SEARCH · PubMed Health

Results for “Environment, Controlled”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 703 records · Page 39Linked to original sources

PubMed1981

Prophylactic effects of sodium cromoglycate on chronic obstructive pulmonary disease in the horse.

When stabled in a controlled environment, horses effected with chronic obstructive pulmonary disease (COPD) became clinically asymptomatic in 4 to 32 days (mean [+/-sd] 9.1 +/- 4.9 days), the time being influenced most by the severity of the disease judged on maximum intrathoracic pressure change (Max delta Ppl) and the age of the animal. Sodium cromoglycate, a drug widely used for prophylaxis of allergic respiratory disease in man, was administered by inhalation to 56 COPD-affected horses. The results showed that a linear response existed between the number of successive days treatment with this drug and the duration of remission of clinical signs of COPD while horses were exposed to natural antigen (poor quality straw bedding). Sodium cromoglycate given as a single daily dose (80 mg) on one day and on 4 successive days prevented clinical signs for mean 3.6 days and mean 24.3 days, respectively. These results indicate that prophylactic treatment with inhaled sodium cromoglycate is an effective method of controlling the clinical signs of COPD.

Animals↗

PubMed2000

Experimental models of porcine post-weaning colibacillosis and their relationship to post-weaning diarrhoea and digestive disorders as encountered in the field.

The aim of this study was to develop a reliable model system of porcine post-weaning colibacillosis, and in doing so to assess the primary relationship of enterotoxigenic Escherichia coli to post-weaning diarrhoea and digestive disorders as encountered in the field. Six sequential experiments were carried out using 168 SPF piglets weaned into an optimal controlled environment at 28 days of age. The piglets were allocated to 23 treatment groups, 17 of which were inoculated either orally or intragastrically with enterotoxigenic strains of E. coli (LT+, STI+, STII+) possessing adhesive factors including K88 (F4). The piglets were challenged either once (Day 4 post-weaning) or on several days post-weaning, with the challenge load for each inoculation varying from 10(8) to 10(12) CFU. Overall 14.5% of inoculated pigs developed severe illness and died: these had lesions in their digestive tracts typical of colibacillosis. Diarrhoea occurred on at least 1 day in 50% of inoculated pigs, but was transient (1.7 days on average), appeared very soon after challenge (sometimes within half a day), and was accompanied by signs of depression and low weight gain. Generally a prompt recovery then occurred. In the second 2 weeks post-inoculation daily weight gain reached the same level in most inoculated groups of pigs as in the uninoculated controls. Only a small number of pigs developed a chronic enteritis lasting several days, as is typically observed in field cases. Diarrhoea was more common in the piglets that were tested adhesive positive to the K88 fimbriae receptor, but the disorders were no more severe in these animals. The response of all pigs depended primarily on the inoculum used, and especially on the challenge load. Although enterotoxigenic E. coli are clearly important in the aetiology of post-weaning diarrhoea, other factors are also required for the production of the chronic post-weaning digestive disorders and ill-thrift that are commonly encountered in commercial piggeries.

Animals↗

PubMed1984

Anteroposterior gradients in cerebral glucose use in schizophrenia and affective disorders.

Local cerebral uptake of deoxyglucose labeled with fluorine 18 was measured by positron emission tomography in 16 patients with schizophrenia and 11 patients with affective disorder. Patients received no medication a minimum of 14 days and an average of 39.8 days. The subjects were administered the deoxyglucose 18F just before receiving a 34-minute 1/s series of unpleasant electrical stimuli to the right forearm while resting with eyes closed in a darkened, acoustically attenuated psychophysiologic testing chamber. Following monitored stimulation in the controlled environment, subjects were scanned and images converted to values of glucose use in micromoles per 100 g per minute according to Sokoloff's model. Data were analyzed with a four-way analysis of variance (ANOVA) with independent groups (normals, schizophrenics, and affectives) and repeated measures for slice level (supraventricular, midventricular, and infraventricular), hemisphere (right, left), and anteroposterior position (four sectors). Both normal subjects and patients showed a significant anteroposterior gradient in glucose use with highest values in the frontmost sector. Patients both with schizophrenia and with affective illness showed less of an anteroposterior gradient especially at superior levels, which was statistically confirmed by ANOVA. Absolute glucose levels in patients, which were actually higher in posterior regions rather than lower in frontal regions, were the largest contributors to the effect. Neither group differences in whole brain glucose use nor left-right asymmetries reached statistical significance. These results are consistent with our earlier reports of a relative hypofrontal function in schizophrenia compared with controls. This report extends this finding to affective illness, sharing a lack of diagnostic specificity with many biologic measures.

