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PubMed2002

The control of the proventriculus in the honeybee (Apis mellifera carnica L.) I. A dynamic process influenced by food quality and quantity?

The control of crop emptying in foraging honeybees was investigated in individuals trained to collect defined amounts of sugar solutions. Following feeding, they were dissected after fixed periods of time in order to measure crop content and haemolymph sugar titers. Between feeding and dissection, the metabolic rate of every investigated forager was measured using open-flow respirometry, so as to assess the effects of both food quality (concentration, molarity and viscosity of the fed sugar solution) and food quantity on the transport rate through the proventriculus. The sugar transport rate through the proventriculus was observed to be mainly dependent on the metabolic expenditure of the individual. Bee foragers were able to precisely adjust the sugar transport rate to their metabolic rates, but under certain conditions, an excess of sugars was transported through the proventriculus, more than needed to cover the bee's energetic demands. This excess depended on the nutritive value and quantity of the fed sugar solution, and on the time after feeding. It did not depend on the metabolic rate of the bee, the molarity, or the viscosity of the fed sugar solution. As long as the bees did not exhaust their crop contents, the haemolymph sugar titers were unaffected by this excess amount transported, by the time after feeding, the concentration and the viscosity of the fed sugar solution. For all feeding conditions assayed, the haemolymph trehalose titer remained constant, while the titers of other haemolymph sugars varied. It is suggested that the trehalose concentration in the haemolymph is regulated in honeybees, and that it represents the controlled variable in the feedback loop responsible for the transport rate through the proventriculus.

Journal Article↗
PubMed1988

Intermittent coronary sinus occlusion in humans: pressure dynamics and calculation of diagnostic quantities.

Pressure controlled intermittent coronary sinus occlusion (PISCO) was applied in 30 patients undergoing coronary artery bypass surgery. The occlusion and release times were manually adjusted according to visual control of the intraoperatively monitored coronary sinus pressure. In six patients the coronary sinus measurements were additionally digitised with a personal computer before postoperative mathematical analysis, which comprised automatic detection of systolic peaks, diastolic troughs, and the calculation of derived quantities. The purpose of the analysis was (a) to assess quantitatively human coronary sinus pressure dynamics, (b) to determine whether visual control and interpretation of coronary sinus pressure rise could be replaced by a mathematical model, and (c) to ascertain whether the occlusion and release cycle lengths were adequate. Numerical estimates for intraindividual and interindividual spread of calculated quantities were produced, the mathematically obtained results were related to a possible physiological interpretation, and the most efficient method of statistical analysis was ascertained. These results form the numerical basis for a closed loop adjustment of pressure controlled intermittent coronary sinus occlusion cycling.

Aged↗
PubMed1989

[The relations between doses of streptozotocin and pathosis in induced diabetes mellitus].

Tail-vein injections of streptozotocin (STZ) in various doses (20-60 mg/kg body weight) were used to induce diabetes mellitus in male rats of the Sprague-Dawley strain. Resulting pathosis was observed on the basis of various parameters (body weight, blood glucose, plasma insulin, glucose-tolerance tests, uroscopy, hemodiagnosis, and skin strength) Results 1. Diabetes mellitus was induced in all rats of the group in which the dosage was STZ 40 mg/kg body weight (S-40 group). Blood-glucose level in this group was about 340 mg (3 times the quantity in controls). Plasma-insulin level was about 8.9 microU/ml (about 1/3 the quantity in controls). Glucose-tolerance tests and observation of urino-glucose showed reductions in glucose tolerance and plasma-insulin response. 2. In the S-40 group, pathosis of induced diabetes mellitus had stabilized 30 days after and persisted for 90 days after STZ injection. 3. Skin strength decreased for 20 days after STZ injection. The level remained stable at half the strength of control skin from 30 to 90 days after the injection. 4. In groups in which doses were STZ 20 mg/kg body weight or STZ 30 mg/kg body weight, diabetes mellitus was induced in some of the rats. The animals tended to recover from the induced pathosis. 5. Diabetes mellitus was induced in all rats to which doses of STZ 50 mg/kg or STZ60 mg/kg body weight were induced. shortly after injection, the induced-diabetes pathosis changed for the worse; and grave complications (hypo-albuminosis, diabetic ketocacidosis, and diabetic proteinuria) were observed. A large number of the rats in these groups died. 6. The results of this study confirm the opinion that STZ 40 mg/kg body weight is the optimum dose for STZ induction of diabetes mellitus in rats for experimental studies. The suitable term for such studies is from 30 to 90 days after STZ injection.

Animals↗
PubMed2005

Oxygen levels versus chemical pollutants: do they have similar influence on macrofaunal assemblages? A case study in a harbour with two opposing entrances.

