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1.
Abstract. Anopheles stephensi mosquitoes which had fed upon mice infected with Plasmodium yoelii nigeriensis malaria parasites produced significantly fewer eggs than mosquitoes fed on an uninfected mouse. Fecundity reduction was more pronounced when the bloodmeal contained malaria gametocytes and the mosquitoes developed oocysts. Egg production and haematin excretion were correlated for uninfected bloodfed mosquitoes; the presence of P.y. nigeriensis in the blood affected this relationship. Reduced fecundity was associated with a significant reduction of bloodmeal size (measured by haematin excretion) in mosquitoes which ingested gametocytaemic blood. The bloodmeal size in mosquitoes fed on parasitaemic blood without gametocytes was not significantly reduced. The use of haematin assays for determination of bloodmeal size in mosquitoes is discussed. 相似文献
2.
M. L. Dini J. O'Donnell S. R. Carpenter M. M. Elser J. J. Elser A. M. Bergquist 《Hydrobiologia》1987,150(2):185-191
The timing and magnitude of diel migration in two daphnid assemblages were determined from a series of vertical profiles of daphnid size distribution. Animals were collected concurrently for gut fullness determination. Only large daphnids (> 1.4 mm) migrated, but these animals could account for substantial vertical and diel differences in phosphorus excretion rate. Gut fullness measurements and time courses of diel vertical migration suggested that large Daphnia can cause a net downward flux of phosphorus during summer in thermally stratified lakes. 相似文献
3.
Diurnal variation in ion content of the solution bathing roots of two plants growing together in sand culture was analysed
for three pairs of grass-legume species (Lolium multiflorum andTrifolium pratense; Zea mays andGlycine hispida; Avena sativa andVicia sativa) and their monospecific controls. Biomass and nitrogen content of plants were determined.
Ion concentration (NO
3
−
, NO
2
−
, NH
4
+
, and K+) and pH of root solutions were measured for Lolium-Trifolium plant pairs and controls at 6 hours intervals over 36 h, starting
at 8 am within a circadian cycle. Root solutions were regularly depleted in NO
3
−
by the grasses (Lolium-Lolium control) throughout the cycle. For associations involving the legume (Lolium-Trifolium and
Trifolium-Trifolium), NO
3
−
depletion was followed by NO
3
−
enrichment at night, from late afternoon to early morning; the enrichment was more marked for the Lolium-Trifolium association.
Solutions which did not contain NO
2
−
ions, were enriched by trace amounts of NH
4
+
ions, largely depleted in K+ and alkalanized for all associations throughout the cycle.
Repeating the experiment with the three pairs of species at the vegetative phase of development confirmed the previous results:
NO
3
−
enrichment during the night for associations with legumes. When the experiment was repeated with older plants which had almost
completed their flowering stage, depletion only was observed and no NO
3
−
enrichment.
These data suggest that NO
3
−
enrichment results from N excretion from active nodulated roots of the legume, accounting for the increase in both biomass
and nitrogen content of the companion grass in grass-legume association. The quantitative importance and periodicity of nitrogen
excretion as well as the origin of nitrate enrichment are discussed. 相似文献
4.
Chlorella sorokiniana strain 211-40c, a symbiotic Chlorella isolated from a freshwater sponge, excreted between 3% and 5% of assimilated 14CO2 as glucose in the light, with a pH optimum around 5. This percentage increased when the illuminance was lowered (to 15% at 20 lx). Release of [14C]glucose continued in the dark and could be inhibited by the uncoupler carbonyl cyanide p-trifluoromethoxyphenylhydrazone (FCCP). Net efflux of glucose occurred even at a concentration ratio of extracellular/intracellular glucose of 4. This, together with the sensitivity to FCCP, is taken as evidence for active transport. Exogenous [14C]glucose was taken up by the cells under conditions of net glucose efflux, showing uptake and excretion to take place simultaneously.Abbreviations FCCP
carbonyl cyanide p-trifluoromethoxyphenylhydrazone
- p.c.
packed cells 相似文献
5.
