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231.
Elisabeth Balstad Magnussen Lars Johan Vatten Tom Ivar Lund-Nilsen Kjell ?smund Salvesen George Davey Smith P?l Richard Romundstad 《BMJ (Clinical research ed.)》2007,335(7627):978
Objective To examine the effect of cardiovascular risk factors before pregnancy on risk of pre-eclampsia.Design Population based prospective study.Setting Linkage between a Norwegian population based study (Nord-Trøndelag health study, HUNT-2) and Norway''s medical birth registry.Participants 3494 women who gave birth after participating in the Nord-Trøndelag health study at baseline; of whom 133 (3.8%) delivered after a pre-eclamptic pregnancy.Main outcome measure Odds ratio of developing pre-eclampsia.Results After adjustment for smoking; previous pre-eclampsia; parity; maternal age, education, and socioeconomic position; and duration between baseline measurements and delivery, positive associations were found between prepregnancy serum levels of triglycerides, cholesterol, low density lipoprotein cholesterol, non-high density lipoprotein cholesterol, and blood pressure and risk of pre-eclampsia. The odds ratio of developing pre-eclampsia for women with baseline systolic blood pressures greater than 130 mm Hg (highest fifth) was 7.3 (95% confidence interval 3.1 to 17.2) compared with women with systolic blood pressures less than 111 mm Hg (lowest fifth). Similar results were found for nulliparous and parous women. Women who used oral contraceptives at baseline had half the risk of pre-eclampsia compared with never or former users (0.5, 0.3 to 0.9).Conclusion Women with cardiovascular risk factors may be predisposed to pre-eclampsia. 相似文献
232.
What regulate and limit reindeer populations in Norway? 总被引:5,自引:0,他引:5
Torkild Tveraa Per Fauchald Nigel Gilles Yoccoz Rolf Anker Ims Ronny Aanes Kjell Arild Høgda 《Oikos》2007,116(4):706-715
An understanding of how species are affected by top-down and bottom-up processes in food webs, and how these forces interact with climatic conditions is crucial for how ecosystems should be managed. In Norway large carnivores are effectively removed from extensive areas to protect livestock, leaving human harvesting as the only significant top-down force on ungulate populations. We examined the relative role of top-down and bottom-up processes for 58 semi-domesticated reindeer populations in Norway subjected to contrasting climatic regimes over the period 1981–2005. Intensive herding and international agreement have resulted in a situation where some populations are unable to undertake seasonal migration to the interior to escape the unfavourable climatic conditions that rule the coastal region in the winter, a critical season for northern ungulates. We used this natural manipulation to contrast between populations with 'poor' and 'good' winter conditions. For populations with good winter conditions, average body size increased with harvesting, suggesting that some top-down process was necessary to avoid food limitation. Time-series analyses revealed that direct regulation of population size was only evident in populations subjected to intensive harvesting. The lack of direct regulation in populations subjected to low harvesting resulted in high vulnerability to harsh winter weather. The body size and climate vulnerability of populations with poor winter conditions was unaffected of harvesting, but average densities was positively related to overall vegetation productivity as indexed by satellite images (NDVI). Top-down processes appeared to be necessary to dampen the effect of harsh winters in populations with generally good winter conditions. Conversely, populations subjected to generally poor winter conditions appeared to be more influenced by bottom-up processes and buffered climatic perturbations by increasing body size. 相似文献
233.
Migrating Arctic charr (Salvelinus alpinus) parr (118 ± 34.4 mm) were caught close to the rivermouth of the Dieset river on Spitsbergen (79°10′N), Svalbard. When subjected
to a seawater tolerance test (34 ppt at 6°C) their blood plasma osmolality and sodium and magnesium concentrations increased
significantly. After 90 h of exposure, average plasma osmolality was 410 (±54.1) mOsmol. Corresponding sodium and magnesium
concentrations were 207 (±35.9) mmol l−1 and 2.7 (±1.36) mmol l−1, respectively. Survival at this time was only 12.5%. When smaller fish (96 ± 26.6 mm) were exposed to seawater, mortality
was 100% within 72 h. We conclude that small-sized Svalbard charr may survive only short periods in seawater. Therefore, the
lack of adequate hypoosmoregulatory capacity limits their access to marine food resources.
