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PubMed2002

Expression of a bacterial carotene hydroxylase gene (crtZ) enhances UV tolerance in tobacco.

Carotenoids are essential components of the photosynthetic apparatus involved in plant photoprotection. To investigate the protective role of zeaxanthin under high light and UV stress we have increased the capacity for its biosynthesis in tobacco plants (Nicotiana tabacum L. cv. Samsun) by transformation with a heterologous carotenoid gene encoding beta-carotene hydroxylase (crtZ) from Erwinia uredovora under constitutive promoter control. This enzyme is responsible for the conversion of beta-carotene into zeaxanthin. Although the total pigment content of the transgenics was similar to control plants, the transformants synthesized zeaxanthin more rapidly and in larger quantities than controls upon transfer to high-intensity white light. Low-light-adapted tobacco plants were shown to be susceptible to UV exposure and therefore chosen for comparative analysis of wild-type and transgenics. Overall effects of UV irradiation were studied by measuring bioproductivity and pigment content. The UV exposed transformed plants maintained a higher biomass and a greater amount of photosynthetic pigments than controls. For revelation of direct effects, photosynthesis, pigment composition and chlorophyll fluorescence were examined immediately after UV treatment. Low-light-adapted plants of the crtZ transgenics showed less reduction in photosynthetic oxygen evolution and had higher chlorophyll fluorescence levels in comparison to control plants. After 1 h of high-light pre-illumination and subsequent UV exposure a greater amount of xanthophyll cycle pigments was retained in the transformants. In addition, the transgenic plants suffered less lipid peroxidation than the wild-type after treatment with the singlet-oxygen generator rose bengal. Our results indicate that an enhancement of zeaxanthin formation in the presence of a functional xanthophyll cycle contributes to UV stress protection and prevention of UV damage.

Adaptation, Physiological↗
PubMed2000

Glial-derived growth factor signaling pathway in infantile hypertrophic pyloric stenosis.

BACKGROUND/PURPOSE: Glial-derived growth factor (GDNF), which is the ligand of RET is reported to be essential for the development of enteric nervous system. A GDNF knockout mouse model has shown that the gastric region is a critical passing site between GDNF-RET-independent neuroblasts (colonizing the esophagus) and GDNF-RET-dependent neuroblasts (colonizing the small and large bowel). The earliest GDNF site of production is the mesenchyme and the outer smooth muscle cell (SMC) layer of the developing bowel. In the mature gastrointestinal tract the presence of GDNF is restricted to enteric glial cells. The aim of this study was to investigate the expression of GDNF and RET in infantile hypertrophic pyloric stenosis (IHPS). METHODS: Full-thickness muscle biopsy specimens were obtained from 8 IHPS patients at pyloromyotomy and from 8 age-matched controls without gastrointestinal disease. Indirect immunohistochemistry was performed using avidin-biotin-peroxidase complex method with anti-GDNF and anti-RET antibodies. Quantitative analysis was performed using sandwich-type enzyme-linked immunosorbent assay (ELISA) for GDNF. RESULTS: GDNF- and RET-positive nerve fibers were absent or markedly reduced in IHPS compared with controls. GDNF was expressed strongly by smooth muscle cells of both muscular layers in IHPS, whereas no GDNF expression was detected in pyloric muscle of controls. The quantity of total GDNF in IHPS was significantly higher than in controls (P < .01). CONCLUSIONS: The lack or markedly decreased number of GDNF-positive nerve fibers in IHPS supports the hypothesis of a selective immaturity of the enteric glia in the muscular layers in IHPS. The strong expression of GDNF in smooth muscle cells in IHPS and the increased levels of GDNF in IHPS suggest a compensatory mechanism by which the smooth muscle cells continue to produce GDNF until maturation of the enteric glial cells occurs.

Drosophila Proteins↗
PubMed2006

The type-reproduction number T in models for infectious disease control.

A ubiquitous quantity in epidemic modelling is the basic reproduction number R(0). This became so popular in the 1990s that 'All you need know is R(0)!' became a familiar catch-phrase. The value of R(0) defines, among other things, the control effort needed to eliminate the infection from a homogeneous host population, but can be misleading when applied to a heterogeneous population for the same purpose. We have defined the type-reproduction number T for an infectious disease, and shown that this not only has the required threshold behaviour, but also correctly determines the critical control effort for heterogeneous populations. The two quantities coincide for homogeneous populations. In this paper we further develop the new threshold quantity as an indicator of control effort required in a system where multiple types of individuals are recognised when control targets a specific type.

