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11.
Sue Piper Duckles 《Neurobiology of aging》1983,4(2):151-156
The adrenergic control of vascular smooth muscle was compared in young and adult rabbits using a variety of in vitro techniques. Norepinephrine (NE) content and accumulation of 3H-NE were not different in blood vessels from the two age groups. In contrast, stimulation-evoked release of endogenous NE was reduced by 40–60% in vessels from the aged animals. Functional studies of smooth muscle contractions were carried out using isolated ring segments of the ear artery. There were no differences in the resting force-response relationship between vessels from young and adult rabbits. Maximum contractile responses to nerve stimulation, NE or KCl were not different in vessels from the two age groups, nor was the NE ED50. However, blockade of the neuronal uptake system with desmethylimipramine produced a greater shift in the NE concentration-response curve in vessels from the young animals compared to the shift in vessels from adult animals. This observation reflects a decline in neuronal NE uptake with age. Although maximal contractile responses to transmural nerve stimulation at 16 Hz were unchanged, responses to stimulation at lower frequencies were reduced in vessels from adult rabbits, an effect which was also enhanced when an antagonist of neuronal uptake was present. Thus, there is a decline in function of adrenergic nerves in adult animals, reflected in a decrease in stimulation-evoked NE release and a decrease in norepinephrine uptake revealed by functional studies. These two effects tend to balance each other, so that there is a small decrease in contractile response to adrenergic nerve stimulation which is exacerbated when neuronal uptake mechanisms are blocked. 相似文献
12.
Why there are so few gametocytes (the transmission stage of malaria) in the blood of humans infected with Plasmodium spp. is intriguing. This may be due either to reproductive restraint by the parasite or to unidentified gametocyte-specific immune-mediated clearance mechanisms. We propose another mechanism, a cross-stage immunity to Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP-1). This molecule is expressed on the surface of the erythrocyte infected with either trophozoite or early gametocyte parasites. Immunoglobulin G antibodies to PfEMP-1, expressed on both life cycle stages, were measured in residents from an area where malaria is endemic, Papua New Guinea. Anti-PfEMP-1 prevalence increased with age, mirroring the decline in both the prevalence and the density of asexual and transmission stages in erythrocytes. These data led us to propose that immunity to PfEMP-1 may influence malaria transmission by regulation of the production of gametocytes. This regulation may be achieved in two ways: (i) by controlling asexual proliferation and density and (ii) by affecting gametocyte maturation. 相似文献
13.
H. M. Piper 《Journal of molecular medicine (Berlin, Germany)》1989,67(9):465-476
Summary After prolonged ischemia or hypoxia myocardial injury is not reversed but exacerbated by a resupply of the tissue with oxygen and substrates. The mechanism by which reversible ischemic or hypoxic myocardial injury becomes irreversible is not yet understood. It has been debated whether reperfusion injury merely uncovers pre-existing irreversible injury, or is indeed caused by the reperfusion/reoxygenation process. In recent years, three theories have been discussed that relate the onset of irreversibility either to: a critical energy loss; a critical accumulation of cellular calcium; or to the deleterious effects of free radical formation. In certain experimental models for each of these theories favourable results have been obtained. Current research suggests that absolute reversibility thresholds in energy depletion or calcium accumulation in the ischemic or hypoxic cell do not exist. A key role of free radical injury for reperfusion injury must also be questioned. There is, however, evidence that in tissue reversibility of ischemic cardiomyocyte injury is limited by conditions that make calcium-induced hypercontracture upon reoxygenation unavoidable. This occurs when, by hypercontracture, mutual mechanical disruption of the cells destroys the tissue. From isolated cardiomyocytes that are able to metabolically survive hypercontracture it has been observed that these metabolic conditions do not represent the last biological possibility to reverse injury. 相似文献
14.
D. Pelzer G. Trube H. M. Piper 《Pflügers Archiv : European journal of physiology》1984,400(2):197-199
Single myocytes from adult rat hearts were prepared following the method of Powell and co-workers (9, 10, 11). Low resting potentials (Em) could be improved by three techniques. (i) Elevation of Cao to 7.2 mM which, however, mostly resulted in spontaneity and irreversible contracture. (ii) Pre-incubation in a KB medium (6). (iii) Use of suction pipettes instead of tapered microelectrodes for intracellular recordings (2). It is concluded that low Em measured previously (11) were due to membrane damage upon microelectrode impalement accopanied by insfufficient healing of the membrane around the electrode insertion. 相似文献
15.