Adult↗

PubMed1998

Response of potatoes to nitrogen concentrations differ with nitrogen forms.

Two separate experiments were conducted to investigate plant growth and mineral composition of potatoes (Solanum tuberosum L.) at varied solution concentrations of nitrate (NO3-) and ammonium (NH4+). Each experiment evaluated five nitrogen (N) concentrations of 0.5, 2, 4, 8, and 12 mM, which were maintained with a non-recirculating nutrient film system in controlled environment. Plants were harvested on day 42 with NO3-; and day 35 with NH4+ after transplanting of tissue culture plantlets, and growth measurements were taken as leaf area, tuber number, and dry weights of different parts. With NO3-, plant growth was greatest and similar at 2, 4, and 8 mM of N whereas with NH4+, plant growth was best only at 2 and 4 mM of N. At 12 mM of N, plants exhibited interveinal ammonium toxicity with NH4+ nutrition, but healthy growth appearance with NO3- nutrition. With either N form, total N concentrations in tissues tended to increase with increased N concentrations, and tissue phosphorus (P) concentrations were reduced at 0.5 and 2 mM of N. Tissue concentrations of calcium (Ca), magnesium (Mg), and sulfur (S) changed only slightly at particular N concentrations, yet changed substantially with different N forms. The data indicate that the optimal ranges of N concentrations in both solution and tissues are wider and higher with NO3- than with NH4+ nutrition, and thus a careful control of NH4+ concentrations is necessary to minimize possible ammonium toxicity to potato plants.

Biomass↗

PubMed1980

On the Reason for the Different Photosynthetic Rates of Seedlings of Pinus silvestris and Betula verrucosa.

The growth and net photosynthetic properties of seedlings of Pinus silvestris L. and Betula verrucosa Ehrh., grown under identical conditions in a controlled environment chamber, were compared. The relative growth rate of birch was about twice that of pine. The rates of in situ net photosynthesis were 1.50 and 2.30 micromoles CO(2) meter(-2) second(-1) and the photosynthetic quantum yields under light-limiting conditions were 0.022 and 0.032 for pine and birch, respectively. The total leaf surface areas were used for calculating the CO(2) flux densities. The difference in the rates of in situ net photosynthesis depended equally on morphological and metabolic factors. It was assumed that a pronounced mutual shading and an unfavorable leaf inclination made the pine seedlings less efficient in absorbing the unidirectional light of the climate chamber than the broadleaved seedlings of birch. Both pine and birch were adapted to the growth conditions so the flux densities of absorbed quanta were rate-limiting for in situ net photosynthesis. It was concluded that the difference in the photosynthetic quantum yields (i.e. the linear slope of the photosynthetic light curve) of the two species defined the metabolically controlled part of the difference in the rate of in situ net photosynthesis. The quantum yield of pine was lower than that of birch and was partly explained by pine having a higher rate of photorespiration than birch. The remaining difference was most likely controlled by the properties of the chloroplast thylakoids, e.g. energy transfer efficiency between pigments, photosynthetic electron transport, or coupling between electron transport and photophosphorylation.

Journal Article↗

PubMed2002

Prevalence of cervical facet joint pain in chronic neck pain.