Algorithms↗
PubMed2001

Evidence for common controls over inheritance of bone quantity and body size from segregation analysis in a pedigreed colony of nonhuman primates (Macaca nemestrina).

The genetic determinants of bone mineral quantity and body size and their postulated interaction are just beginning to be elucidated. The heritability of bone quantity and its relationship to components of body size were therefore investigated using segregation analysis applied to a large pedigreed nonhuman primate (Macaca nemestrina) breeding colony. The colony consisted of 216 females and 16 males with uniform dietary histories, environmental conditions, and rearing of offspring apart from the mother to minimize familial aggregation. Bone quantity (bone mineral content and spinal areal density) was measured by dual-energy X-ray absorptiometry (DXA). Size included measures of body mass, length, breadth, and a composite index. Body mass was determined from both body weight and lean body mass by DXA. Length was assessed by measuring trunk and thigh lengths, and breadth by measuring chest circumference and bitrochanteric width. A composite index of size was also calculated from a linear function of trunk and thigh lengths, chest circumference and bitrochanteric width, and lean body mass. Traits of bone quantity and size were highly correlated (r = 0.56-0.96, p < 0.001). Significant (p < or = 0.03) univariate heritabilities were found for spine bone mineral density (SPBMD; h(2) = 0.66) and whole body bone mineral content (WBBMC; h(2) = 0.40) and size measures of length (trunk h(2) = 0.71, thigh h(2) = 0.65), breadth (bitrochanteric width h(2) = 0.31), lean body mass (LEAN; h(2) = 0.37), and the composite index of size (SIZE-PC, h(2) = 0.49) adjusted for demographic variables. The data were also subjected to an analysis of bivariate genetic correlations and factor analysis, both of which suggested a robust interaction between body size and bone quantity. Bivariate genetic correlations between body size and the bone quantities WBBMC, SBMD, and spine bone mineral content (SPBMC) were high (e.g., using LEAN as a measure of size, r = 0.57, 0.41, and 0.57, respectively). Factor analysis showed that 80% of the phenotypic and 72% of the genetic variances of all traits were accounted for by a single factor, suggesting common genetic controls operative over bone quantity and size.

Absorptiometry, Photon↗
PubMed1994

Transdermal delivery of metoprolol by electroporation.

Electroporation, i.e., the creation of transient "pores" in lipid membranes leading to increased permeability, could be used to promote transdermal drug delivery. We have evaluated metoprolol permeation through full thickness hairless rat skin in vitro following electroporation with an exponentially decaying pulse. Application of electric pulses increased metoprolol permeation as compared to diffusion through untreated skin. Raising the number of twin pulses (300 V, 3 ms; followed after 1 s by 100 V, 620 ms) from 1 to 20 increased drug transport. Single pulse (100 V, 620 ms) was as effective as twin pulse application (2200 V, 1100 V or 300 V, 3 ms; followed after 1 s by 100 V, 620 ms). In order to investigate the effect of pulse voltage on metoprolol permeation, 5 single pulses (each separated by 1 min) were applied at varying voltages from 24 to 450 V (pulse time 620 ms). A linear correlation between pulse voltage and cumulative metoprolol transported after 4 h suggested that voltage controls the quantity of drug delivered. Then, the effect of pulse time on metoprolol permeation was studied by varying pulse duration of 5 single 100 V pulses from 80 to 710 ms (each pulse also separated by 1 min). Cumulative metoprolol transported after 4 h increased linearly with the pulse time. Therefore, pulse time was also a control factor of the quantity of drug delivered but to a lesser extent than the voltage at least at 100 V.(ABSTRACT TRUNCATED AT 250 WORDS)

Administration, Cutaneous↗
PubMed1976

Estrogen-containing oral contraceptive agents. A basis for their thrombogenicity.

The mechanism whereby estrogen-containing contraceptives facilitate thrombosis is obscure, and published data concerning their effect on antithrombin III are conflicting. Plasma samples were examined for the quantity of antithrombin III and activated factor X (Xa) inhibitory activity among 57 women receiving oral contraceptives and 48 controls. The quantity of antithrombin III in both groups was normal. In contrast, Xa inhibitory activity was significantly reduced (P less than .001) among patients taking oral contraceptives, compared to controls. Heparin sodium added to plasma from patients taking contraceptives raised Xa inhibitory activity toward or above normal without changing the quantity of antithrombin III. The effect of estrogen is not to decrease the quantity of plasma antithrombin III, but rather to diminish plasma Xa inhibitory activity, an effect that can be abolished by heparin.

