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381.
V. Pli<ska 《Cellular and molecular life sciences : CMLS》1991,47(3):216-221
Summary Binding studies in various biological systems frequently indicate the presence of several binding sites for a biologically active ligand. They differ in their affinity for the ligand in question, binding capacity, and Hill coefficient, which suggests differences in the mechanisms of the binding site-ligand interactions. Identification of the true receptors (sites initiating a cellular response) appears to be difficult. Three clusters of binding sites for oxytocin were found on rat myometrial cells. The oxytocin receptor seems to be linked to the medium-affinity site; the cooperation between the high-and medium-affinity sites in eliciting the uterotonic response seems likely, but lacks experimental proof. Dose-response analysis in partially irreversibly inhibited uterus preparations, the method of equipotent doses (Furchgott-Bursztyn method), and structure-activity analysis of oxytocin-like peptides acting as competitive inhibitors of oxytocin, turned out to be suitable for pharmacological analysis of this receptor system. 相似文献
382.
383.
Summary Tamoxifen is an anticancer drug widely used in the treatment of estrogen-dependent breast cancer. In hatchling alligators it acts as a pure antiestrogen in that it completely blocks the effect of estradiol-induced oviductal hypertrophy and completely blocks the estradiol-induced hepatic vitellogenin secretion. Paradoxically, when injected into alligator eggs incubated at 33°C, a temperature which would normally result in 100% male hatchlings, tamoxifen sex reverses the embryos into apparently normal female hatchlings. 相似文献
384.
Summary Normal human spermatozoa were demonstrated by dot immunoblot analysis and immunohistochemistry to possess transglutaminase (TGase). The immunological identification of spermatozoal TGase is consistent with reports by others of its biochemical identification and suggested role in sperm motility,and provides, in view of the immunoregulatory properties of seminal plasma TGase, presumptive identification of a means whereby spermatozoa, under normal physiological conditions, may possibly be protected from immunological attack within the female reproductive tract. 相似文献
385.
Summary An ectomycorrhiza, a specialized root organ, is the result of a complex interaction leading to a finely-tuned symbiosis between a plant and a compatible ectomycorrhizal fungus. Ultrastructural observations combined with cytochemical and biochemical studies reveal that structural and metabolic changes in the symbiont cells lead to the final phenotype of the active ectomycorrhiza. In the present review these changes are interpreted as changes in gene expression and discussed within the context of ectomycorrhiza development. Recent genetic data indicate that the continued vegetative growth of the ectomycorrhizal hyphae and the root tissues, and their ability to switch to symbiotic organ formation, is basically controlled by developmentally critical genes. The activity of these symbiotic genes during the differentiation of ectomycorrhizas is associated with extensive changes in the concentration of particular polypeptides and protein biosynthesis. The present state of knowledge about the developmental biology of ectomycorrhizas allows only speculation about the events during their development.Puisant mes forces aux sources des galaxies En buvant la sève des arbres M. Jonasz 相似文献
386.
Fenton F. Robb 《Systemic Practice and Action Research》1990,3(4):389-399
As there would be appear to be no limit to the process of successive emergence, the emergence of suprahuman autopoietic systems seems possible, if not yet necessary. Maybe there really are constraints on human behavior which would not permit such entities to emerge, or maybe the emergence of such entities entails the dissipation of more free energy than available at present. But unless such conditions are present, then, it appears to me, the emergence of suprahuman autopoietic systems is not just probable, it is inevitable.In any event, whether or not they share my concern about suprahuman autopoietic systems, all concerned with metaphor manufacture should attend to this important insight from Swenson (1989a, b, c, d) and should not be deterred by my so inadequate reflection of a new and important view of how the organizational world works. 相似文献
387.
Summary The biochemical development of the fetal brain in relation to maternal vitamin A restriction was studied in rats. The vitamin A status of pregnant rats was varied by supplying low, medium and adequate amounts (6, 40, and 100 g retinol/day/kg body weight, respectively) of vitamin A during pregnancy and suckling. The maternal vitamin A restriction caused an altered brain development in terms of tissue weight, DNA, RNA and protein levels, and biosynthesis of DNA and protein from [3H]-thymidine and [3H]-leucine, respectively. A dose-dependent effect of maternal vitamin A restriction on the metabolism of DNA, RNA and protein was noticed in the developing fetal brain of rats. 相似文献
388.
Summary N-acyl dehydroalanines react with and scavenge mainly superoxide radical
and hydroxyl radical (HO.). The ortho-methoxyphenylacetyl dehydroalanine derivative, indexed as AD-20, protects mice against damage resulting from total body X-irradiation, as measured by the increase in their survival time. AD-20 increases the LD50 at 30 days from 6.1 to 7.3 Gy in animals exposed to a wide range of X-rays (6 to 10 Gy). The dose reduction factor (D R F) of AD-20 is 1.20. We postulate that such radioprotective effect may result from its free radical scavenging activity. 相似文献
389.
Summary The ability of liposomes composed of different kinds of phospholipid materials to adhere to the surface of the cornea was studied in the rabbit. The liposomes were labelled with tracer amounts of an I125-labelled phosphatidylethanolamine derivative and were instilled in 10 l drops onto the cornea. The retention of radioactivity was monitored. The results show that liposomes containing positively charged phospholipids are better retained than an albumin control. Thus, it may be possible to develop a drug delivery, liposome system which would permit long-term sustained release of ophthalmic drugs onto the cornea. 相似文献
390.
Summary The in vitro absorption of calcium from the duodenum was significantly less in a group of rats fed on a wheat diet than in a group fed a wheat and Bengal gram (7030) diet. 相似文献