Neck pain is considered to be one of the most common chronic pain conditions in modern society. Various structures identified as capable of transmitting pain in the cervical spine include facet joints, intervertebral discs, nerve root dura, ligaments, fascia, and muscles. The prevalence of cervical facet joint pain in patients with chronic pain after whiplash has been determined as 54% to 60%. However, the prevalence of chronic cervical facet joint pain has not yet been determined in a heterogenous population or in patients with cervical spine pain of idiopathic origin in a controlled environment. This study evaluated 160 patients seen in one interventional pain management practice in a non-university setting. Cervical facet joints were investigated with diagnostic blocks using lidocaine 1% preservative free initially, followed by bupivacaine 0.25%, usually 2 to 4 weeks apart. The study population consisted of 76 women and 30 men aged 43 +/- 13 years of age (mean +/- SD). Mode of onset of neck pain was determined as following a traumatic incident in 48% of the patients, whereas it was with gradual onset without an identifiable specific incident in the remaining 55 patients (52%). Eighty-one or 70% of the patients (70%) reported a definite response to lidocaine blocks. Confirmatory blocks with bupivacaine were performed in 81 patients with 64 patients with 60% of the total sample, or 79%, of the lidocaine-positive group reporting definite response with improvement in their pain. Thus, a prevalence rate of facet joint pain in chronic neck pain was determined to be 60% (95% CI, 50%-70%), with a false positive rate of controlled diagnostic blocks of 40% (95% CI, 34%-46%).

Journal Article↗

PubMed1990

Residential laboratory research: a multidimensional evaluation of the effects of drugs on behavior.

The data presented point to the importance of studying drug effects under conditions similar to those in which drugs are taken outside of the laboratory. Interactions between the reinforcing and other direct effects of these drugs, as well as their interactions with ongoing environmental events can only be evaluated under such conditions. These data support the utility of a residential research facility for the investigation of substance use and its effects under conditions which approximate those in which people live outside of the laboratory. This unique laboratory, designed for continuous observation of human behavior over extended periods of time, provides a controlled environment with the flexibility for establishing a range of subject behaviors, and the ability to simultaneously monitor a wide range of individual and social behavior patterns. We can study regulation of drug intake and its effects, both within a day and over days, assessing the effects of experimental manipulations on the patterning of self-administration behavior as well as the performance of a range of other behaviors as a function of drug self-administration. The design of such studies is a logical extension of basic preclinical research, as well as more traditional human behavioral pharmacology research. Although little data are yet available on drug-related "hangovers" or "morning after" effects, it should be clear that this residential laboratory would provide ideal experimental conditions for such research. We have shown that subjects will exhibit stable patterns of drug self-administration which are sensitive to systematic manipulation of variables. Therefore, we are in the position of being able to evaluate longer term effects on performance of drug-taking behavior as it occurs under conditions approximating the natural ecology. The examples of data collected in the laboratory have demonstrated that drug effects are not a unitary phenomenon, but instead depend on ongoing behaviors as well as pharmacological variables such as drug and dose. If we are going to evaluate drugs and the way in which they affect workplace behavior, we must carry out our evaluation under conditions which approximate those in which people might be using them, while at the same time controlling extraneous variables and protecting the participants from possible deleterious effects. We have shown that drugs, such as marijuana and amphetamine, have divergent effects that are influenced by both situational and behavioral factors. A thorough evaluation of the effects of any drug on behavior is, therefore, dependent on the evaluation of the drug's effects under the conditions in which it is likely to be taken.

Adult↗

PubMed1998

Differential rearing affects corpus callosum size and cognitive function of rhesus monkeys.

