Interactions between prostaglandins and calcium: the importance of bell-shaped dose-response curves

Biological responses to PGs show two basic forms of dose/response relationship, plateau and bell-types. Although bell-shaped dose/response curves are well documented their possible occurrence is almost always ignored in the design and interpretation of experiments on PGs and related substances. This may lead to serious errors, several types of which are described. The ignoring of a well-documented phenomenon may take place because there is no accepted hypothesis which attempts to explain the bell-type curves. A hypothesis is proposed which accounts for both plateau and bell type responses. It is developed primarily with respect to PG-calcium interactions but may be applicable to some PG-cyclic nucleotide interactions as well. The model leads to precise predictions which can be experimentally tested in many systems.     

Effect of negative pi mesons on vascular permeability of brain in neonatal rats

Summary Neonatal rats and their radiation-induced cerebral petechial hemorrhages were used as an experimental system for evaluating the effects of negative pions on healthy tissue and especially on the microvasculature. Dose response curves for peak and plateau pions (dose range 150–250 rad and 100–400 rad, respectively) were obtained and compared with those of 200 kV X-rays of corresponding dose rates. The RBE of the peak pions was 1.1, that of the plateau pions 0.6 resulting in a peak/plateau ratio of 1.8. Implications were made as to the importance of this favorable peak/plateau relationship since the response of the capillary endothelium to pion-irradiation might be one of the limiting factors in radiotherapy.     

Pancreatic secretion in rats treated with intra-aortic prostaglandin E1

The effects from one dose of PGE1 on the endocrine pancreatic secretions have been studied in rat. The dose is injected i.a. very near the pancreas in the abdominal aorta at the level of the caeliac artery. Glycemia, insulinemia and glucagonemia are studied after i.v. glucose injection in: a) normal rats; b) rats free from their endogenous rate of PGs by previous treatment with indomethacin i.p. and c) with an excessive rate of PGE1. The treatment with PGE1 produces an inhibitory effect on the insulinic response to glucose, as well as hyperglycemia and hyperglucagonemia. In the cases without the endogenous rat of PGs the insulinic secretion as a response to glucose is greatly improved.     

The influence of xanthines on the contractile responses of PGF2 alpha and PGD2 in human parenchymal strips

Prostaglandins (PGs) F2 alpha and D2 are bronchoconstrictor agents which are released under allergic conditions such as asthma. The efficacy and potency of PGF2 alpha and PGD2 differ in some tissues. We compared the effects of these two PGs in sensitized human parenchymal strips. In six experiments, PGF2 alpha 0.1 and 0.3 microM produced greater contractions than PGD2 at the same concentrations. There were no significant differences between the contractions from the two PGs at concentrations of 0.01, 0.03, 1.0-10 microM and the two PGs appeared to be equipotent. We studied the effects of the anti-asthmatic drug theophylline, and its analogue enprofylline, on the contraction caused by these PGs. Theophylline 100 microM caused no change to the cumulative concentration response curves. However, enprofylline 100 microM reduced the PGF2 alpha-induced contractions.     

Analytical theory for the fluence,planar fluence,energy fluence,planar energy fluence and absorbed dose of primary particles and their fragments in broad therapeutic light ion beams