Keith S. Hansen Hila Ghersin Merisa Piper Mehdi Tavakol Brian Lee Laura J. Esserman John P. Roberts Chris Freise Nancy L. Ascher Rita A. Mukhtar 《American journal of transplantation》2021,21(9):3014-3020
Kidney transplantation reduces mortality in patients with end stage renal disease (ESRD). Decisions about performing kidney transplantation in the setting of a prior cancer are challenging, as cancer recurrence in the setting of immunosuppression can result in poor outcomes. For cancer of the breast, rapid advances in molecular characterization have allowed improved prognostication, which is not reflected in current guidelines. We developed a 19-question survey to determine transplant surgeons’ knowledge, practice, and attitudes regarding guidelines for kidney transplantation in women with breast cancer. Of the 129 respondents from 32 states and 14 countries, 74.8% felt that current guidelines are inadequate. Surgeons outside the United States (US) were more likely to consider transplantation in a breast cancer patient without a waiting period (p = .017). Within the US, 29.2% of surgeons in the Western region would consider transplantation without a waiting period, versus 3.6% of surgeons in the East (p = .004). Encouragingly, 90.4% of providers surveyed would consider eliminating wait-times for women with a low risk of cancer recurrence based on the accurate prediction of molecular assays. These findings support the need for new guidelines incorporating individualized recurrence risk to improve care of ESRD patients with breast cancer. 相似文献
16.
Ultrastructure of cultured adult myocardial cells during anoxia and reoxygenation. 总被引:3,自引:2,他引:3 下载免费PDF全文
P. Schwartz H. M. Piper R. Spahr P. G. Spieckermann 《The American journal of pathology》1984,115(3):349-361
Cultured heart cells from adult rats were exposed to anoxia in a substrate-free Tyrode's solution at constant pH. In this system the metabolic and the morphologic pattern can be investigated simultaneously. Anoxic changes develop gradually above 2 mumol adenosine triphosphate (ATP)/ gww . Morphometry reveals that the morphologic changes are closely related to the energetic state: creatine phosphate (CP) decay is accompanied by the loss of small mitochondrial matrix granules (r = 0.97). The fall of ATP is coincident with sarcomere shortening (r = 0.95) and, below 4 mumol/ gww , with mitochondrial swelling (r = -0.88). The number of lipid droplets correlates with the ATP level during anoxia and reoxygenation (r = -0.92). The early energetic depletion is accompanied by a moderate release of cytosolic enzymes and morphologic changes: the appearance of sarcolemmal microblebs and an increase in subsarcolemmal vesicles. Below an average ATP level of 2 mumol/ gww an increasing number of individual cells fail to recover when reoxygenated . However, that failure is accompanied neither by massive enzyme release nor by ultrastructural damage regarded as typical for the "oxygen paradox." 相似文献
17.
Bone resorption may be stimulated by increased parathyroid hormone secretion, certain cytokines, and other bone-resorbing mediators. Low serum calcium levels promote parathyroid hormone secretion, and estrogen deficiency is associated with a rise in cytokine production and activity. An abnormal proliferation of mast cells may also release cytokines, heparin, and other mediators of bone resorption. 相似文献
18.
In ischemic-reperfused myocardium, necrosis of cardiomyocytes may develop not only due to the ischemic conditions but also the specific circumstances of reperfusion. The existence of reperfusion injury becomes apparent when modifications of the conditions of reperfusion can prevent cell death otherwise occurring. Three prime causes of rapidly developing reperfusion injury are here discussed, ie, reenergization of cells at increased cytosolic Ca2+ contents, rapid normalization of tissue pH, and rapid normalization of tissue osmolality. All three causes lead to severe mechanical stress of cardiomyocytes which can cause their rapid deterioration. Propagation of cell injury among adjacent cells can cause a spreading of necrosis throughout myocardial tissue. The understanding of these initial causes of rapidly developing lethal reperfusion injury leads to new concepts for specific protection of reperfused myocardium. 相似文献
19.
The presence of therapy manuals in clinical settings is increasing and the related concepts of adherence and competence are becoming familiar. The benefits of manuals for research and training are evident. However, negative clinical effects have also been reported. Dynamically oriented clinicians and researchers who use manuals face a dilemma. Although there is a need to control aspects of technique for research and training purposes, there is also a need not to control the process of therapy because unpredictability is an intended part of the process. Issues associated with the dilemma are reviewed and a possible solution is provided that has proven helpful in an active clinic and research setting. It involves the use of manuals that emphasize general guidelines rather than detailed technical behaviors. 相似文献
20.
H F Piper 《Klinische Monatsbl?tter für Augenheilkunde》1999,215(2):73-77
In 1858 Panum published a monography on "Physiologische Untersuchungen über das Sehen mit zwei Augen". He proposed the concept of corresponding circles of perception instead of the absolute identity of corresponding points on the retina. This was met with opposition particularly by A. W. Volkmann of Halle who tried to explain psychologically all stereoscopic phenomena (Arch. Ophthalmol., 1859). Both authors defended their views with numerous experiments. Panum's results in "Uber einheitliche Verschmelzung verschiedenartiger Netzhauteindrücke beim Sehen mit zwei Augen" (Arch. Anatomie, 1861) is still valid today. 相似文献