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K Hardy

Publications and source records attributed to K Hardy.

At least 91 records · Page 5Linked to original sources
PubMed1992

Description, analysis and impact of major solar activity during recent U.S. Shuttle missions.

Since STS-26, three large solar events have occurred during Shuttle missions; a geomagnetic storm during STS-29 and solar particle events (SPEs) during STS-28 and -34. The maximum dose to a crew attributed to an SPE was estimated to be 30 microGy (70 microSv). Time-resolved dosimetry measurements of the SPE dose during STS-28 were made using the Air Force Radiation Monitoring Equipment (RME)-III. Comparison of calculated and measured dose demonstrated a discrepancy, possibly a result of deficiencies in the geomagnetic cutoff model used. This experience demonstrates that dose from an SPE is strongly dependent on numerous factors such as orbit inclination, SPE start time, spectral parameters and geomagnetic field conditions; the exact combination of these factors is fortuitous. New sources of data and procedures are being investigated, including real-time tracking of auroral oval positions or determination of particle cutoff latitudes, for incorporation into operational Shuttle radiation support practices.

Cosmic Radiation↗
PubMed1992

BABI in dispute.

Explore the source record for details and available documents.

Blastomeres↗
PubMed1992

Biopsy of cleavage stage human embryos and diagnosis of single gene defects by DNA amplification.

Preimplantation diagnosis offers an alternative to current prenatal diagnostic techniques for patients known to be at risk of transmitting an inherited disease. One or two cells can be removed from cleavage stage embryos from patients undergoing in vitro fertilization. Affected embryos can be identified by analyzing the cells for the defect using the polymerase chain reaction. Following analysis, embryos identified as unaffected are replaced in the patient. The identification and transfer of female embryos was attempted in eight couples known to be at risk of transmitting various X-linked diseases. Five of the eight women became pregnant, two with twin and three with singleton pregnancies, after a total of 13 treatment cycles. Six of the seven fetuses were confirmed as being female after chorionic villus sampling. The prospects for the specific diagnosis of single gene defects are described.

Biopsy↗
PubMed1991

Hypoxanthine phosphoribosyl transferase deficiency, haematopoiesis and fertility in the mouse.

We have looked for effects of deficiency in hypoxanthine phosphoribosyl transferase (HPRT) in the mouse comparable to non-behavioural consequences of HPRT-deficiency in humans. HPRT-deficient humans show abnormalities in haematopoiesis and, in heterozygotes, there is strong selection in haematopoietic tissues against HPRT-deficient cells arising as a result of X-chromosome inactivation. We have examined two situations in mice in which HPRT- and HPRT+ cells occur in the same individual. First, in chimaeras resulting from the injection of HPRT- embryonal stem cells into HPRT+ blastocysts the fate of HPRT- and HPRT+ cell populations was monitored by their expression of different isozymes of glucose phosphate isomerase and also, in those chimaeras that resulted from injecting the male ES cells into female blastocysts, by in situ hybridisation using a Y-chromosome-specific repetitive DNA probe. There was a small statistically significant selection against the HPRT- population in haematopoietic tissues in both XX in equilibrium with XY and XY in equilibrium with XY chimaeras. Second, in female mice doubly heterozygous for HPRT-deficiency and for an electrophoretic variant of the X-linked enzyme phosphoglycerate kinase, there was a similar small statistically significant selection against the HPRT- population in haematopoietic tissues. While further work is required to establish whether this selection is a consequence of the HPRT mutation, it is clear that any selection against cells in the haematopoietic system as a consequence of HPRT-deficiency is at most small compared with the effect seen in humans. In HPRT-deficient human males surviving beyond the normal age of puberty, there is testicular atrophy. However, we find no effect of HPRT-deficiency on the fertility of either male or female mice. Thus, as with effects on behaviour, the consequences of HPRT-deficiency for haematopoiesis and testis development in the mouse are at most small compared with those in the human. We conclude that the reason for the difference in effects between the two species lies in a difference in purine-related intermediary metabolism per se, rather than in its interaction with brain amine biochemistry.

Animals↗
PubMed1991

Sex chimaerism, fertility and sex determination in the mouse.