This study investigated the effects of different rearing conditions on neural and cognitive development of male rhesus monkeys (Macaca mulatta). Infants raised individually in a nursery from 2 to 12 months of age (NURSERY, n=9) were compared to age-matched infants raised in a semi-naturalistic, social environment (CONTROL, n=11). Various brain regions were measured by MRI. Although overall brain volumes did not differ between NURSERY and CONTROL animals, corpus callosum (CC) size, measured in mid-sagittal sections, was significantly decreased in the NURSERY group. Group differences were most evident in the posterior aspects of the corpus callosum and appeared to result from changes in the number of cross-hemispheric projections rather than from a decrease in cortical gray matter volume. The decrease in corpus callosum size in the NURSERY animals persisted after 6 months of social housing in a peer-group. Rearing group differences were not found in other structures analyzed, including the hippocampus, cerebellum and anterior commissure. In cognitive testing, NURSERY animals had more difficulty acquiring the delayed non-matching to sample (DNMS) task, but showed no deficits in subsequent memory performance when a 2 or 10 min delay was imposed. The NURSERY infant monkeys were also impaired in object, but not in spatial, reversal learning, although there were no differences in a simple object discrimination task. The cognitive deficits exhibited by the NURSERY animals were significantly correlated with the alterations found in the CC. In summary, rearing environment was associated with sustained differences in cross-hemispheric projections, white matter volume and cognitive performance.

Animals↗

PubMed2003

A sequential approach to risk assessment of transgenic plants expressing protease inhibitors: effects on nontarget herbivorous insects.

Protease inhibitors expressed in transgenic plants can provide enhanced levels of resistance to important pest species. A sequential approach for testing the effects of protease inhibitor-expressing crops on nontarget herbivorous insects has been developed. The approach consists of five tiers. The first two tiers comprise the selection phase. In tier one, field surveys are used to characterise the nontarget invertebrate fauna of a crop. In tier 2, histochemical assays are used to identify the subset of herbivores with a particular class of digestive proteolytic enzymes. In the assessment phase a combination of laboratory 'worst-case scenario' studies (tier 3) and controlled environment or small-scale field trials (tier 4) are used to evaluate the impact of the protease inhibitor-expressing plants on the selected nontarget species. In the final tier, field trials are used to compare the relative effect of transgenic plants and current management practices, such as pesticide use, on selected species. The first four tiers of the approach are described using potatoes expressing cystatins, a family of cysteine proteinase inhibitors, as an example. Although the plants have enhanced levels of resistance to potato cyst nematodes (PCN), Globodera pallida and Globodera rostochiensis, the results establish that they have negligible impact on the nontarget herbivorous insect, Eupteryx aurata.

Animals↗

PubMed1984

Positron emission tomographic image measurement in schizophrenia and affective disorders.

Two analytical methods for assessing regional glucography with positron emission tomography were compared in 16 patients with schizophrenia and 11 patients with affective disorders. Patients were off all medication a minimum of 14 days and an average of 39.8 days. The subjects were administered fluorine-18-labeled 2-deoxyglucose just before receiving a 34-minute one-per-second series of unpleasant electrical stimuli to their right forearm while resting with their eyes closed in a darkened, acoustically attenuated psychophysiological testing chamber. Following monitored stimulation in the controlled environment, the subjects were scanned and the images were converted to values of glucose use in micromoles per 100 grams per minute, according to Sokoloff's model. Data were analyzed by a four-way analysis of variance (ANOVA) for independent groups (normal subjects, schizophrenic patients, and patients with affective disorders) and for repeated measures of slice level (supraventricular, midventricular , and infraventricular ), hemisphere (right, left), and anteroposterior position (four sectors). Normal individuals and patient groups both showed a significant anteroposterior gradient in glucose use, with the highest values in the sector farthest to the front. Patients with schizophrenia and those with affective illnesses showed less of an anteroposterior gradient than normal individuals, especially at superior levels, which was statistically confirmed by ANOVA. Neither the group differences in whole-brain glucose use nor the left-right asymmetries reached statistical significance. A second technique, involving reconstruction of the lateral cortical surface, also revealed differences between schizophrenics and normal individuals in the superior frontal cortex. These results are consistent with our earlier reports of a relative hypofrontal function in schizophrenia compared with controls; they also extend the finding to the affective illnesses, the other group of major psychoses.

Adult↗

PubMed1989

Short-term effects of temazepam in the EEGs of healthy volunteers.

In this study effects of temazepam on the EEGs of 10 healthy volunteers were detected using a standardized EEG registration procedure applied in a controlled environment. The EEGs were recorded both before and after administration of 20 mg temazepam as well as before and after placebo. A mean power spectrum was computed for each EEG from the 'eyes closed' condition, and the Student t test was used to detect differences in the spectra of the pre- and posttreatment EEGs in both placebo and drug conditions. For all 10 subjects the drug condition was easily distinguishable from the placebo condition based on the results of the t test.