Valérie Toulon Hervé Sentenac Jean-Baptiste Thibaud André Soler David Clarkson Claude Grignon 《Planta》1989,179(2):235-241
The effect of HCO
3
-
on ion absorption by young corn roots was studied in conditions allowing the independent control of both the pH of uptake solution and the CO2 partial pressure in air bubbled through the solution. The surface pH shift in the vicinity of the outer surface of the plasmalemma induced by active H+ excretion was estimated using the initial uptake rate of acetic acid as a pH probe (Sentenac and Grignon (1987) Plant Physiol. 84, 1367). Acetic acid and orthophosphate uptake rates and NO
3
-
accumulation were slowed down, while 86Rb+ uptake and K+ accumulation rates were increased by HCO
3
-
. These effects were similar to those induced by 4-(2-hydroxyethyl)-1-piperazineethane sulfonic acid/2-amino-2-(hydroxymethyl)-1,3-propanediol (Hepes-Tris). They were more pronounced when the H+ excretion was strong, were rapidly reversible and were not additive to those of Hepes-Tris. The hypothesis is advanced that the buffering system CO2/H2CO3/HCO
3
-
accelerated the diffusion of equivalent H+ inside the cell wall towards the medium. This attenuated the surface pH shift in the vicinity the plasma membrane and affected the coupling between the proton pump and cotransport systems.Abbreviations FW
fresh weight
- Hepes
4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid
- Jaa
acetic acid influx
- JK
+
K+ influx
- JPi
orthophosphate influx
- Mes
2-(N-morpholino)ethanesulfonic acid
- pCO2
CO2 partial pressure
- Tris
2-amino-2-(hydroxymethyl)-1,3-propanediol 相似文献
6.
7.
Steve F. Perry Serge Thomas 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1991,161(5):489-497
Summary An extracorporeal circulation of rainbow trout (Oncorhynchus mykiss) was utilized to continuously monitor the rapid and progressive effects of endogenous or exogenous catecholamines on blood respiratory/acid-base status, and to provide in vivo evidence for adrenergic retention of carbon dioxide (CO2) in fish blood (cf. Wood and Perry 1985). Exposure of fish to severe aquatic hypoxia (final P
wO2=40–60 torr; reached within 10–20 min) elicited an initial respiratory alkalosis resulting from hypoxia-induced hyperventilation. However, at a critical arterial oxygen tension (P
aO2) between 15 and 25 torr, fish became agitated for approximately 5 s and a marked (0.2–0.4 pH unit) but transient arterial blood acidosis ensued. This response is characteristic of abrupt catecholamine mobilization into the circulation and subsequent adrenergic activation of red blood cell (RBC) Na+/H+ exchange (Fievet et al. 1987). Within approximately 1–2 min after the activation of RBC Na+/H+ exchange by endogenous catecholamines, there was a significant rise in arterial PCO2 (P
aCO2) whereas arterial PO2 was unaltered; the elevation of P
aCO2 could not be explained by changes in gill ventilation. Pre-treatment of fish with the -adrenoceptor antagonist phentolamine did not prevent the apparent catecholamine-mediated increase of P
aCO2. Conversely, pre-treatment with the -adrenoceptor antagonist sotalol abolished both the activation of the RBC Na+/H+ antiporter and the associated rise in P
aCO2, suggesting a causal relationship between the stimulation of RBC Na+/H+ exchange and the elevation of P
aCO2. To more clearly establish that elevation of plasma catecholamine levels during severe hypoxia was indeed responsible for causing the elevation of P
aCO2, fish were exposed to moderate hypoxia (final P
wO2=60–80 torr) and then injected intraarterially with a bolus of adrenaline to elicit an estimated circulating level of 400 nmol·l-1 immediately after the injection. This protocol activated RBC Na+/H+ exchange as indicated by abrupt changes in arterial pH (pHa). In all fish examined, P
aCO2 increased after injection of exogenous adrenaline. The effects on P
aO2 were inconsistent, although a reduction in this variable was the most frequent response. Gill ventilation frequency and amplitude were unaffected by exogenous adrenaline. Therefore, it is unlikely that ventilatory changes contributed to the consistently observed rise in P
aCO2. Pretreatment of fish with sotalol did not alter the ventilatory response to adrenaline injection but did prevent the stimulation of RBC Na+/H+ exchange and the accompanying increases and decreases in P
aCO2 and P
aO2, respectively. These results suggest that adrenergic elevation of P
aCO2, in addition to the frequently observed reduction of P
aO2 are linked to activation of RBC Na+/H+ exchange. The physiological significance and the potential mechanisms underlying the changes in blood respiratory status after addition of endogenous or exogenous catecholamines to the circulation of hypoxic rainbow trout are discussed.Abbreviations
P
aCO2
arterial carbon dioxide tension
-
P
aO2
arterial oxygen tension
-
P
da
dorsal aortic pressure
-
pHa
arterial pH
-
P
wO2
water oxygen tension
-
RBC
red blood cell
-
V
f
breathing frequency 相似文献
8.
