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101.
Effect of thyroidectomy on cardiovascular responses to hypoxia and tyramine infusion in fetal sheep 总被引:2,自引:0,他引:2
Fetal sheep were thyroidectomized at 80 days' gestation and reoperated at 118-122 days for insertion of vascular catheters. The effects of hypoxaemia and intravenous tyramine infusion on plasma catecholamine concentrations, blood pressure and heart rate were then determined in experiments at 125-135 days' gestation. Age matched intact fetuses were also studied. Thyroidectomy was associated with increased concentrations of noradrenaline, adrenaline and dopamine in some thoracic and abdominal organs, increased noradrenaline concentrations in the cerebellum, and decreased adrenaline concentrations in the hypothalamus, cervical spinal cord, and superior cervical and inferior mesenteric ganglia. Arterial pressure was significantly lower in the thyroidectomized fetuses (34.0 +/- 0.15 mmHg) than in intact fetuses (44.7 +/- 0.2 mmHg; p less than 0.001). In contrast, plasma noradrenaline concentrations were significantly higher in the thyroidectomized fetuses (2.04 +/- 0.25 ng/ml) compared to the intact fetuses (0.99 +/- 0.08 ng/ml; P less than 0.001). In the intact fetuses there was a significant increase in plasma noradrenaline concentration and blood pressure during hypoxaemia, and bradycardia at the onset of hypoxaemia. In contrast, in the thyroidectomized fetuses hypoxaemia did not cause significant change in plasma catecholamine concentrations, blood pressure or heart rate. Infusion of tyramine produced a 1.9-fold increase of plasma noradrenaline in thyroidectomized fetuses compared to a 9.2-fold increase in the intact fetuses (P less than 0.05). Tyramine infusion caused a similar proportional increase of blood pressure in both thyroidectomized and intact fetuses. Heart rate decreased during the tyramine-induced hypertension in the intact fetus, but increased in the thyroidectomized fetuses.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
102.
Youngdo Won Richard A. Friesner Martin R. Johnson Jonathan L. Sessler 《Photosynthesis research》1989,22(3):201-210
The Soret absorption spectra of six synthetic rigid porphyrin dimers whose crystal structures have been determined are simulated using simple exciton theory. The objective is to test the validity of the point dipole and associated approximations; the electronic interaction parameters are thus calculated using data obtained from the monomer spectra, with no adjustable parameters. Satisfactory agreement between theory and experiment is obtained for one class of dimers but not for a second. This poses a challenge for semiempirical electronic structure methods as to whether improvements over the point dipole calculations can be obtained. 相似文献
103.
T. Keshavarz E. Walker R. Eglin G. Lilley G. Holt A. T. Bull M. D. Lilly 《Applied microbiology and biotechnology》1989,30(5):487-491
Summary
Penicillium chrysogenum spores have been immobilized by adsorption on two grades of wet or dry diatomaceous earth particles, Chromosorb-W and Celite R-633. Almost 90% of the spores were adsorbed within 2 h and those remaining in suspension were removed by washing to minimise the growth of free mycelia. After germination the immobilized biomass was almost independent of the spore loading on the particles and whether or not the spore suspension was added to wet or dry particles. The free biomass obtained was less than 5% of the immobilized biomass. 相似文献
104.
During postnatal development, UDP-Gal: GlcNAc(beta 1-4)-galactosyltransferase (4 beta-GT) and UDP-Gal:GalNAc(beta 1-3)-galactosyltransferase (3 beta-GT) activities were increased by 17- and 24-fold, respectively, in the rat small intestine. The injection of cortisone into suckling rats resulted in precocious induction of distal 4 beta- and 3 beta-GT activities by 2.7- and 1.8-fold, respectively. Injection of phorbol-12-myristate-13-acetate (PMA) resulted in precocious induction of distal 3 beta-GT by 2.7-fold. These results suggest that intestinal galactosyltransferase activities are under developmental regulation and can be modified by cortisone and PMA. 相似文献
105.
The culture fluorescence of two recombinant Escherichia coli strains with high plasmid copy number were studied and compared to both the host and low copy number varieties of the corresponding strains. Culture fluorescence data are related to the concentration of reduced intracellular nicotinamide adenine dinucleotide within a cell, and can therefore be used as a means for detecting changes in metabolic states. Correlation curves relating culture fluorescence to biomass show that the recombinant system maintains a larger pool of intracellular NADH at high plasmid copy numbers than either the host or the recombinant system at low copy numbers. These results demonstrate the ability of a fluorescence probe to detect differences in the metabolic demands made on an over-producing recombinant organism. 相似文献
106.
Transposition of the Responder Element (Rsp) of the Segregation Distorter System (Sd) to the X Chromosome in Drosophila Melanogaster 下载免费PDF全文
In order to test whether the meiotic drive system Segregation distorter (SD) can operate on the X chromosome to exclude it from functional sperm, we have transposed the Responder locus (Rsp) to this element. This was accomplished by inducing detachments of a compound-X chromosome in females carrying a Y chromosome bearing a Rsps allele. Six Responder-sensitive-bearing X chromosomes, with kappa values ranging from 0.90 to 1.00, were established as permanent lines. Two of these have been characterized more extensively with respect to various parameters affecting meiotic drive. SD males with a Responder-sensitive X chromosome produce almost exclusively male embryos, while those with a Rsp-Y chromosome produce almost exclusively female embryos. This provides a genetic system of great potential utility for the study of early sex-specific differentiation events as it allows the collection of large numbers of embryos of a given sex. 相似文献
107.
