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Twenty ovariectomized ewes were used in an experiment designed to examine the interaction of progesterone, estradiol, and oxytocin in the regulation of uterine secretion of prostaglandin F2 alpha (PGF2 alpha). All ewes underwent a steroid pretreatment that mimicked the changes in progesterone and estradiol which occur during the six days immediately prior to estrus. After pretreatment, ewes were randomly assigned to 1 of 4 treatment groups: 1) control (n = 4); 2) estradiol-17 beta (n = 6); 3) progesterone (n = 4); and 4) progesterone and estradiol-17 beta (n = 6). Progesterone was injected twice daily for 15 days. The dose of progesterone varied with day postestrus in a manner designed to simulate endogenous luteal secretion of progesterone. Estradiol-17 beta was administered in s.c. Silastic implants. The implants maintained circulating concentrations of estradiol at 3 pg/ml. On Days 5, 10, and 15 of treatment, ewes were injected with oxytocin (10 IU in 1.0 ml saline, i.v.). Jugular venous blood samples were collected beginning one-half hour prior to and continuing for 2 hours post-oxytocin injection for quantification of 13,14-dihydro-15-keto-prostaglandin F2 alpha (PGFM). No changes in concentration of PGFM following injection of oxytocin were observed on Day 5 or 10 in any treatment group. Concentrations of PGFM increased following injection of oxytocin on Day 15 only in groups receiving progesterone. Both the area under the PGFM response curve (p = 0.08) and peak response (p = 0.06) were greater in ewes treated with progesterone and estradiol-17 beta than in those receiving progesterone alone.(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   
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The kinetics of haemolysis of rabbit erythrocytes byCroton tiglium lectin was studied as a function of concentration of the lectin and erythrocytes. The length of the prelytic period decreased with increasing lectin concentrations, indicating that the secondary events at the membrane which follow the binding of the lectin to cell surface carbohydrate receptors are accelerated at higher surface concentrations of the lectin. The rate or extent of haemolysis was not affected by the inclusion of ions like K+, Ca2+ and Mg2+ in the medium or by the substitution of ionic medium by a non-ionic medium. The inhibition of haemagglutination and haemolysis of rabbit red cells byCroton tiglium lectin by antilectin rabbit serum was observed. A possible mechanism of haemolysis by the lectin is discussed.  相似文献   
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N-Acetyl-D-galactosamine in β-linkage being ubiquitous in cell surface glycoproteins, their interaction with lectins specific for this sugar moiety may be a significant event in cell adhesion phenomena. This article discusses the common β-N-acetyl galactosamine-specific lectins, with particular stress on the lectin from winged beans (Psophocarpus tetragonolobus).  相似文献   
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A PROCESS called “excitation-contraction coupling” has been generally accepted to take place only in the direction of excitation to contraction. Through this mechanism a propagated action potential initiates an active state in skeletal or cardiac muscle and the muscle contracts. We propose that, in the mammalian ventricular myocardium at least, the process is not unidirectional and an important reverse coupling between the contractile system and the excitable plasma membrane has been overlooked. Through this feedback interaction the mode of contraction (that is, isotonic or isometric) not only determines the instantaneous electrical state of the plasma membrane, but also influences the mechanical events of the subsequent beats. Thus when Kaufmann et al.1 recorded intracellular action potentials from cat papillary muscle, the time course of the repolarization was altered depending on the mode of contraction. Some kind of contraction-excitation feedback has also been suggested by Stauch2 and Lab3,4. They showed a difference in the shape of the monophasic action potential, as recorded by a suction electrode, when comparing isotonic and isovolumic contraction of the intact ventricle. But their experimental conditions did not allow satisfactory analysis of the phenomenon.  相似文献   
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Sokawa et al. suggest that rel- strains of Escherichia coli possess abnormal protein synthesizing machinery, which cannot carry out normal protein synthesis when the supply of amino-acids is limited.  相似文献   
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A hypothesis has been developed to relate stringent control in bacteria to a set of interactions involved in the regulation of growth of transformed and untransformed mammalian cells.  相似文献   
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