Received: 29 December 1997 / Accepted: 12 April 1998 相似文献
234.
Nearly all vertebrate cells have been shown to express heparan sulfate proteoglycans
(HSPGs) at the cell surface. The HSPGs bind to many secreted signaling proteins, including
numerous growth factors, cytokines, and morphogens, to affect their tissue distribution
and signaling. The heparan sulfate (HS) chains may have variable length and may differ
with regard to both degree and pattern of sulfation. As the sulfation pattern of HS chains
in most cases will determine if an interaction with a potential ligand will take place, as
well as the affinity of the interaction, a key to understanding the function of HSPGs is
to clarify how HS biosynthesis is regulated in different biological contexts. This review
provides an introduction to the current understanding of HS biosynthesis and its
regulation, and identifies research areas where more knowledge is needed to better
understand how the HS biosynthetic machinery works. 相似文献
235.
Jens Peter Lomholt Kjell Johansen 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1976,107(2):141-157
1. | Gas exchange and blood gas transport has been studied in the amphibious teleost,Amphipnous cuchia. A. cuchia is a bimodal breather. Respiratory gas exchange takes place in a pair of specialized air sacs extending from the pharyngeal cavity. Aquatic and aerial gas exchange also takes place in vestigial gills, across buccopharyngeal surfaces and in the skin. All blood draining the air sacs is returned via systemic veins to the heart before systemic distribution. |
2. | Oxygen uptake in fish kept in water with access to air was 33.3±8.0 ml O2STP·kg–1·h–1. About 65% of this uptake resulted from air breathing. Upon removal from water the O2 uptake rose to 44.6±15.7 ml O2· kg–1·h–1, while confinement to water breathing reduced the O2 uptake to 16.4±2.7 ml O2·kg–1·h–1. The latter value was 50% higher than aquatic O2 uptake when air breathing was available. |
3. | Amphipnous practices periodic breathing and normal breathhold periods last 8–10 min. In the early phase of breathholding the gas exchange ratio (RE) was close to 0.7 but declined to low levels with breathholding. Mean RE for an average breathhold was 0.2. The low RE of the air sacs results from a high cutaneous CO2 elimination in water as well as in moist air. Estimated blood flows to the air sacs indicate flow of about 20 ml min–1 shortly after an air breath declining to 5 ml·min–1 late in a breath-hold period. |
4. | Due to the shunting of air sac blood to systemic venous (jugular vein) blood, the jugular vein P\textO2 P_{{\text{O}}_2 } carried the most oxygenated blood averaging 35.2 mm Hg, the dorsal aorta 23.4 mm Hg and the hepatic vein 18.6 mm Hg. |
5. | A. cuchia blood has a very high Hb concentration and O2 capacity reaching 15.5 gram % and 22 vol%, respectively. TheP 50 value was 7.9 mm Hg at pH 7.6. The Bohr factor, was –0.57, then-value 2.05 and the temperature sensitivity of the O2-Hb binding expressed by H=–13.1 Kcal·mole Hb–1. Buffering capacity was high: 34.1 mM HCO3 –·1–1. |
6. | The vascular configuration inA. cuchia suggests a low efficiency of gas transport. A high blood O2 capacity and O2 affinity and a high cardiac output reduce the efficiency loss and permit the fish to suspend with air breathing for up to 30 min with a modest reduction in arterial O2 saturation from near 90% to 60%. The high blood O2 affinity allows breathholding to occur at reduced rates of systemic blood flow due to the large O2 stores available in venous blood during normal breathing. |
7. | Ventral aortic blood pressure fell from about 60 mm Hg systolic value to 40 mm Hg in the dorsal aorta indicating considerable vascular resistance in the shunt connecting these vessels. The pressure gradient across the shunt remained unchanged with the breathhold cycle and is thus not part of the vasomotor activity controlling blood flow to the aerial gas exchanger. |
8. | The data are discussed in relation to other air breathing fishes, notably the electric eel,Electrophorus electricus, and the African lungfish,Protopterus aethiopicus. |
236.
