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Biomedical subjects

R K Christenson

Publications and source records attributed to R K Christenson.

125 records · Page 7Linked to original sources
PubMed1977

Gluconeogenesis from alanine in vivo by the ovine fetus and lamb.

Gluconeogenesis from alanine was determined with an intravenous infusion of [U-14C]alanine and [6-3H]glucose or [U-14C]glucose in five fetal lambs (3.6 +/- 0.1 kg; 127 days of gestation) and four growing ewe lambs (37 +/- 2 kg). Conversion of alanine to glucose (mmol/h) was 0.40 +/- 0.12 and 0.51 +/- 0.10 and accounted for 7.3 and 25.6% of the alanine turnover in fetal and growing lambs, respectively. Alanine contributed 2.3 and 1.1% of the glucose turnover and 22.3 and 1.1% of the lactate turnover in fetal and growing lambs, respectively. Lactate contributed 19.5% of the glucose turnover in growing lambs, and glucose synthesis from lactate accounted for 24.7% of the lactate turnover. Glucose turnover (mmol/h) was 10.2 and 25.1 in fetal and growing lambs, respectively. Results from these studies have shown that the fetal lamb at 127 days of gestation has a high rate of alanine turnover and conversion to glucose when compared with that of the growing lamb on a high plane of nutrition.

Alanine↗
PubMedDate not supplied

Analysis of transcriptional control elements in the 5'-upstream region of ovine interferon-tau gene using feeder-independent caprine trophoblast cell line, HTS-1.

Interferon-tau (IFNtau) is a protein secreted from the embryonic trophectoderm of ruminant ungulates during peri-implantation period. This protein acts on the uterine endometrium, which indirectly maintains corpus luteum function, and is therefore considered essential for the process of maternal recognition of pregnancy. Transcriptional regulation of IFNtau genes had been examined using human choriocarcinoma cell lines, JEG-3 or JAR, however, molecular mechanisms by which cell and term specific IFNtau expression are regulated have not been elucidated. Recently, a feeder cell free-trophoblast cell line derived from Shiba-goat placenta, termed HTS-1, was established. In the present investigation, the 5'-upstream region of ovine IFNtau (oIFNtau) gene was analysed using this cell line, which would provide a more suitable system for studies of the ovine trophoblast specific gene than human choriocarcinoma cells. Variously modified 5'-upstream sequences of the oIFNtau gene fused to a luciferase reporter gene were transiently transfected into HTS-1 cells, and human JEG-3 cells were used as a control. These results and co-transfection with expression vectors revealed that Ets-2 binding site in the promoter region was important in HTS-1, whereas AP-1 that binds to the enhancer region was a major activator in JEG-3. By electrophoretic mobility shift assay, a nuclear protein from HTS-1 cells was confirmed to bind specifically to the Ets-2 site of oIFNtau promoter region. Differences in amounts of AP-1 and Ets-2 protein were demonstrated in nuclear extracts from HTS-1, JEG-3 and ovine conceptuses. Substantial differences on oIFNtau gene transcriptions found between caprine HTS-1 and human JEG-3 cells suggest that this cell line could be valuable in the elucidation of a molecular mechanism(s) by which oIFNtau gene expression is regulated in a cell specific manner.

5' Flanking Region↗
PubMedDate not supplied

Detection of transforming growth factor-alpha and epidermal growth factor receptor mRNA and immunohistochemical localization of their proteins in the ovine uterus during the early implantation period.

Accumulated evidence suggests that growth factors of the epidermal growth factor (EGF) family play an important role in the murine implantation process. In the sheep, however, the uterine distribution of these factors and their receptor, EGF receptor (EGF-R), during implantation is not known. This study examined the presence of mRNA transcripts and immunohistochemical localization for transforming growth factor-alpha (TGF-alpha), the potent EGF-family member, and EGF-R in the ovine uterus during the early implantation period. By reverse transcriptase-polymerase chain reaction and sequencing of the products, the presence of TGF-alpha and EGF-R mRNA transcripts were detected in the endometrium on Days 14, 16 and 20 (Day 0 = day of mating). Immunohistochemical analysis revealed that the luminal and glandular epithelial cells and some stromal cells of the endometrium and the trophectoderm were positive for TGF-alpha and EGF-R on Days 14 and 15. Distinct staining for TGF-alpha was observed in the glandular epithelium of deep endometrial areas and strong immunoreactivity for EGF-R was found in the trophectoderm. On Days 16, 18 and 20, although the staining pattern for TGF-alpha was similar to that on the previous days, the immunoreactivity for EGF-R in the stromal cells increased and that in the gland decreased. A distinct immunoreactivity for EGF-R was found in the trophectoderm throughout the days examined. These results suggest that TGF-alpha expressed in the endometrium and trophectoderm may exert effects locally on these tissues during implantation in sheep. Furthermore, it is speculated that the temporal changes in the uterine EGF-R distribution may be related to the endometrial microvascular development.

Animals↗