The purpose of the present work is to develop analytical expressions for the depth variation of the fluence, planar fluence, the energy fluence, planar energy fluence, the mean energy and absorbed dose of primary ions and their associated fragments in tissue-like media with ranges of clinical interest. The analytical expressions of the primary ions and associated fragments take into account nuclear interactions, energy losses, range straggling and multiple scattering. The analytical models of the radiation field quantities were compared with the results of the modified Monte Carlo (MC) code SHIELD-HIT₊. The results show that the shape of the depth absorbed dose distribution of the primary particles is characterized by an increasingly steep exponential fluence decrease with depth as the charge and atomic weight increase. This is accompanied by a compensating increased energy loss towards the Bragg peak as the charge of the ion increases. These largely compensating mechanisms are the main reason that the depth absorbed dose curve of all light ions is surprisingly similar. In addition, a rather uniform dose in the plateau region is obtained since the increasing fragment production almost precisely compensates the loss of primaries. The dominating light fragments such as protons and alpha particles are characterized by longer ranges than the primaries and their depth dose curves to some extent coincide well with the depth fluence curves due to a rather slow variation of mean stopping powers. In contrast, the heavier fragments are characterized by the build up of a slowing down spectrum similar to that of the primaries but with initially slightly shorter or longer ranges depending on their mass to atomic number ratio. The presented analytical theory for the light ion penetration in matter agree quite well with the MC and experimental data and may be very useful for fast analytical calculations of quantities like mean energy, fluence, energy fluence, absorbed dose, and LET.     

Concepts of threshold in mutagenesis and carcinogenesis

Although the existence of a threshold in the dose effect relationship is well documented for many, if not most, types of toxicological effects the existence of a threshold for the mutagenic effects of ionising radiation and of certain chemicals has been questioned since the middle of the century and only recently the question of thresholds for radiation and chemical carcinogenesis has been addressed. The essential facts for the interpretation of threshold dose–response curves are common to all type of effects and are: (i) the number and the identity of the target; (ii) the type and sensitivity of the endpoint used to quantify the effect. We therefore will first try to model the type of interactions which may be expected between a mutagen and its target and define from this whether a threshold dose-effect can be expected; in a second step the concept will be extended to heritable mutations and carcinogenesis.     

Study of the interaction between plasma proteoglycans and LDL by means of fluorescence spectroscopy]

The relevance of the interaction between LDL and PGs in the development of atherosclerotic processes is well known. However, the exact nature of the interaction and the consequent structural and/or conformational modifications of the lipoprotein remain to be clarified. It has been demonstrated that after this interaction the LDL particle is not recognized by specific cellular receptors and enters the scavenger pathway operating in different cell types. These effects have been shown by using aortic PGs, but PGs are also present in the plasma compartment and may interact constantly with LDL, taking part in the regulation of lipid metabolism. In order to assess the capability of plasma PGs to induce LDL modifications, we investigated their interactions by studying the changes in the organizational parameters of LDL by fluorescence spectroscopy. Plasma PGs were isolated by DEAE Sephacel ion exchange chromatography and Sephacryl S300 gel filtration in two different families: a low-charge PG and a high-charge PG. Human LDL was prepared from plasma of normolipemic donors by ultracentrifugal flotation between 1.025-1.045 g/ml. Steady-state anisotropy measures were obtained by analyzing the rotational diffusion rate of DPH after incubation of LDL with plasma PGs in a physiological ratio. In our experimental conditions, LDL incubation with plasma low-charge PG did not modify DPH fluorescence anisotropy, whereas LDL treatment with highly charged PGs induced a marked decrease of this parameter, suggesting a significant effect on LDL microviscosity. The data show that both the charge and the GAG composition of PGs appear to be critical factors in LDL-PG interaction.(ABSTRACT TRUNCATED AT 250 WORDS)     

Proteoglycan control of cell movement during wound healing and cancer spreading.