Generally, harbours are polluted zones characterised by low values of hydrodynamism and oxygen in the water column and high concentrations of pollutants in sediments. The harbour of Ceuta, North Africa, has an unusual structure; it is located between two bays connected by a channel, which increases the water movement and exchange in the harbour, maintaining moderate oxygen levels in the water-sediment interface. Nevertheless, high concentration of organic matter, nutrients and heavy metals were measured in sediments from this harbour. Under these unusual conditions (high levels of pollution but total saturation of oxygen in the water column) we studied the responses of soft-bottom macrobenthic communities using uni and multivariate analyses. The number of species was similar inside and outside the harbour but the species composition differed between internal and external stations; oxygen levels seem to control the "quantity" of species whereas pollutants control the "quality" of them.

Animals↗
PubMed2000

Gender and context differences in alcohol expectancies.

In 2 studies, the authors investigated gender and context effects of alcohol expectancies among U.S. college students. In Study 1, they examined the responses of 771 women and 493 men to the Sexual Enhancement (SE) subscale and the Relaxation and Tension Reduction (TR) subscale of the Alcohol Expectancy Questionnaire (S. A. Brown, B. A. Christiansen, & M. S. Goldman, 1987). They found no gender differences when they controlled for drinking quantity. When they controlled for drinking frequency, the men scored significantly higher on the TR subscale than the women did. In Study 2, also among U.S. college students, 41 women and 21 men first imagined that they were on blind dates or in long-term relationships and then completed the SE and TR subscales. On the SE subscale, the women scored higher in the relationship context than in the blind-date context, whereas the men did not vary between contexts. All the participants also reported more tension-reduction expectancies in the relationship context than in the blind-date context.

Adolescent↗
PubMed1988

Role of absorptive and secretory processes in hydration of the airway surface.

In the conducting airways, epithelial electrolyte transport processes play an important role in controlling the quantity and the composition of the airway surface solution layer. Hydration of the airway surface appears to promote effective mucociliary clearance and to influence the rheology of mucins, and together these factors provide a major mechanism for airway defense. The cellular processes governing absorption and secretion of salt are similar, if not identical, to those that have been described in a variety of other absorptive and secretory epithelial cells where they may be studied in isolation. A better molecular understanding of the channels that control apical membrane transport of Na and Cl, the rate-determining steps in salt absorption and secretion, should enhance our basic understanding of the factors that control the quantity and composition of airway fluids. This may elucidate the mechanisms for the reciprocal control of apical Na and Cl channel activities and provide an explanation for the balance between these oppositely directed salt transport processes.

Absorption↗
PubMed2004

Peculiarities [correction of Pfculiarities] of lipid accumulation in Brassica rapa L. embryos on different stages development under altered gravity.

Accumulation of lipid inclusions in Brassica rapa embryos generated under slow horizontal clinorotation and in the laboratory control were analyzed by histochemical methods. The research of lipid accumulation was carried out on consecutive stages of the embryo development, from the moment of two-cellular proembryo formation up to the stages of their full differentiation (21-22-day-old embryos). Accumulation of lipid drops was revealed for the first time at early stages of embryogenesis in this species, beginning from 3-day-old embryos (ball-like stage of embryo development) under clinorotation and in the laboratory control. The quantity of lipid inclusion was estimated by morphometrical analysis. Statistically significant differences between the clinorotation and laboratory control variants in quantity of lipid drops per cell were revealed from 6-day-old embryos (heart-shaped stage). Especially pronounced differences were noted in differentiated embryos (beginning from 12-day-old embryos) under horizontal clinorotation in comparison with the laboratory control. The registered differences testify about influence of altered gravity conditions on lipid accumulation in Brassica rapa embryos.

Brassica rapa↗
PubMedDate not supplied

An in vivo study of the impact of different emergence profiles of procera titanium crowns on quantity and quality of plaque.

PURPOSE: The purpose of this study was to evaluate the effect of crowns with different emergence profiles on marginal plaque formation. MATERIALS AND METHODS: Seven crown preparations were performed on premolar teeth in six patients. Four titanium crowns for each tooth--with different marginal emergence angles--were manufactured according to the Procera technique. The three experimental crowns and the final permanent tooth were cemented with phosphate permanent cement. Plaque samples were collected from the marginal area after 1 week with normal oral hygiene, and again after refraining from oral hygiene for 2 days. The contralateral tooth served as a control. The quantity and quality of plaque were registered. The restoration was removed, the next crown version cemented, and the protocol repeated. RESULTS: All experimental crowns, irrespective of emergence profile, showed a significantly lower (P = .01) plaque quantity than controls. No intraindividual differences were found regarding the accumulation of mutans streptococci at the different experimental emergence profiles. No differences in quality between experimental and control sides were found. CONCLUSION: Within the limitations of this study, it was found that titanium crowns with emergence profiles of up to 40 degrees formed less plaque than healthy controls. There was no higher accumulation of mutans streptococci in relation to increasing emergence profiles.

