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This review examines the evidence that skeletal muscles can sense the status of the peripheral vascular network through group III and IV muscle afferent fibers. The anatomic and neurophysiological basis for such a mechanism is the following: 1) a significant portion of group III and IV afferent fibers have been found in the vicinity and the adventitia of the arterioles and the venules; 2) both of these groups of afferent fibers can respond to mechanical stimuli; 3) a population of group III and IV fibers stimulated during muscle contraction has been found to be inhibited to various degrees by arterial occlusion; and 4) more recently, direct evidence has been obtained showing that a part of the group IV muscle afferent fibers is stimulated by venous occlusion and by injection of vasodilatory agents. The physiological relevance of sensing local distension of the vascular network at venular level in the muscles is clearly different from that of the large veins, since the former can directly monitor the degree of tissue perfusion. The possible involvement of this sensing mechanism in respiratory control is discussed mainly in the light of the ventilatory effects of peripheral vascular occlusions during and after muscular exercise. It is proposed that this regulatory system anticipates the chemical changes that would occur in the arterial blood during increased metabolic load and attempts to minimize them by adjusting the level of ventilation to the level of muscle perfusion, thus matching the magnitudes of the peripheral and pulmonary gas exchange. 相似文献
13.
Bruno Lunelli 《Inorganica chimica acta》2007,360(3):1217-1220
A new purification procedure exploiting the simultaneous presence of a solid, liquid, and gas phase in a low surface area system is proposed and discussed. The assumptions of vanishingly low diffusion coefficients in the solid phase and that of the presence of a single “effective impurity” allow to plan the sequence of operations starting from the knowledge of just the melting and boiling points of the substance to be purified and of those of the “effective impurity”. Examples and results are presented. 相似文献
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6(5)carboxyfluorescein (6(5)CF), a polar fluorescein with an apparent pK of 6.3, was introduced, as a pH 6.3 solution, into the apoplast of lamina or petioles of mature soybean leaves. Freehand sections were prepared at various times and immediately observed with a fluorescence microscope. 6(5)CF-associated fluorescence appeared in all sink organs, from shoot apex to roots. It was strictly confined to the phloem regions, even after 4 days. Its transport into young leaves ceased at approximately the time they underwent sink-to-source transition. It was never transported between two leaflets of the same leaf. Its transport was interrupted by phloem destruction. All these transport characteristics were highly reproducible, and were paralleled by those of 14C transport after application of (14C)sucrose to leaf surfaces. In contrast with 6(5)CF, fluorescein was transported between mature leaves, and between leaflets of the same leaf. It was not restricted to phloem, and often appeared in the xylem region. These results indicate that 6(5)CF can be used to monitor phloem sap translocation in real time, in short- and long-term experiments. 相似文献
16.
Data on mortality among over 8000 Canadians aged 35 to 79 years who participated in the Nutrition Canada survey are presented. The effects of various risk factors on mortality were assessed with a multivariate Poisson regression analysis. Factors associated with a significantly increased risk of death over a 10-year follow-up period ending in 1981 included cigarette smoking, hypertension and diabetes mellitus. A shallow U-shaped mortality pattern was observed for body mass index and for serum cholesterol level. No statistically significant increases in risk were associated with alcohol consumption. The population attributable risks for smoking, hypertension and diabetes were 39%, 8% and 6% respectively for men and 21%, 12% and 7% respectively for women. 相似文献
17.