By virtue of their multifunctional nature, proteoglycans (PGs) are thought to govern the process of cell movement in numerous physiological and pathological contexts, spanning from early embryonic development to tumour invasion and metastasis. The precise mode by which they influence this process is still fragmentary, but evidence is accruing that they may affect it in a multifaceted manner. PGs bound to the plasma membrane mediate the polyvalent interaction of the cell with matrix constituents and with molecules of the neighbouring cells' surfaces; they modulate the activity of receptors implicated in the recognition of these components; and they participate in the perception and convergence of growth- and motility-promoting cues contributed by soluble factors. Through some of these interactions several PGs transduce to pro-motile cells crucial intracellular signals that are likely to be essential for their mobility. A regulated shedding of certain membrane-intercalated PGs seems to provide an additional level of control of cell movement. Coincidentally, matrix-associated PGs may govern cell migration by structuring permissive and non-permissive migratory paths and, when directly secreted by the moving cells, may alternatively create favourable or hostile microenvironments. To exert this latter, indirect effect on cell movement, matrix PGs strongly rely upon their primary molecular partners, such as hyaluronan, link proteins, tenascins, collagens and low-affinity cell surface receptors, whereas a further finer control is provided by a highly regulated proteolytic processing of the PGs accounted by both the migrating cells themselves and cells of their surrounding tissues. Overall, PGs seem to play an important role in determining the migratory phenotype of a cell by initiating, directing and terminating cell movement in a spatio-temporally controlled fashion. This implies that the "anti-adhesive and/or "anti-migratory" properties that have previously been assigned to certain PGs may be re-interpreted as being a means by which these macromolecules elaborate haptotaxis-like mechanisms imposing directionality upon the moving cells. Since these conditions would allow cells to be led to given tissue locations and become immobilized at these sites, a primary function may be ascribed to PGs in the dictation of a "stop or go" choice of the migrating cells.     

Desferrioxamine, an iron chelator, upregulates cyclooxygenase-2 expression and prostaglandin production in a human macrophage cell line

Prostaglandins (PGs) play regulatory roles in a variety of physiological and pathological processes, including the immune response, cytoprotection and inflammation. Desferrioxamine (DFX), an iron chelator, is known to reduce free radical-mediated cell injury and to upregulate certain inflammatory mediators. We investigated the effects of DFX on the production of PGs and the expression of cyclooxygenase-2 (COX-2), the rate-limiting enzyme in the synthesis of PGs, using a human macrophage cell line, U937. Our results showed that COX-2 expression and PGE(2) production are upregulated by DFX treatment and that this upregulation is dependent on both COX-2 promoter activity and alteration of mRNA stability. COX-2 promoter activity may be, at least in part, mediated by activation of the extracellular signal-regulated kinase pathway. These findings suggest that iron metabolism may regulate inflammatory processes by modulating PGs as well as other inflammatory mediators.     

Ecdysteroidogenic action of Bombyx prothoracicotropic hormone and bombyxin on the prothoracic glands of Rhodnius prolixus in vitro

An in-vitro assay for ecdysteroid synthesis by the prothoracic glands (PGs) of fifth instar Rhodnius prolixus has been employed to evaluate the actions of prothoracicotropic neuropeptides from the silkmoth, Bombyx mori. Crude prothoracicotropic hormone (PTTH) extracts of recently emerged adult brain complexes of Bombyx induced a dose-dependent stimulation of ecdysteroid synthesis by Rhodnius PGs, which was similar to that obtained using crude Rhodnius PTTH. In both cases, maximum stimulation was obtained with one brain equivalent. Rhodnius PGs were then challenged with incremental doses of recombinant Bombyx PTTH and synthetic bombyxin-II. Dose-response curves for the action of both peptides on Rhodnius PGs were very similar to those obtained for their action on the pupal PGs of Bombyx in vitro. Bombyx PTTH stimulated the PGs of Rhodnius at concentrations comparable to those effective on Bombyx. The curve for Bombyx PTTH showed a steep ascending region from 3 to 8ng/ml and a sharp peak. For bombyxin, concentrations 40-fold higher were required to elicit the same amount of stimulation as obtained using Bombyx PTTH. Therefore, Rhodnius PGs possess recognition sites for both Bombyx PTTH and bombyxin. This is the first study of the ecdysteroidogenic properties of the Bombyx peptides on a heterologous species. It is suggested that the function and conformation of PTTH may be conserved between distantly related insect groups.     

