional and chemo-ecological bases. In Prenatal Development Psychobiological Perspectives (Krasnegor N.A., Fifer W.A. and Smotherman W.P., eds.). L. Erlbaum Ass, Hillsdale, N.J. 

Smith T.D., Siegel M.I., Mooney M.P., Burdi A.R., et al. (1996). Vomeronasal organ growth and development in normal, and cleft-lip and palate, human fetuses. Cleft Palate-Craniofac J 33, 385-394. 

Takahashi S., Iwanaga T Takahashi Y., Nakano Y., et al. (1984). Neuron-specific enolase, neurofilament protein and S-100 protein protein in the olfactory mucosa of human fetuses an immunohistochemical study. Cell Tiss Res 238, 231-234. 

Yukimatsu M., Takami S., Matsumura G. and Nishiyama F. (2000). Immunoreactivity for G-proteins in the vomeronasal organ of human fetuses. Chem Senses 25, 215 (abs. P-17). 

Lutein and zeaxanthin are the dominant carotenoids in nonretinal eye tissue, and lycopene and p-carotene have been found in the ciliary body, which after the retina and the retinal pigment epithelium (RPE) contains the highest quantity of carotenoids (Bernstein et al. 2001). The orbital adipose tissue also contains measurable quantities of lutein and p-carotene, and possibly other carotenoids as minor constituents (Sires et al. 2001). It is also interesting to note that lutein was recently identified in the vitreous body of human fetuses, 15-28 weeks old (Yakovleva et al. 2007). However, these results may have to be considered with caution, because the vitreous bodies were described as substantially being penetrated with hyaloid blood vessels, which could have contaminated the vitreous with blood. 

Myometrium of pregnancy is a unique example of visceral smooth muscle. Essentially quiet for the majority of gestation, a burst of rhythmic contractile activity is responsible for delivery of the human fetus. Endocrine signals originating from the fetus are likely responsible for the events that begin labour (McLean Smith 2001), but the mechanisms of intra- and intercellular signalling during the course of labour are not fully resolved. 

Figure 1. Total amounts and rate of accretion of calcium and phosphorus in the body of the human fetus with gestation. (Reproduced with permission from Ref. 1. Copyright 1965 W. B. Saunders Company.)...

Participant selection and exclusion criteria — including justification of the use of special participant populations, such as children, pregnant women, human fetuses, and neonates or the mentally handicapped — are appropriately established. 

Li Y, Yokoi T, Kitamura R, Sasaki M, Gunji M, et al. 1996. Establishment of transgenic mice carrying human fetus-specific CYP3A7. Arch Biochem Biophys 329 235-240. 

Schaal, B., Marlier, L., and Soussignan, R. (2000). Human fetuses learn odours from their pregnant mother s diet. Chemical Senses 25,729-737. 

Comparative Toxicokinetics. Metabolic pathways and mechanisms of hepatotoxicity of carbon tetrachloride have been the subject of many studies in intact animals and in vitro, and are therefore better understood than for many other chemicals. However, there are apparently no data on metabolism of carbon tetrachloride in humans. It would be valuable to conduct in vitro experiments with human liver samples and hepatocytes to determine whether metabolic pathways and toxic metabolites are similar to those found in animals. It would also be beneficial to identify an animal model in which MFO systems develop in uteroas they do in the human fetus. 

Adverse effects are uncommon although diarrhea and abdominal cramping in up to 30% of patients may limit its use. Misoprostol should be avoided in pregnant subjects and women of childbearing potential should be advised of adequate contraception as misoprostol may cause miscarriage. Effects on the developing human fetus are not known. 

These hormones induce amphibian metamorphosis, the change of a tadpole into a frog—an obviously very complex series of biochemical and developmental reactions. Human fetuses will show skeletal abnormalities as well as neuromuscular and mental retardation if born with an inadequately functioning thyroid gland. 

Sex helps to remove deleterious mutations from a population.243 A large fraction of human fetuses (at least 10-25%) contain an "incorrect" number of chromosomes and as many as 20% of oocytes are defective. In contrast only 3-4% of sperm are chromosomally abnormal. Female meiosis I appears to be highly error-prone.243a Abnormal fertilized eggs or embryos are eliminated later in development. 

Zinc was confirmed as essential for humans in 1936 and deficiency symptoms were reported in l%l. The size of ihe human fetus is correlated with zinc concentration in the amnintic fluid and habitual low zinc intake in the pregnant female is thought to he related (o several congenital anomalies in humans. Low zinc intakes result in hypogonadism, dwarfism. mental retardation, low serum and red blood cell zinc in humans and animals, and retarded growth and teratogenic effects on the nervous system in rats. 

Since animal studies suggested the possibility of fetal and neonatal malformations it has for a long time been customary to exclude pregnancy before giving tamoxifen. However, there is currently reason to believe that the risk presented by tamoxifen to the human fetus is very slight or non-existent. 

Developmental Effects. Based on the existing information, it is not known whether silver causes developmental toxicity in humans. No studies were found concerning developmental effects in humans after exposure to silver. However, a human study by Robkin et al. (1973) did investigate the possibility of a relationship between the concentration of this heavy metal in the tissue of fetuses and the occurrence of developmental abnormalities. These authors reported that the concentration of silver in the fetal liver of 12 anencephalic human fetuses was higher (0.75 0.15 mg/kg) than the values from 12 fetuses obtained either through therapeutic abortions (0.23 0.05 mg/kg), or in 14 spontaneously aborted fetuses (0.21 0.05 mg/kg). The concentration in 9 premature infants was 0.68 0.22 mg/kg. The authors could not determine if the higher concentrations of silver in anencephalic fetuses were associated with the malformation, or with fetal age. 

There is nothing to suggest that the human BBB is not at least equally well formed at birth than it is in the rat. Occludin and claudin-5 expression is detected in the capillary endothelium of the brain of the 14 week human fetus, and it has the same pericellular distribution as seen in the adult [72]. Pioneering studies by Grontoft [73] in stillborn human fetuses from approximately 12 week gestation and perinatal deaths have demonstrated a postmortem BBB to trypan blue present from at least the start of the second trimester, which is comparable to that of the adult human. 

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