Hanssen SA Hasselquist D Folstad I Erikstad KE 《Proceedings. Biological sciences / The Royal Society》2005,272(1567):1039-1046
Life-history theory predicts that increased current reproductive effort should lead to a fitness cost. This cost of reproduction may be observed as reduced survival or future reproduction, and may be caused by temporal suppression of immune function in stressed or hard-working individuals. In birds, consideration of the costs of incubating eggs has largely been neglected in favour of the costs of brood rearing. We manipulated incubation demand in two breeding seasons (2000 and 2001) in female common eiders (Somateria mollissima) by creating clutches of three and six eggs (natural range 3-6 eggs). The common eider is a long-lived sea-duck where females do not eat during the incubation period. Mass loss increased and immune function (lymphocyte levels and specific antibody response to the non-pathogenic antigens diphtheria and tetanus toxoid) was reduced in females incubating large clutches. The increased incubation effort among females assigned to large incubation demand did not lead to adverse effects on current reproduction or return rate in the next breeding season. However, large incubation demand resulted in long-term fitness costs through reduced fecundity the year after manipulation. Our data show that in eiders, a long-lived species, the cost of high incubation demand is paid in the currency of reduced future fecundity, possibly mediated by reduced immune function. 相似文献
237.
238.
Robert E. Chapin Timothy Winton William Nowland Nichole Danis Steven Kumpf Kjell Johnson Aleasha Coburn Jan‐Bernd Stukenborg 《Birth defects research. Part B, Developmental and reproductive toxicology》2016,107(6):225-242
The last two decades have seen an increasing search for in vitro models that can replace the use of animals for safety testing. We adapted the methods from a recent nonquantitative report of spermatogenesis occurring in ex vivo mouse testis explants and tried to develop them into a screening assay. The model consisted of small pieces of neonatal mouse testis (testis “chunks”), explanted and placed on pillars of agarose or chamber inserts, and cultured at the air–liquid interface. A peripheral torus‐shaped zone in these explants would often contain tubules showing spermatogenesis, while the middle of each chunk was often necrotic, depending on the thickness of the tissue. The endpoint was histology: what proportion of tubules in the “permissive torus” actually contained healthy pachytene spermatocytes or spermatids? Extensive statistical modeling revealed that a useful predictive model required more than 60% of these tubules to show spermatogenesis. Separately, the logistics of running this as a predictive assay require that the controls consistently produce ≥ 60% tubules with pachytenes and round spermatids, and achieving this level of spermatogenesis reliably and consistently every week proved ultimately not possible. Extensive trials with various media additions and amendments proved incapable of maintaining the frequency of spermatogenic tubules at consistently ≥ 60%. Congruent with Schooler's “decline effect”; generally, the more often we ran these cultures, the worse the performance became. We hope that future efforts in this area may use our experience as a starting point on the way to a fully productive in vitro model of spermatogenesis. 相似文献
239.
240.
Epidemiological studies related to radiofrequency (RF) electromagnetic fields (EMF) have mainly used crude proxies for exposure, such as job titles, distance to, or use of different equipment emitting RF EMF. The Royal Norwegian Navy (RNoN) has measured RF field emitted from high‐frequency antennas and radars on several spots where the crew would most likely be located aboard fast patrol boats (FPB). These boats are small, with short distance between the crew and the equipment emitting RF field. We have described the measured RF exposure aboard FPB and suggested different methods for calculations of total exposure and annual dose. Linear and spatial average in addition to percentage of ICNIRP and squared deviation of ICNIRP has been used. The methods will form the basis of a job exposure matrix where relative differences in exposure between groups of crew members can be used in further epidemiological studies of reproductive health. Bioelectromagnetics 31:350–360, 2010. © 2010 Wiley‐Liss, Inc. 相似文献