Adult intraspecific mouse chimaeras, derived by introducing male embryonal stem cells into unsexed host blastocysts, were examined to determine whether gonadal sex was correlated with the sex chromosome composition of particular cell lineages. The fertility of XX in equilibrium XY and XY in equilibrium XY male chimaeras was also compared. The distribution of XX and XY cells in 34 XX in equilibrium XY ovaries, testes and ovotestes was determined by in situ hybridisation using a Y-chromosome-specific probe. Both XX and XY cells were found in all gonadal somatic tissues but Sertoli cells were predominantly XY and granulosa cells predominantly XX. The sex chromosome composition of the tunica albuginea and testicular surface epithelium could not, in general, be fully resolved, owing to diminished hybridisation efficiency in these tissues, but the ovarian surface epithelium (which like the testicular surface epithelium derives from the coelomic epithelium) was predominantly XX. These findings show that the claim that Sertoli cells were exclusively XY, on which some previous models of gonadal sex determination were based, was incorrect, and indicate instead that in the mechanism of Sertoli cell determination there is a step in which XX cells can be recruited. However, it remains to be established whether the sex chromosome constitution of the coelomic epithelium lineage plays a causal role in gonadal sex determination. Male chimaeras with XX in equilibrium XY testes were either sterile or less fertile than chimaeras with testes composed entirely of XY cells. This impaired fertility was associated with the loss of XY germ cells in atrophic seminiferous tubules. Since this progressive lesion was correlated with a high proportion of XX Leydig cells, we suggest that XX Leydig cells are functionally defective, and unable to support spermatogenesis.

Animals↗
PubMed1991

Profiles of hypoxanthine guanine phosphoribosyl transferase and adenine phosphoribosyl transferase activities measured in single preimplantation human embryos by high-performance liquid chromatography.

The profiles of hypoxanthine guanine phosphoribosyl transferase (HGPRT) and adenine phosphoribosyl transferase (APRT) activities were examined in normally fertilized human embryos developing at the normal rate in vitro between the 2-4-cell stage on Day 2 and the blastocyst stage on Day 6 after insemination. The activities of both enzymes were assayed simultaneously in extracts of single embryos by measuring the rate of production of the reaction products, inosine monophosphate (IMP) and adenine monophosphate (AMP), separated by high-performance liquid chromatography (HPLC). The activity profiles of the two enzymes over this period showed marked differences. The activity of HGPRT, coded by the X chromosome, increased between Days 2 and 4 (P less than 0.01) but declined sharply by Day 6 (P less than 0.001), whereas autosome-coded APRT activity remained low between Days 2 and 5, but increased on Day 6 (P less than 0.05). The profile of HGPRT activity may reflect a combination of decreasing levels of maternal enzyme inherited from the oocyte and the initiation of embryonic gene expression followed by X inactivation at the blastocyst stage on Day 6.

Adenine Phosphoribosyltransferase↗
PubMed1990

Pregnancies from biopsied human preimplantation embryos sexed by Y-specific DNA amplification.

Over 200 recessive X chromosome-linked diseases, typically affecting only hemizygous males, have been identified. In many of these, prenatal diagnosis is possible by chorion villus sampling (CVS) or amniocentesis, followed by cytogenetic, biochemical or molecular analysis of the cells recovered from the conceptus. In others, the only alternative is to determine the sex of the fetus. If the fetus is affected by the defect or is male, abortion can be offered. Diagnosis of genetic defects in preimplantation embryos would allow those unaffected to be identified and transferred to the uterus. Here we report the first established pregnancies using this procedure, in two couples known to be at risk of transmitting adrenoleukodystrophy and X-linked mental retardation. Two female embryos were transferred after in vitro fertilization (IVF), biopsy of a single cell at the six- to eight-cell stage, and sexing by DNA amplification of a Y chromosome-specific repeat sequence. Both women are confirmed as carrying normal female twins.

Base Sequence↗
PubMed1990

Extragonadal teratocarcinoma derived from embryonal stem cells in chimaeric mice.

Three tumours which arose in two (one male and one hermaphrodite) out of 63 chimaeric mice resulting from injection of E14TG2a embryo stem (ES) cells into host blastocysts have been investigated. All of the tumours appeared within the first 3 weeks after birth. The tumour in the male chimaera and one of the tumours in the hermaphrodite were in the perigenital region but were extragonadal. The third, smaller tumour in the hermaphrodite was on the caecum. The perigenital tumour in the male chimaera was a teratocarcinoma with a wide variety of differentiated tissues, including non-pigmented retina, as well as nests of undifferentiated embryonal carcinoma (EC) cells with high levels of alkaline phosphatase activity. The perigenital tumour in the hermaphrodite was a teratoma, less differentiated and with no evidence of EC cells. Glucose phosphate isomerase isozyme analysis indicated that both perigenital tumours were predominantly of the injected ES cell rather than the host blastocyst type. The possible origins of these tumours, which are the first reported to have arisen from ES cells in chimaeric mice, are discussed.