Adult↗
PubMed2002

Theory for the optimal control of time-averaged quantities in quantum systems.

We present a variational theory for the optimal control of quantum systems with relaxation over a finite time interval. In our approach, which is a nontrivial generalization of previous formulations and which contains them as limiting cases, the optimal control field fulfills a high-order Euler-Lagrange differential equation, which guarantees the uniqueness of the solution. We solve this equation numerically and also analytically for some limiting cases. The theory is applied to two-level quantum systems with relaxation, for which we determine quantitatively how relaxation effects limit the control of the system.

Journal Article↗
PubMed2000

Xenoesterogens and male infertility: myth or reality?

AIM: To evaluate the role of polychlorinated biphenyls (PCBs) as a potential environmental hazard in the deterioration of male fertility. METHODS: Fifty-three males were studied. After a thorough case history evaluation and relevant clinical and laboratory investigations, PCBs were estimated in the seminal plasma of 21 infertile men with "Unexplained Male Factor" and 32 fertile controls. Peak retention times of the eluants were compared with those of the commercially available standard PCB Mix, and the results confirmed spectrophotometrically. Seminal PCB concentrations were compared between i) fertile and infertile men and ii) men from different areas and diets. The relationship between PCB concentrations and measures of sperm quality such as the total motile sperm count, was assessed. RESULTS: PCBs were detected in seminal plasma of infertile men but absent from controls. Sperm quantity and quality were significantly lower in infertile men compared to controls. The highest average PCB concentrations were found in fish-eating urban dwellers, and followed in succession by fish-eating rural dwellers, non fish-eating urban dwellers and non fish-eating rural dwellers. The total motile sperm counts were inversely proportional to the PCB concentrations and were significantly lower than those of the respective controls. CONCLUSION: PCBs may be instrumental in the deterioration of sperm quantity and quality, a contaminated fish diet being the main source of exposure.

Adult↗
PubMed2003

[Determining the quantity of hypericin in medicinal materials and asepsis seedings of Hypericum perforatum by HPLC].

OBJECTIVE: To establish the method of determining the quantity of hypericin in Hypericum perforatum and determine the quantity of the hypericin in defferent medicinal materials and asepsis seedings which grow in defferent environment. METHOD: The specimen is extracted with methanol--Pyridine (9:1) ultrasound extraction. Chromatographic assay is performed on a hypersily ODS2 (4.6 mm x 150 mm, 5 microm) column. The mobile phase is composed of methanol -1.56% dihydric natrium phosphate hydrogen natrium solution (shift solution's acidity to 2.1 with phosphoric acid)--ethyl acetate (4:1.9:1), velocity of flow is 1 mL x min(-1); column temperature is 35 degrees C; the detection wavelength is 590 nm. RESULT: A satisfactory seperaration between hypericin and impurity. The calibration curve is linear over the range of 0.0524-0.2620 microg for hypericin (r = 0.9998). The average recovery of hypericin is 97.50%. CONCLUSION: The quantity of hypericin in Hypericum perforatum has something to do with the genetic factor, environment factor, growing period and dry means. The method of determining the quantity of hypericin can be regarded as the method of controling the quantity of medicinal materials.

Anthracenes↗
PubMed2003

Surface T-cell antigen receptor expression and availability for long-term antigenic signaling.

It is important to understand how T-cell antigen receptor (TCR) engagement and signaling are regulated throughout an immune response. This review examines the dynamics of surface TCR expression and signaling capacity during thymic and effector T-cell development. Although the TCR can undergo vast changes in surface expression, T cells remain capable of sustaining TCR engagement for long periods of time. This may be achieved by a combination of mechanisms that involve (a) controlling the quantity of surface TCR available for ligand interaction and (b) controlling the quality of surface TCR expression during T-cell activation. TCR signaling itself appears to be one of the main quantitative modulators of surface TCR expression, and it can cause both downregulation and upregulation at different times of T-cell activation. Recent studies indicate that the degree of upregulation is tunable by the strength of antigenic stimulation. There is evidence that qualitatively distinct forms of the TCR exist, and their potential role in sustained antigenic signaling is also discussed. A goal of future studies will be to better characterize these modulations in surface TCR expression and to clarify their impact on the regulation of immune responses.

Animals↗