Adolescent↗
PubMed1984

Rate control of phosphorylation-coupled respiration by rat liver mitochondria.

Liver mitochondria provided with an oxidizable substrate, ATP, oxygen, and an ADP-generating system (soluble F1-ATPase) were used to reevaluate the rate-controlling step(s) intrinsic to all of the processes of mitochondrial oxidative phosphorylation. The quantity termed "control strength" (C), previously defined as the fractional change in flux through a (system) induced by a fractional change in the concentration of an individual enzyme in the system, has been used to evaluate rate-influencing steps in this overall process by carefully defining the dimensions of the "system" under analysis. If the system is defined by a suspension of mitochondria provided with substrates, plus an extrinsic ADP-generating process (ATPase), the value of C of the latter for the overall process of phosphorylation-linked respiration is near 1.0 until the capacity of the mitochondria to phosphorylate ADP is approached, after which C for the soluble ATPase becomes zero as the maximum capacity for phosphorylation is attained. Carboxyatractyloside was found only marginally to inhibit respiration stimulated by ATPase, even when a large percentage of adenine nucleotide translocase molecules were immobilized. The relative lack of effect of carboxyatractyloside on phosphorylating respiration is explained by the readjustment of the concentration of one of the substrates (ADP) and an inhibitor (ATP), which results from inhibition of adenine nucleotide translocase. The residual blunted inhibition of respiration is explained by product inhibition of the ADP-regenerating ATPase, and not necessarily to any intrinsically mitochondrial intermediate process. The system being evaluated can be redefined to include only the processes intrinsic to mitochondria. This can be achieved by providing exactly comparable substrate concentrations to the mitochondria under comparable incubation conditions. Under these conditions, the adenine nucleotide translocase is the principal, if not the only, rate-controlling step in the overall process of oxidative phosphorylation until a new rate-limitation is attained (ATP synthesis). These data are consistent with the conclusion that, at intermediate rates of phosphorylation-coupled respiration, the extramitochondrial ATP/ADP ratio regulates this process through its kinetic effects on the catalytic properties of the adenine nucleotide translocase.

Adenosine Diphosphate↗
PubMed2001

Selective neurotrophin deficiency in infantile hypertrophic pyloric stenosis.

BACKGROUND/PURPOSE: Increasing evidence suggests that the enteric nervous system is under the control of neurotrophins. Nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3), and neurotrophin-4/5 (NT-4/5), promote differentiation, growth, and survival of various central and peripheral nervous system neurons. The biological effects of neurotrophins are mediated by the interactions with high-affinity tyrosine kinase receptors (TrkA, TrkB, TrkC). Recently, abnormalities of intramuscular innervation have been reported in infantile hypertrophic pyloric stenosis (IHPS). To further understand the reported abnormalities in pyloric innervation in IHPS, the authors analyzed the expression of Trk receptors and the neurotrophins content in IHPS. METHODS: Full-thickness muscle biopsy specimens were obtained from 8 IHPS patients (age range, 23 to 41 days) at pyloromyotomy and from 8 age-matched controls without gastrointestinal disease at autopsy performed within 12 hours after death. Indirect immunohistochemistry was performed using ABC (Avidin Biotin peroxidase Complex) method with anti-Trk specific antibodies (A,B,C). Quantitative analysis was performed using sandwich-type ELISA for NGF, BDNF, NT-3, and NT-4/5. RESULTS: The intensity of staining of the myenteric plexus for TrkA, TrkB, and TrkC was similar among IHPS and controls. There was a lack of TrkA-positive nerve fibers in IHPS compared with controls. The quantity of total NGF, NT-3, and BDNF in IHPS was significantly lower than in controls. CONCLUSIONS: The reduced production of neurotrophins in IHPS may be responsible for the delay in the functional and structural maturation of pyloric innervation in IHPS. The lack of TrkA-positive nerve fibers in pyloric muscle may explain the abnormal intramuscular innervation in IHPS.

Analysis of Variance↗
PubMed1998

Opposite roles of apolipoprotein E in normal brains and in Alzheimer's disease.