Complex type of kinetics of fructose-1,6-diphosphate from the rat and rabbit liver

Studies on rat and rabbit liver fructose 1.6-bisphosphatase inhibition by AMP showed that with an increase in EDTA concentration the hyperbolic AMP inhibition curve is transformed into a sigmoidal one. At intermediate EDTA concentrations, the kinetic curves have a plateau. The appearance of the intermediate plateau may be due to the superposition of kinetic curves corresponding to two enzyme forms simultaneously present in the assay mixture. One of these forms deprived of endogenous Me2+ (presumably Zn2+) is inhibited by AMP in a cooperative manner, while the other one retains Me2+ which prevents the cooperative response of the enzyme to AMP.     

Effect of piracetam, a nootropic agent, on rat brain monoamines and prostaglandins

Piracetam is the prototype of a new class of psychotropic drugs, the nootropic agents, which are claimed to selectively improve the higher telencephalic integrative activities. The effect of piracetam on rat brain monoamines and prostaglandins (PGs) was assessed so as to garner information on its mode of action. Two doses of the drug were used, a lower dose (20 mg/kg ip) and a higher dose (100 mg/kg, ip), the latter being known to exert a facilitatory effect on learning and memory. Piracetam produced a dose-related effect on rat brain serotonin (5HT) and noradrenaline (NA), with the lower dose inducing a decrease in 5HT levels and an increase in NA concentrations. The higher dose of piracetam produced the opposite effect. Dopamine (DA) levels were not significantly affected. The lower dose of the drug attenuated 5HT turnover and augmented that of NA, whereas the higher dose of piracetam produced the reverse effects, in clorgyline treated rats. The lower dose of piracetam produced a slight and statistically insignificant increase in rat brain PGE2 and PGF2 alpha. However, the higher dose of the drug produced marked increase in the levels of both the PGs. The observed biochemical effects may provide a basis for the nootropic effect of piracetam. However, they may also be due to the GA-BA-mimetic action of the drug, particularly those observed with the lower dose of piracetam.     

Plasmatocyte-spreading peptide influences hemocyte behavior via eicosanoids

Hemocyte-spreading behavior is required for expressing a cellular immune response, nodulation, which clears the vast majority of invading microbes from circulation. The nodulation response is completed by a layer of plasmatocytes, which spread over the nodule and initiate a malanization process leading to darkened nodules. Plasmatocyte-spreading peptide (PSP), the first reported insect cytokine, is responsible for mediating the spreading and attachment of some subclasses of plasmatocytes to nodules. Prostaglandins (PGs), one group of eicosanoids formed from arachidonic acid (AA), also mediate plasmatocyte spreading (PS), although the potential interactions between the PSP and PG signal transduction pathways have not been investigated. We tested our hypothesis that PSP acts via biosynthesis of eicosanoids, specifically PGs, in the beet armyworm, Spodoptera exigua. In this study, we report that (1) PSP and PGE(2) independently stimulated Ca(++)-dependent PS, (2) inhibitors of PG biosynthesis reversibly blocked PS, (3) dsRNA silencing the gene encoding proPSP blocked PS, which was rescued by PSP and by AA, (4) PSP-stimulated PS was reversibly impaired by inhibitors of PG biosynthesis, and (5) the inhibitor-impaired spreading was rescued by AA. Taken together, these points strongly support our model showing that PSP acts via a plasmatocyte-surface receptor, which stimulates biosynthesis of the PGs responsible for mediating plasmatocytes spreading.     

Prostaglandins Stimulate Serotonin Acetylation in Chick Pineal Cells: Involvement of Cyclic AMP-Dependent and Calcium/Calmodulin-Dependent Mechanisms