Adult↗

PubMed2000

Comparison of selected perceptual variables for backpacks with internal and external frames.

Differences in perceptions of comfort, exertion, balance, and heart rate were investigated with two types of backpack. Subjects were 20 male volunteers (M age = 24.3 yr., SD: 3.6, M height = 180.02 cm, SD: 8.0, and M weight = 86.46 kg, SD: 14.84). Following oral briefing and practice trials, each subject was fitted at random with either an internal- or external-frame backpack containing 18.2 kg. By random, cross-over design, subjects completed a 30-m simulated hiking trial consisting of 16 separate obstacles designed to resemble actual off-trail hiking. Trials were conducted in a controlled environment with the walking intensity regulated by a metronome. Upon completion of each trial, the subjects rated the experience on perceived comfort, balance and stability, and rating of perceived exertion. Heart rate was recorded immediately prior to and following each trial. Analysis yielded a significant difference only on rating of perceived exertion in favor of the internal-frame backpack. Under limited circumstances, these data suggest that both types of backpacks provide similar comfort and balance and stability; however, internal frames in backpacks may reduce perceived exertion during short, demanding hikes.

Adult↗

PubMed1997

Minimisation of microbial contamination for potential islet xenografts using specific pathogen-free pigs and a protected environment during tissue preparation.

One major risk of islet xenotransplantation is transmission of infections. We thus compared microbial contamination during preparation of islets from 4 pigs conventionally breeded and slaughtered or 8 specific pathogen free (SPF) pigs, and different environmental conditions during pancreas excision. Pancreas harvested in a slaughterhouse (for conventional pigs) or in a protected autopsy room (for SPF pigs) were soaked in betadine solution and submitted to enzymatic digestion with collagenase. Islets were purified on histopaque gradient with a COBE 2991 processor. For each step of the process, a 10 ml aliquot was harvested and microbial contamination was analysed. For all animals, contamination of livers, which were not soaked in betadine solution, was also examined. Analysis of livers from the 4 conventional pigs showed polymicrobial contaminations (1,122 +/- 841 CFU/mg) with several species of Staphylococcus, Streptococcus, Bacillus and Enterobacteriaceae. For these conventional pigs, soaking of pancreas in betadine solution and presence of antibiotics in all media decreased the pancreatic contamination compared to hepatic contamination, but were unable to suppress it, as transport solution and crude suspension obtained after the digestion step with collagenase showed persistent contamination (9.7 +/- 2.4 and 10.5 +/- 4 CFU/ml, respectively). After islet purification by histopaque gradient, no medium remained contaminated. During analysis of the 8 SPF pigs, no liver exhibited contamination. Analysis of medium from each preparation step showed complete absence of contamination for 7 pancreases. Only one contamination with Staphylococcus simulans was observed for one pancreas in transport solution (6 CFU/ml), and persisted in digestion medium (16 CFU/ml). Finally, all purified suspensions were completely sterile. In conclusion, breeding conditions of pig islet donors, and controlled environment for pancreas excision, considerably influence the risk of microbial contamination. In order to limit the risk, SPF pigs are a suitable and compulsory source of islets.

Animals↗

PubMedDate not supplied

Hemodynamic and pressure-volume responses to continuous and pulsatile ventricular assist in an adult mock circulation.