We have characterized the interaction between apolipoprotein E (apoE) and amyloid beta peptide (Abeta) in the soluble fraction of the cerebral cortex of Alzheimer's disease (AD) and control subjects. Western blot analysis with specific antibodies identified in both groups a complex composed of the full-length apoE and Abeta peptides ending at residues 40 and 42. The apoE-Abeta soluble aggregate is less stable in AD brains than in controls, when treated with the anionic detergent SDS. The complex is present in significantly higher quantity in control than in AD brains, whereas in the insoluble fraction an inverse correlation has previously been reported. Moreover, in the AD subjects the Abeta bound to apoE is more sensitive to protease digestion than is the unbound Abeta. Taken together, our results indicate that in normal brains apoE efficiently binds and sequesters Abeta, preventing its aggregation. In AD, the impaired apoE-Abeta binding leads to the critical accumulation of Abeta, facilitating plaque formation.

Alzheimer Disease↗
PubMed1996

Changes in poly(A) tail length of arginine vasotocin messenger ribonucleic acid in the hypothalamus of water-deprived chickens.

The effects of water deprivation on the secretion of vasotocin (AVT) and expression of the AVT gene were studied in White Leghorn cockerels. Animals deprived of water for 4 days were compared with normally hydrated controls. Blood samples were obtained for measurements of plasma osmolality and AVT levels, and the hypothalamus was collected for extraction of total cellular RNA. A 519-bp AVT cDNA was prepared by reverse transcriptase-polymerase chain reaction and a 209-bp PstI/EcoRI restriction fragment from the 3' region of the fowl AVT cDNA was used as a probe for Northern blot analysis. Plasma osmolality and AVT levels in dehydrated birds were about 30 and 350% greater, respectively, than those in normally hydrated controls. The quantity of hypothalamic AVT mRNA was 2. 3-fold greater in water-deprived birds compared to controls. The size of the hypothalamic AVT transcript was about 100-bp longer in the water-deprived birds. As determined by RNase H treatment in the presence and absence of oligo(dT)12-18, the increase in mean size of the AVT mRNA in dehydrated animals was due to a longer poly(A) tract. Our results indicate that osmotic stress up-regulates expression of the AVT gene and increases the accumulation of AVT mRNA in the hypothalamus. This accumulation may, in part, be due to lengthening of the AVT mRNA poly(A) tail which is a general mechanism associated with stabilization of vertebrate mRNAs.

Animals↗
PubMed2005

Effect of anti-NGF on ovarian expression of alpha1- and beta2-adrenoceptors, TrkA, p75NTR, and tyrosine hydroxylase in rats with steroid-induced polycystic ovaries.

Estradiol valerate (EV)-induced polycystic ovaries (PCO) in rats are associated with higher ovarian release and content of norepinephrine, decreased beta2-adrenoceptors (ARs), and dysregulated expression of alpha1-AR subtypes, all preceded by an increase in the production of ovarian NGF. The aim of this study was to further elucidate the role of NGF in the ovaries by blocking the action of NGF during development of EV-induced PCO in rats. Control and EV-injected rats were treated with intraperitoneal injections of IgG (control and PCO groups) or with anti-NGF antibodies (anti-NGF and PCO anti-NGF groups) every third day for 5 wk starting from the day of PCO induction. Rat weight, estrous cyclicity, ovarian morphology, ovarian mRNA, and protein expression of alpha1-AR subtypes, beta2-AR, the NGF receptor tyrosine kinase A (TrkA), p75 neurotrophin receptor (p75NTR), and tyrosine hydroxylase (TH) were analyzed. Ovaries in both PCO and PCO anti-NGF groups decreased in size as well as in number and size of corpora lutea. mRNA expression of alpha1a-AR and TrkA in the ovaries was lower, whereas expression of alpha1b- and alpha1d-AR and TH was higher, in the PCO group than in controls. Protein quantities of alpha1-ARs, TrkA, p75NTR, and TH were higher in the PCO group compared with controls, whereas the protein content of beta2-AR was lower. Anti-NGF treatment in the PCO group restored all changes in mRNA and protein content, except that of alpha1b-AR and TrkA mRNAs, to control levels. The results indicate that the NGF/NGF receptor system plays a role in the pathogenesis of EV-induced PCO in rats.

Animals↗
PubMed2003

[Regulation of electrokinetic properties of human blood erythrocytes following exposure to emotional stressor].