Cell death by apoptosis during involution of the lactating breast in mice and rats 总被引:17,自引:0,他引:17
The role of cell death in involution of lactating breast was investigated in mice and rats by light and electron microscopy. Apoptosis, recognized by sharply demarcated compaction of chromatin against the nuclear envelope and by shrinkage and budding of the whole cell to form membrane-bounded apoptotic bodies, was responsible for major loss of cells in both species. In the mouse, rapid involution during the first 2 days was associated with shedding of large numbers of apoptotic bodies derived from alveolar epithelial cells into alveolar lumens. This was followed by more gradual regression, during which the bodies were mostly phagocytosed by macrophages within the epithelium. In the rat, glandular involution was a more gradual and uniform process, with shedding of apoptotic epithelial cells into alveolar lumens being much less conspicuous. Apoptosis of myoepithelial cells was observed in mice, the resulting apoptotic bodies being phagocytosed by intraepithelial macrophages, but was not detected in rats. Apoptosis of capillary endothelial cells caused rapid regression of the capillary beds in both mice and rats. Intraepithelial macrophages increased in number during involution, developed cytoplasmic lipofuscin pigment, and either remained within the epithelium or migrated to the interstitium and regional nodes. Cell loss by apoptosis has been demonstrated during involution and atrophy of a variety of other glands. It characteristically results in shrinkage of a tissue without disruption of its basic architecture. 相似文献
108.
Two bovine genes for mitochondrial ADP/ATP translocase expressed differences in various tissues 总被引:7,自引:0,他引:7
Two different bovine cDNAs have been characterized that encode closely related homologues of the mitochondrial membrane carrier protein ADP/ATP translocase. One of them codes for the protein that has been characterized previously from bovine heart mitochondria, and the other codes for a protein that differs from it in 33 amino acids out of 297. Including the base substitutions required to bring about these changes in amino acid sequence, the coding regions of the cDNAs differ at 184 positions. In addition, they are extensively diverged in their 3' noncoding sequences, which differ greatly in both length and sequence, and these segments of the cDNAs have been used as hybridization probes to demonstrate that the expression of the two genes giving rise to the two proteins is very different in various bovine tissues. Expression of one gene predominates in heart muscle and that of the other in intestine. Hybridization experiments with digests of genomic DNA have shown the presence of numerous sequences related to the two cDNAs in both the bovine and human genomes. Some of these probably arise from pseudogenes, but three expressed genes have been detected in the human genome. The study of the regulation of the expression of these genes may help to illuminate the basis of tissue-specific human mitochondrial diseases which arise because of defects in mitochondrial enzymes only in the affected tissue and not in other tissues of the same individual. 相似文献
109.
Mitochondrial NADH-ubiquinone reductase: complementary DNA sequences of import precursors of the bovine and human 24-kDa subunit 总被引:4,自引:0,他引:4
The 24-kDa subunit of mitochondrial NADH-ubiquinone reductase (complex I) is an iron-sulfur protein that is present in the flavoprotein or NADH dehydrogenase II subcomplex. It is a nuclear gene product and is imported into the organelle. A group of human patients with mitochondrial myopathy have been shown to have reduced levels of subunits of complex I in skeletal muscle mitochondria, and in one patient the 24-kDa subunit appears to be absent (Schapira et al., 1988). To investigate the genetic basis of this type of myopathy, cDNA clones have been isolated from a bovine library derived from heart and liver mRNA by hybridization with two mixtures of 48 synthetic oligonucleotides 17 bases in length that were designed on the basis of known protein sequences. The recombinant DNA sequence has been determined, and it encodes a precursor of the mature 24-kDa protein. The N terminus of the mature protein is preceded by a presequence of 32 amino acids that has properties that are characteristic of mitochondrial import sequences. The sequence of the mature protein deduced from the cDNA contains a segment of nine amino acids that was not determined in an earlier partial protein sequence analysis. The bovine clone has been employed as a hybridization probe to identify cDNA clones of the human homologue of the 24-kDa protein. Its DNA sequence has also been determined, and it codes for a protein that is closely related to the bovine protein.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
110.
Termination region in rRNA genes from a eucaryotic thermophile, Thermomyces lanuginosus. 总被引:3,自引:0,他引:3 下载免费PDF全文
S1 mapping of the termination region in the ribosomal DNA from a thermophilic fungus, Thermomyces lanuginosus, revealed three distinct termini corresponding to the mature 25S rRNA, a precursor that is 19 nucleotides longer and corresponds to the 37S precursor in yeast cells, and a putative termination site at +96 that bears a limited sequence homology with the SalI box of mammalian cells. An estimate of the secondary structure suggested that the three termini are in close proximity, a feature that may be essential to precursor termination and maturation. The results raise questions regarding recently reported relationships between ribosomal DNA termination and spacer enhancer elements in fungi. 相似文献