This study investigated the hemodynamic and left ventricular (LV) pressure-volume loop responses to continuous versus pulsatile assist techniques at 50% and 100% bypass flow rates during simulated ventricular pathophysiologic states (normal, failing, recovery) with Starling response behavior in an adult mock circulation. The rationale for this approach was the desire to conduct a preliminary investigation in a well controlled environment that cannot be as easily produced in an animal model or clinical setting. Continuous and pulsatile flow ventricular assist devices (VADs) were connected to ventricular apical and aortic root return cannulae. The mock circulation was instrumented with a pressure-volume conductance catheter for simultaneous measurement of aortic root pressure and LV pressure and volume; a left atrial pressure catheter; a distal aortic pressure catheter; and aortic root, aortic distal, VAD output, and coronary flow probes. Filling pressures (mean left atrial and LV end diastolic) were reduced with each assist technique; continuous assist reduced filling pressures by 50% more than pulsatile. This reduction, however, was at the expense of a higher mean distal aortic pressure and lower diastolic to systolic coronary artery flow ratio. At full bypass flow (100%) for both assist devices, there was a pronounced effect on hemodynamic parameters, whereas the lesser bypass flow (50%) had only a slight influence. Hemodynamic responses to continuous and pulsatile assist during simulated heart failure differed from normal and recovery states. These findings suggest the potential for differences in endocardial perfusion between assist techniques that may warrant further investigation in an in vivo model, the need for controlling the amount of bypass flow, and the importance in considering the choice of in vivo model.

Adult↗

PubMed1982

Short-term respiratory effects of 0.12 ppm ozone exposure in volunteers with chronic obstructive pulmonary disease.

Twenty-five volunteers with chronic obstructive pulmonary disease of mild to moderately severe degree underwent 1-h exposures to 0.12 ppm ozone (O2) in purified air with intermittent mild exercise. Their responses were assessed in terms of forced expiratory performance, ear oximetry, and reported symptoms. Control studied consisted of similar exposures to purified air alone. Control studies were separated from O2 exposures by 1 month, and the order was randomized. All studies took place in a controlled-environment chamber, and were preceded by approximately 1 h of rest in a purified-air environment. No significant disturbances in forced expiratory performance or symptoms attributable to O2 exposure were found. A slight but significant tendency to decreased arterial hemoglobin oxygen saturation (SaO2) during exercise in O2 was observed. The decrement in SaO2 with O2 relative to clean air (mean 1.3%) was near the limit of resolution of the ear oximeter test and was detected by signal averaging, thus its physiologic or clinical significance is uncertain.

Adult↗

PubMed2006

Cost-effectiveness of duloxetine versus routine treatment for U.S. patients with diabetic peripheral neuropathic pain.

UNLABELLED: The purpose of this study was to compare the cost-effectiveness of duloxetine versus routine treatment in management of diabetic peripheral neuropathic pain (DPNP). Two hundred thirty-three patients with DPNP who completed a 12-week, double-blind, placebo-controlled, randomized, multicenter duloxetine trial were re-randomized into a 52-week, open-label trial of duloxetine 60 mg twice daily versus routine treatment. Routine treatment included pain management therapies. Effectiveness was measured by using the bodily pain domain (BP) of the Medical Outcomes Study Short Form 36 (SF-36). Costs were analyzed from 3 perspectives: third party payer (direct medical costs), employer (direct and indirect medical costs), and societal (patient's out-of-pocket costs and total medical costs). Costs of study medications were not included because of limited data. Bootstrap method was applied to calculate statistical inference of the incremental cost-effectiveness ratio (ICER). Routine treatment most frequently used included gabapentin (56%), venlafaxine (36%), and amitripytline (15%). From employer and societal perspectives, duloxetine was cost-effective (ICER= -342 dollars and -429 dollars, respectively, per unit of SF-36 BP; both P <or= .03) and the dominant therapy compared with routine DPNP treatment (both P < .05). From payer perspective, duloxetine trended toward cost-effectiveness (ICER= -249 dollars per unit of SF-36 BP; P <or= .06). These results, however, reflect the controlled environment of a clinical trial. An analysis of real-world data would be beneficial. PERSPECTIVE: Evaluation of the cost and benefit of new pharmacologic treatments is highly desired by decision makers. From both employer perspective and societal perspective (including patient's out-of-pocket costs), this study demonstrated that duloxetine was more cost-effective than routine treatment in management of DPNP.

Adrenergic Uptake Inhibitors↗

PubMed2004

Influence of nitrogen nutrition management on biomass partitioning and nitrogen use efficiency indices in hydroponically grown potato.