Using the factor analysis, we studied the influence of psychoemotional strain, experienced by students under taking examinations, on the electrophoretic mobility of their erythrocytes. Under stress condition, redistribution of shares of cells with different mobility occurs, directed to the maintenance of the optimal value of the index average level in the total pool of erythrocytes of an individual. Under stress, five factors, taken in different combinations, participate in the control of erythrokinetic properties: those of restriction of cell accumulation with abnormal mobility, and of the population quantity heterogeneity control, in addition to factors of total functional condition, emotional tension, and individual psychological steadiness of students before examination. The expression and character of stress influence on the state of erythrocyte population depend on the intensity of the functional load of the organism.

Cell Movement↗
PubMed2001

Quantitative contributions of gluconeogenesis to glucose production during fasting in type 2 diabetes mellitus.

Contributions of gluconeogenesis to glucose production were determined between 14 to 22 hours into a fast in type 2 diabetics (n = 9) and age-weight-matched controls (n = 7); ages, 60.4 +/- 2.3 versus 55.6 +/- 1.2 years and body mass indices (BMI) 28.6 +/- 2.3 versus 26.6 +/- 0.8 kg/m2. Production was measured using a primed-continuous [6,6-2H2]glucose infusion and gluconeogenesis from 2H enrichment at carbons 2 and 5 of blood glucose on 2H2O ingestion. Plasma glucose concentration declined from 9.6 +/- 0.6 at 14 hours to 7.3 +/- 0.6 at 22 hours in the diabetics (P = .001) and from 5.4 +/- 0.1 to 5.0 +/- 0.1 in the controls (P < .05). Production from the 17th to 22nd hour declined 27.1% +/- 0.6% in the diabetics versus 18.5% +/- 0.8% in the controls (P = .001); from 10.4 +/- 0.3 to 7.6 +/- 0.2 versus 10.0 +/- 0.4 to 8.2 +/- 0.4 micromol/kg/min. Percent contributions of gluconeogenesis to production measured at 1 1/2 to 2-hour intervals beginning the 15th hour were 6.8% +/- 1.0% more in the diabetics than controls. The quantity of glucose contributed by gluconeogenesis declined 19.8% +/- 3.8% (P < .001) in the diabetics and 6.9% +/- 2.3% in the controls (P = .05); 7.21 +/- 0.32 to 5.74 +/- 0.26 versus 6.20 +/- 0.28 to 5.75 +/- 0.24 micromol/kg/min. The contribution of glycogenolysis to production, estimated from the difference between production and gluconeogenesis, declined to the same extent in diabetic and control subjects, 40.7% +/- 6.6% and 37.7% +/- 4.1%; from 3.23 +/- 0.35 to 1.86 +/- 0.26 versus 3.81 +/- 0.22 to 2.42 +/- 0.28 micromol/kg/min. Thus, gluconeogenesis contributed more to glucose production in the diabetic than control subjects. Production and the contribution of gluconeogenesis declined more in the diabetic subjects during the fast. The factors regulating these changes remain uncertain.

Deuterium↗
PubMed2000

Quantitative analysis of bowel gas using plain abdominal radiograph in patients with irritable bowel syndrome.

OBJECTIVE: Ideally, the diagnosis of irritable bowel syndrome (IBS) would be achieved using a minimal number of procedures. It is presumed that bowel gas is related to IBS, and it is easily visualized by plain abdominal radiograph. In the present study, to clarify the relationship between IBS and the quantity of bowel gas, the measured bowel gas volume using plain abdominal radiographs was compared with the pathology of IBS. METHODS: Plain abdominal radiographs were digitized and transmitted to a computer (computed radiography) in 30 IBS patients and 30 normal controls. The quantity of bowel gas, determined as the pixel value on images and standardized by physique, was defined as the gas volume score (GVS). Using the mean +/- 2SD of GVS in the control group as the normal score, IBS patients were divided into three groups: high, normal, and low. To examine the sequential reproducibility of a similar quantity of bowel gas, a second plain abdominal radiography was performed about 2 months later, and the GVS were compared. The colonic transit time was determined using radiopaque markers. RESULTS: There was a strong correlation between the quantities of bowel gas measured by two independent gastroenterologists. The mean GVS of IBS patients was significantly higher than that in the control group (p < 0.001). The sequential reproducibility was recognized in all 10 IBS patients. There was no significance between colonic transit time and GVS, nor between symptoms and GVS. CONCLUSIONS: Abdominal gas was analyzed objectively by using GVS, and GVS was considered to represent a useful tool for the diagnosis of IBS.