Abstract: The effects of prostaglandins (PGs) on the activity of the rate-limiting enzyme of melatonin biosynthesis, aryl-alkylamine- N -acetyltransferase (NAT) were investigated on primary cultures of dispersed chick pineal cells. In indomethacin-treated cells, PGs caused a four-fold increase in NAT activity. This response was associated with an eightfold increase in cyclic AMP (cAMP) levels. The potency order of PGs was the same for NAT and for cAMP responses (PGE¹ > PGE² > PGF^2α≫ cloprostenol). However, each PG tested was 30- to 200-fold more potent to increase NAT activity than to stimulate cAMP accumulation. As a result, half-maximal stimulation of NAT by PGs was not associated with an increase in cAMP levels. Half-maximal stimulation of NAT by PGE¹ was highly sensitive to inhibition by a calcium/calmodulin antagonist (W-7). In contrast, maximal stimulation of NAT by PGE¹ as well as stimulations evoked by either forskolin or 8-bromo-cAMP were poorly sensitive to inhibition by W-7. These results indicate that an increase in cAMP levels may be responsible for the maximal stimulation of NAT evoked by PGs, whereas half-maximal stimulation of NAT by PGs would rely principally on a calcium/calmodulin-dependent mechanism.     

Vascular reactivity in hypertensive rats after treatment with anti-hypertensive agents

Isolated perfused mesenteric arteries obtained from experimental hypertensive rats (spontaneous and deoxycorticosterone/NaCl) exhibit an increased vascular reactivity to noradrenaline and 5-hydroxytryptamine. The dose response curves obtained exhibited in the threshold dose. After 4 weeks of antihypertensive therapy (a combination of hydrallazine, hydrochlorothiazide and reserpine) which lowered the blood pressures of hypertensive rats to normotensive levels the arteries from the hypertensive animals still exhibited an increased reactivity to vasoconstrictor agents. These results support the hypothesis that the increased reactivity observed in hypertensive animals may be partially due to adaptive structural changes in the blood vessels. However, the persistence of the hyperactivity after antihypertensive therapy seriously questions its involvement in the maintenance of the elevated blood pressure.     

Indomethacin impairs LPS-induced behavioral fever in toads.

We tested the hypothesis that PGs mediate lipopolysaccharide (LPS)-induced behavioral fever in the toad Bufo paracnemis. Measurements of preferred body temperature (T(b)) were performed with a thermal gradient. Toads were injected intraperitoneally with the cyclooxygenase inhibitor indomethacin (5 mg/kg), which inhibits PG biosynthesis, or its vehicle (Tris) followed 30 min later by LPS (0.2 and 2 mg/kg) into the lymph sac. LPS at the dose of 0.2 mg/kg caused a significant increase in T(b) from 7 to 10 h after injection, and then T(b) returned toward baseline values. LPS at the dose of 2 mg/kg produced a different pattern of response, with a longer latency to the onset of fever (10th h) and a longer duration (until the end of the experiment at the 15th h). Tris significantly attenuated the fever induced by LPS at 0.2 mg/kg, but not at 2 mg/kg. Moreover, indomethacin completely blocked the fever evoked by LPS (2 mg/kg). These results indicate that the behavioral fever induced by LPS in toads requires the activation of the COX pathway, suggesting that the involvement of PG in fever has an ancient phylogenetic history and that endogenous PGs raise the thermoregulatory set point to produce fever, because behavioral thermoregulation seems to be related to changes in the thermoregulatory set point.     

Mesenchymal stem cells,neural lineage potential,heparan sulfate proteoglycans and the matrix

Along with the tri-lineage of bone, cartilage and fat, human mesenchymal stem cells (hMSCs) retain neural lineage potential. Multiple factors have been described that influence lineage fate of hMSCs including the extracellular microenvironment or niche. The niche includes the extracellular matrix (ECM) providing structural composition, as well as other associated proteins and growth factors, which collectively influence hMSC stemness and lineage specification. As such, lineage specific differentiation of MSCs is mediated through interactions including cell–cell and cell–matrix, as well as through specific signalling pathways triggering downstream events. Proteoglycans (PGs) are ubiquitous within this microenvironment and can be localised to the cell surface or embedded within the ECM. In addition, the heparan sulfate (HS) and chondroitin sulfate (CS) families of PGs interact directly with a number of growth factors, signalling pathways and ECM components including FGFs, Wnts and fibronectin. With evidence supporting a role for HSPGs and CSPGs in the specification of hMSCs down the osteogenic, chondrogenic and adipogenic lineages, along with the localisation of PGs in development and regeneration, it is conceivable that these important proteins may also play a role in the differentiation of hMSCs toward the neuronal lineage. Here we summarise the current literature and highlight the potential for HSPG directed neural lineage fate specification in hMSCs, which may provide a new model for brain damage repair.     