Bruno Peruzzo Sara Rodríguez Luis Delannoy Silvia Hein Prof. Estéban M. Rodríguez Andreas Oksche 《Cell and tissue research》1987,247(2):367-376
Summary The massa caudalis of the subcommissural organ-Reissner's fiber complex of lamprey larvae (Geotria australis) was studied immunocytochemically at the ultrastructural level by use of the immunoperoxidase-silver methenamine procedure. An antiserum raised against bovine Reissner's fiber was utilized as primary antibody.The caudalmost portion of the central canal and its ampulla caudalis communicate, via wide intercellular spaces in their dorsal wall, with large cavities or lacunae. In addition, distinct openings in the dorsal wall of the ampulla establish an open communication between the latter and the lacunae. The lacunae are lined by slender processes of cells of unknown nature. No junctional complexes can be observed between these cells, which lack a basal lamina. The lacunae communicate with structures resembling blood capillaries, however, they are devoid of a basal lamina. These peculiar vessels, in turn, are in direct communication with characteristic blood capillaries.Reissner's fiber (RF) and its massa caudalis are strongly immunoreactive with the antiserum used. The wide intercellular spaces in the dorsal wall of the central canal and the ampulla, as well as the lumina of the (i) lacunae, (ii) modified vessels and (iii) blood capillaries are filled with a flocculent, strongly immunoreactive material. No immunoreactive material was found outside these structures. Thus, the blood capillaries appear to represent the only final target of RF-material arriving at the ampulla caudalis.Supported by Grant I 38259 from the Stiftung Volkswagenwerk, Federal Republic of Germany, Grant S-85-39 from the Dirección de Investigaciones, Universidad Austral de Chile, and Grant 6027 from Fondo Nacional de Desarrollo Científico y Tecnológico, Chile. The authors express their gratitude to Mrs. Elizabeth Santibáñez and Mr. Julio Lamilla for providing the lamprey larvae and to Mr. Humberto Molina for preparing the three-dimensional drawing 相似文献
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On choice of substrate and habitat in brachionid rotifers 总被引:9,自引:9,他引:0
Information on the distribution of 28 rotifers of the family Brachionidae from diverse waters in south and central Sweden was analyzed to reveal their relationships to substrate and habitat. Some brachionids are preferably planktic, others periphytic and/or benthic. Some non-planktic habitats are utilized more than others, but there is no evidence of a chemical attraction from any substrate. Instead, some substrates seem to be avoided, possibly depending on a poorer flora of periphytic algae. Besides substrate type, the following factors are found to be important for creating separate ecological niches in the brachionid family: temperature, oxygen content, trophic degree, chemical environment, food choice and sensitivity to predation. It is possible to delineate separate ecological niches for all brachionid rotifers, implying that Hutchinson's ideas about the plankton paradox are contradicted. Some species are specialists, other are generalists, the latter being characterized by a great morphological variation. The species are adapted in different ways to their preferential habitats, as regards foot, egg-carrying, protrusions and other lorical structures etc. Longer spines, for instance, are generally found in more transparent water, being a supposed protection against visual predators. 相似文献
20.
Bruno Schwarzkopf Brigitte Reuke Andreas Kiener Adelbert Bacher 《Archives of microbiology》1990,153(3):259-263
Growing cultures of Methanobacterium thermoautotrophicum were supplemented with [U-14C]adenosine or [1-14C]adenosine. 7,8-Didemethyl-8-hydroxy-5-deazariboflavin (factor F0) and 7-methylpterin were isolated from the culture medium. Hydrolysis of cellular RNA yielded purine and pyrimidine nucleotides. The ribose side chain of proffered adenosine is efficiently incorporated into cellular adenosine and guanosine nucleotide pools but not into pyrimidine nucleotides. Thus, M. thermoautotrophicum can utilize exogenous adenosine by direct phosphorylation without hydrolysis of the glycosidic bond, and AMP can be efficiently converted to GMP. Factor F0 and 7-methylpterin had approximately the same specific activities as the purine nucleotides. It follows that the ribityl side chain of factor F0 is derived from the ribose side chain of a nucleotide precursor by reduction. The pyrazine ring of methanopterin is formed by ring expansion involving the ribose side chain of the precursor, GTP.Abbreviations Factor F0
8-hydroxy-6,7-didemethyl-5-deazariboflavin
- APRT
adenine phosphoribosyltransferase
- GPRT
guanine phosphoribosyltransferase
- PRPP
phosphoribosylpyrophosphate
- HPLC
high performance liquid chromatography 相似文献