Adult↗
PubMed1992

Use of coculture of colonic mucosal biopsies to investigate the release of eicosanoids by inflamed and uninflamed mucosa from patients with inflammatory bowel disease.

Eicosanoid production was measured in cultured biopsies of colonic mucosa from control patients, with the irritable bowel syndrome, and from patients with proctosigmoiditis and with colonic Crohn's disease. Cultured inflamed colonic mucosa from patients with proctosigmoiditis and Crohn's disease produced more prostaglandin E2 and leukotrienes C4 than control tissues. In addition, eicosanoid production by macroscopically uninflamed or 'quiescent' mucosa from the right colon was examined in patients with proctosigmoiditis and between skip lesions in Crohn's disease patients. In the proctosigmoiditis group quiescent mucosa produced eicosanoids in similar quantities to control tissue. Coculture of quiescent plus inflamed tissue however, generated a marked increase in eicosanoid output in 12 of 20 of the patients and this was similar to the quantity obtained from two pieces of inflamed tissue. In the Crohn's disease group, quiescent mucosa produced more eicosanoids than control mucosa but production was markedly stimulated by coculture with inflamed mucosa in all patients. These findings suggest that in some patients with proctosigmoiditis and in all patients with Crohn's disease quiescent mucosa appears to be sensitised. A small but significant increase in the macrophage population may be partly responsible but it is likely that these and other cells are primed to release eicosanoids, and may be induced to do so by soluble mediators produced by actively inflamed tissue.

Adult↗
PubMed1998

Cell culture bags allow a large extent of ex vivo expansion of LTC-IC and functional mature cells which can subsequently be frozen: interest for a large-scale clinical applications.

The aim of this study was to evaluate the ex vivo expansion of normal CD34+ cells in gas-permeable polypropylene bags suitable for clinical use. Cells were cultured for 14 days in serum-free medium supplemented with SCF, IL3, IL6, FLT3-1, G-CSF + MGDF or Epo. The bags supported the expansion of hematopoietic cells in a similar manner to small scale well or flask systems, allowing mean expansions of up to 2193-fold for total nucleated cells, 140-fold for CFU-GM and 66-fold for LTC-IC. Increasing the initial cell concentration from 5 x 10(3) to 1 x 10(5)CD34+ cells/ml induced the production of granulocytic cells with terminal differentiation while simultaneously decreasing the overall extent of expansion of the white blood cells produced. We tested the phagocytic activity and oxidative metabolism of the white blood cells produced. The percentage of phagocytic cells was 39+/-0.5% in expanded cultures derived from fractions initiated at 5 x 10(3), 10(4) or 10(5) cells/ml and 45+/-6% in cultured cells obtained from starting fractions containing 5 x 10(4) cells/ml, as compared to 58+/-4% in normal controls. A study of the potential for oxygen-dependent microbe killing showed that the expanded cells produced H2O2, although in lesser quantities than control cells. We subsequently investigated the possibility of freezing expanded cells. Total cell recovery after thawing was 45+/-4%, while recoveries of progenitors and stem cells ranged from 65 to 90%, without any influence of the initial cell concentration. This new approach could be of major interest for clinical practice, as it would allow evaluation of the quality of a graft prior to its infusion and employs experimental conditions which meet the criteria for potential clinical use.

Blood Preservation↗
PubMed2000

Towards a control model for the highly cybernetic farming ecosystems.

A dynamic model based on the linear systems theory is developed in designing a highly cybernetic farming strategy to efficiently manage residuals generated in farm ecosystems. A linear cybemetic model would be used to describe the dynamic behavior of resource flow in the farm ecosystem in which the state variables are resource quantities, and the control variables are residual quantities. The controlled process is defined as the controlled management strategy change. Cybemetic mechanism shows the application of residuals as control measures have determinate effects on the controlled process as along as the farming system is observable and controllable in the control sense. To illustrate the model algorithm the idea is applied to simulate the dynamic response of residual phosphorus concentrations in an integrated pig/corn farming system located in the south Taiwan region. General results show that the residual phosphorous concentration is influenced by farming activities which are controlled by a system of gross input and net output parameters. This paper demonstrates using input-output analysis technique that residuals generated in the farming system is the most important cybemetic variable,

Agriculture↗