Tracing personalized health curves during infections

It is difficult to describe host-microbe interactions in a manner that deals well with both pathogens and mutualists. Perhaps a way can be found using an ecological definition of tolerance, where tolerance is defined as the dose response curve of health versus parasite load. To plot tolerance, individual infections are summarized by reporting the maximum parasite load and the minimum health for a population of infected individuals and the slope of the resulting curve defines the tolerance of the population. We can borrow this method of plotting health versus microbe load in a population and make it apply to individuals; instead of plotting just one point that summarizes an infection in an individual, we can plot the values at many time points over the course of an infection for one individual. This produces curves that trace the course of an infection through phase space rather than over a more typical timeline. These curves highlight relationships like recovery and point out bifurcations that are difficult to visualize with standard plotting techniques. Only nine archetypical curves are needed to describe most pathogenic and mutualistic host-microbe interactions. The technique holds promise as both a qualitative and quantitative approach to dissect host-microbe interactions of all kinds.     

AN INTERPRETATION OF DOSE-RESPONSE CURVES FOR LIGHT-INDUCED CELL ELONGATION IN FERN PROTONEMATA

Protonemata of Onoclea sensibilis and Diyopteris filix-mas elongate in response to both red and far-red light. The promotion caused by far-red is larger than that caused by red light. This phenomenon differs from a typical response to phytochrome, the photoreceptor pigment immediately suggested by the activity of red and far-red light. The phenomenon has been explained by two different hypotheses, one of which holds that phytochrome is solely responsible for the response, whereas the other postulates an interaction between phytochrome and P₅₈₀, a yellow-green light absorbing pigment, to account for the response. The hypothesis that phytochrome is the sole photoreceptor leads to some specific predictions concerning the shapes of the dose-response curves for light-induced protonema elongation. These predictions were tested with both continuous and short-term irradiation. In all instances saturating far-red light caused greater elongation than did saturating red light, and no dose of red light duplicated the activity of saturating far-red light. Other experiments tested the interactions of red and far-red light and the effects of different doses of yellow-green light on protonema elongation. The results of many of the experiments were not in agreement with the hypothesis that phytochrome is the sole photoreceptor, whereas they were in agreement with the assumption that filament elongation is controlled by both phytochrome and P₅₈₀.     

Diffusion and Quasi-diffusion Resistances in Relation to the Carboxylation Kinetics of Maize Leaves

A “quasi-diffusion resistance”, rq, is defined to accommodate the role which the thermochemical and photochemical phenomena of photosynthesis play in the control of CO2 fixation to the terminology and approach of the diffusion resistance analogue for the CO2 exchange of leaves. The relationship of rq to Rabinowitch's classical rectangular hyperbolic model of photosynthesis rate as a function of CO2 concen-tration at the carboxylating surface is discussed. Examination of Kmapp for phos-phopyruvate carboxylase (the predominant carboxylase in maize) suggests, as a reasonable hypothesis for light-saturated maize leaves, that rq may be essentially independent of ambient CO2-concentration up to at least 300 μ1/l. A corollary of the hypothesis is that an increase of diffusion resistance, rather than of rq, may account for the observed curvature of the response curves of light-saturated maize leaf photosynthesis to ambient CO2-concentration. An experiment carried out on fieldgrown maize plants, using a well controlled leaf chamber as a nitrous oxide diffusion porometer, gave evidence which strongly supported the hypothesis.