Abdominal Neoplasms↗
PubMed1990

Pulmonary lobar transplantation in neonatal swine: a model for treatment of congenital diaphragmatic hernia.

Congenital diaphragmatic hernia (CDH) babies born with severe pulmonary hypoplasia are unsalvageable despite maximal therapy including extracorporeal membrane oxygenation (ECMO). Lung transplantation is a potential treatment for these otherwise doomed infants using ECMO as a bridge to transplantation. Cadaveric, or living related donation of a more mature reduced size lung (pulmonary lobe or segment) may help solve the critical donor shortage problem. We evaluated the physiological response of mature left lower lobe (LLL) transplants in neonatal swine with the hemodynamic conditions of CDH simulated by occlusion of the right pulmonary artery (PA), and also studied the pulmonary function of the mature lobar graft compared with the neonatal lung. LLL transplantation was well tolerated and resulted in minimal alteration in hemodynamic parameters. The response to right PA occlusion was similar pre- and posttransplantation with a fall in cardiac output and a significant rise in pulmonary vascular resistance. Compared with the contralateral native lung, the lobar graft was preferentially ventilated with resultant higher pH (7.65 +/- 0.17 v 7.41 +/- 0.08, P less than .01) and lower pCO2 (17 +/- 6 v 36 +/- 5, P less than .001). The more mature lobar graft was preferentially ventilated due to the increased compliance compared with the neonatal right lung (8.16 +/- 1.28 v 5.48 +/- 0.82 mL/cm, P less than .0001). Reduced size lung transplantation is technically feasible and may help solve the donor problem for severe CDH neonates for whom no effective therapy is currently available.

Animals↗
PubMed1990

Non-invasive measurement of pyruvate and glucose uptake and lactate production by single human preimplantation embryos.

The consumption of pyruvate and glucose and the production of lactate by 40 single human preimplantation embryos has been measured using a non-invasive technique. Twelve of the embryos showed abnormal fertilization. Of the 28 normally fertilized embryos, nine (32%) developed to the blastocyst stage in culture while the remainder degenerated or arrested during cleavage. In the normal embryos, pyruvate uptake exceeded that of glucose in the early developmental stages (days 2-5 post-insemination) before glucose became the predominant substrate in the blastocyst (day 6). Considerable quantities of lactate were formed throughout development, rising from a value of 43.6 pmol/embryo/h on day 2.5 to 95.4 pmol/embryo/h on day 5.5. The values of pyruvate and glucose uptake and lactate production of those embryos which arrested were below those which developed normally. On the basis that one mole of glucose can give rise to two moles of lactate, only 50% of the lactate produced could be accounted for in terms of glucose uptake from the medium. This figure rose to 90% in the blastocyst. The remaining lactate must be derived from endogenous sources, most probably glycogen. It is proposed that the high production of lactate by human preimplantation embryos in vitro is an adaptation to the conditions of culture.

Blastocyst↗
PubMed1990

Human preimplantation development in vitro is not adversely affected by biopsy at the 8-cell stage.

Normally fertilized human embryos biopsied 3 days after in-vitro fertilization (IVF) have been examined for effects on viability and development in vitro after removal of one or two cells at the 8-cell stage (1/8 and 2/8) from each embryo. A high proportion of 7/8 and 6/8 biopsied and unmanipulated embryos developed to the blastocyst stage between days 5 and 6 (79, 71 and 59%, respectively), and many biopsied embryos (56%) hatched from the zona pellucida in vitro. The viability of biopsied embryos which developed to the blastocyst stage was assessed by daily non-invasive measurement of the uptake of two energy substrates, glucose and pyruvate. Uptake of both substrates was generally lower in 7/8 and 6/8 biopsied embryos but only in proportion to the reduced cellular mass. The total cell number and the numbers of both trophectoderm (TE) and inner cell mass (ICM) cells in biopsied embryos at the blastocyst stage, counted by differential labelling of their nuclei, were also reduced in proportion but the ratio of ICM to TE cells was maintained in both 7/8 and 6/8 biopsied embryos. We conclude that removal of one or two cells at the 8-cell stage, while reducing the cellular mass, does not adversely affect the preimplantation/development of biopsied embryos in vitro and suggest that this approach could be used for preimplantation diagnosis of genetic defects.