The National Aeronautics and Space Administration (NASA) has been conducting controlled environment research with potatoes (Solanum tuberosum L.) in recirculating nutrient film technique (NFT)-hydroponic systems as a human life support component during long-duration spaceflight. Standard nutrient solution management approaches include constant pH regulation with nitric acid (HNO3) and daily adjustment of electrical conductivity (EC) equivalent to half-strength modified Hoagland's solution, where nitrate (NO3-) is the sole nitrogen (N) source. Although tuber yields have been excellent with such an approach, N use efficiency indices are expected to be low relative to tuber biomass production. Furthermore, the high amount of N used in NFT-hydroponics, typically results in high inedible biomass, which conflicts with the need to minimize system mass, volume, and expenditure of resources for long-duration missions. More effective strategies of N fertilization need to be developed to more closely match N supply with demand of the crop. Hence, the primary objective of this study was to identify the optimal N management regime and plant N requirement to achieve high yields and to avoid inefficient use of N and excess inedible biomass production. In separate 84-day cropping experiments, three N management protocols were tested. Treatments which decreased NO3(-)-N supply indirectly through lowering nutrient solution EC (Expt. I), or disabling pH control, and/or supplying NH4(+)-N (Expt. III) did not significantly benefit tuber yield, but did influence N use efficiency indices. When supplied with an external 7.5 mM NO3(-)-N for the first 42 days after planting (DAP), lowered to 1.0 mM NO3(-)-N during the final 42 days (Expt. II), plants were able to achieve yields on par with plants which received constant 7.5 mM NO3(-)-N (control). By abruptly decreasing N supply at tuber initiation in Expt. II, less N was taken up and accumulated by plants compared to those which received high constant N (control). However, proportionately more plant accumulated N was used (N use efficiency) to produce tuber biomass when N supply was abruptly lowered at tuber initiation in Expt. II. Hence, a hydroponic nutrient solution N management system may be modified to elicit greater plant N-use while maintaining overall high tuber yield as opposed to achieving high tuber yields through excess N supply and shoot growth.

Biomass↗

PubMed2002

Variability in conversion of beta-carotene to vitamin A in men as measured by using a double-tracer study design.

BACKGROUND: The vitamin A activity of beta-carotene is variable and surprisingly low in women. The reasons for this are not well understood. The vitamin A activity of beta-carotene in men is still uncertain. Contributions of dietary factors compared with individual traits are largely unknown. OBJECTIVE: Our objective was to measure the intrinsic variability in the vitamin A activity of beta-carotene among healthy, well-fed men living in a controlled environment. DESIGN: We used a double-tracer test-retest design. We dosed 11 healthy men orally with 30 micromol hexadeuterated (D6) retinyl acetate (all-trans-19,19,19,20,20,20-[2H6]retinyl acetate) and then with 37 micromol D6 beta-carotene (19,19,19,19',19',19'-[2H6]beta-carotene) 1 wk later. Doses were taken with breakfasts containing 16 g fat. We measured D6 retinol, D6 beta-carotene, and trideuterated (D3) retinol (derived from D6 beta-carotene) concentrations in plasma. Areas under the plasma concentration x time since dosing curves (AUCs) were determined for D6 retinol, D6 beta-carotene, and D3 retinol. RESULTS: All men had detectable D6 retinol concentrations in plasma. The mean (+/-SE) absorption of D6 beta-carotene in all subjects was 2.235 +/- 0.925%, and the mean conversion ratio was 0.0296 +/- 0.0108 mol retinol to 1 mol beta-carotene. Only 6 of 11 men had sufficient plasma concentrations of D6 beta-carotene and D3 retinol that we could measure. The mean absorption of D6 beta-carotene in these 6 subjects was 4.097 +/- 1.208%, and the mean conversion ratio was 0.0540 +/- 0.0128 mol retinol to 1 mol beta-carotene. CONCLUSION: The vitamin A activity of beta-carotene, even when measured under controlled conditions, can be surprisingly low and variable.

Absorption↗