Two strains of Drosophila melanogaster represent the extremes in resistance and sensitivity to the lethal effects of CdCl2. The strain containing the mutations vermilion and brown (v; bw) and the strain Austin had LC50's of 3.3 and 1.3mm CdCl2, respectively. The three major chromosomes from these two strains were assorted genetically into the six possible combinations. The measured LC50's for CdCl2 for these six genotypes fell into two groups according to the X chromosome; those containing the X chromosome from v; bw had LC50's 0.5–1.0mm greater than those in which the X chromosome was from Austin. Since the parent strains differed by 2mm, we suggest that the X chromosome is a major, but not the sole, site of genes to produce resistance to CdCl2. When 109Cd was in the diet the uptake by v; bw and Austin over 2 days was the same. After 4 days of uptake, the Austin strain excreted the 109Cd five times faster than v; bw but the six genotypes did not differ appreciably in excretion rate from one another and resembled the sensitive parent Austin more than the resistant one. Thus a second process is indicated that distinguishes resistance to CdCl2 that apparently is not associated with the X chromosome.This research was sponsored by the Office of Health and Environmental Research, U.S. Department of Energy, under Contract DE-AC05-84OR21400 with Martin Marietta Energy Systems, Inc. 相似文献
9.
A conventional balance study with 48 male weanling rats was conducted to determine true absorption and endogenous fecal excretion
of manganese (Mn) in relation to dietary Mn supply, following the procedures of a previously adapted isotope dilution technique.
After 10 d on a diet with 1.5 ppm Mn, eight animals each were assigned to diets containing 1.5, 4.5, 11.2, 35, 65, or 100
ppm Mn on a dry-matter basis. Three days later, each rat was given an intramuscular54Mn injection and kept on treatment for a balance period of 16 d.
Apparent Mn absorption assessed for the final 8 d, averaged 8.6 μg/d without significant treatment effects, although Mn intake
ranged from 18.6 to 1200 μg/d, in direct relation to dietary Mn concentrations. Mean fecal excretion of endogenous Mn for
the six treatments was 0.9, 2.7, 7.4, 11.0, 16.3, and 17.7 μg/d, respectively. These values delineate the rates to which true
absorption exceeded apparent rates. True absorption, as percent of Mn intake, averaged 28.7, 15.9, 11.7, 6.1, 3.4, and 2.0,
respectively, as compared with mean values of 23.9, 10.9, 6.2, 3.4, 1.2, and 0.5 for percent apparent absorption. It was concluded
that both true absorption and endogenous fecal excretion markedly responded to Mn nutrition and that the reduction in the
efficiency of true absorption was quantitatively the most significant homeostatic response for maintaining stable Mn concentrations
in body tissues. 相似文献
10.
The influence of dietary supplementation with thiamine on lead (Pb) contents in blood and tissues, blood δ-aminolevulinic
acid dehydratase (δ-ALAD) activity, and urinary excretion of δ-aminolevulinic acid (δ-ALA) was evaluated in male Sprague-Dawley
rats. Groups of randomly selected animals were given a thiamine-deficient diet, a diet containing normal thiamine (20 mg/kg),
or a thiamine-supplemented diet (50 mg/kg), along with control drinking water or water containing 100 ppm Pb, for 4 mo. Animals
fed the thiamine-supplemented diet (50 mg/kg) and Pb showed decreased urinary excretion of δ-ALA and a decreased inhibition
of δ-ALAD activity in blood compared to those given Pb with normal thiamine diet. The liver, kidney, and blood of rats receiving
supplemental thiamine also contained significantly less Pb than the other two treatment groups given Pb-containing water.
The protective effect of thiamine against Pb toxicity may be attributed to its interference with retention of the metal in
body tissue, possibly resulting from the formation of excretable thiamine-lead complexes. 相似文献