Biopsy↗
PubMed1990

Tracheobronchial obstructions in infants and children. Experience with 45 cases.

Forty-five infants and children with intrathoracic tracheobronchial obstructions requiring surgical treatment are reported. Segmental stenosis of the trachea is defined as involvement of less than one half the length of the airway, which affected six infants. Elongated stenosis involving more than one half the length of the trachea was seen in 12 infants, and complete annular cartilage rings, along the entire length of the trachea, were present in 11. Severe tracheomalacia occurred in six infants associated with aortic arch anomalies and in nine infants with esophageal atresia. Segmental tracheal resection was performed in 17 cases (two after failure of a rib cartilage graft), and anastomotic stricture developed in three. These three anastomotic strictures were resected, resulting in an excellent airway in two and restricture in one. Rib cartilage grafts were used in five patients: two of three with elongated stenosis with complete tracheal rings required subsequent resection, and one of two infants with tracheomalacia had excellent outcome. Approximately 50% of an infant's trachea can be resected, but rib cartilage grafts should be used for elongated stenosis. Resection of bronchial stenosis in two patients resulted in a widely patent bronchus. From this experience primary segmental tracheobronchial resection and re-resection of recurrent stenosis are highly successful. Anastomotic stricture is due to tension at the suture line and suture material inciting a fibrotic reaction. Rib cartilage grafts amounting to 25% or less of the circumference of the airway readily resurfaces with adjacent epithelium, but when 30% or more of the circumference is rib graft, epithelialization may be impaired.

Bronchial Diseases↗
PubMed1989

Genetic analysis of DNA from single human oocytes: a model for preimplantation diagnosis of cystic fibrosis.

Gene sequences in human oocytes were studied to investigate the possibility of diagnosing inherited or sporadic genetic disease before implantation after in vitro fertilisation. By specific amplification the possibility of analysing the DNA from single human oocytes for a specific gene was shown, and genotypes for markers closely linked to cystic fibrosis and Duchenne muscular dystrophy were determined. Single oocytes were used to approximate the total amount of DNA present in a single cell taken for biopsy from a 4-16 cell blastocyst. With a new technique for specific DNA amplification, the polymerase chain reaction, these data can be obtained within several hours of cell isolation. Extreme care must be taken to avoid any contamination of the sample with DNA from other sources. With this technique genotyping for single gene disorders is feasible with an accuracy and on a time scale that would allow implantation of the zygote after in vitro fertilisation without freezing.

Base Sequence↗
PubMed1989

Non-invasive measurement of glucose and pyruvate uptake by individual human oocytes and preimplantation embryos.

Pyruvate and glucose uptake by 73 individual human oocytes and preimplantation embryos was measured non-invasively, using an ultramicrofluorescence assay to analyse changes in substrate levels in microdroplets of culture medium. The uptake of both substrates was measured over successive daily incubations between days 1 (unfertilized oocytes) or 2 ('spare' embryos which were not transferred) and day 6 (day 0 = day of insemination). Under these conditions, 58% (25/43) of fertilized embryos with two pronuclei on day 1 developed to the blastocyst stage by day 6. The pyruvate uptake of these embryos increased from approximately 28 to a maximum of 40 pmol/embryo/h between days 2.5 and 4.5. Similarly, glucose uptake increased from approximately 8 to 14 pmol/embryo/h between days 2.5 and 4.5, but then increased further to 24 pmol/embryo/h on day 5 at the blastocyst stage. [corrected] The pyruvate uptake of fertilized embryos which arrested at cleavage stages was significantly lower than for those which developed to the blastocyst stage. Polyspermic and parthenogenetic embryos, and unfertilized oocytes also had lower pyruvate uptakes at later stages. The glucose uptake of unfertilized oocytes and abnormal embryos never reached the level of fertilized embryos at the blastocyst stage on day 5.5. Non-invasive measurement of pyruvate uptake before embryo transfer may provide a valuable functional criterion for the selection of viable embryos capable of developing to the blastocyst stage.

Blastocyst↗