Enhancement of intestinal immune function in mice by β-D-glucan from aureobasidium pullulans ADK-34

β-Glucans, glucose polymers that are the main constituents of the outer cell walls of micro-organisms such as fungi and yeast, are known to play an immunostimulatory role. We prepared β-glucan (β-(1-3),(1-6)-D-glucan) from an edible cultured fungus through fermentation techniques using a strain of Aureobasidium pullulans ADK-34. The purity of this β-glucan preparation (AP-FBG) was demonstrated to be high through various instrumental analyses. We then examined the effects of AP-FBG on intestinal immune systems. We prepared Peyer's patch (PP) cells and measured interleukin (IL)-5, IL-6, and IgA production in culture media with AP-FBG. We found that both cytokines and IgA increased; furthermore, IL-6 secreted by PP dendritic cells (PPDCs) cultured in the presence of AP-FBG significantly increased. We tested IgA production after oral administration of AP-FBG for 2 weeks and found that AP-FBG tended to promote the production of IgA in the small intestine. Interestingly, we observed a significant increase in IgA production in the small intestines of mice treated with cyclophosphamide (CY; an immunosuppressant) after oral administration of AP-FBG diet compared with CY-treated and control diet mice. Production of IL-6 and IgA by PP cells and IL-6 production by PPDCs in AP-FBG-fed and CY-treated mice also increased. These results demonstrate that AP-FBG has the ability to activate PPDC and induce IL-6 production and IgA secretion in PP cells. These abilities were more clearly expressed when AP-FBG was orally administered in a CY-induced immunosuppressed condition. Therefore, AP-FBG may be a useful ingredient for preparing functional foods with immunomodulatory activities.

[Effect of oral administration of β-D-glucan from Aureobasidium pullulans ADK-34 on Candida and MRSA infections in immunosuppressed mice]

We examined the effect of the oral administration of β-D-glucan derived from Aureobasidium pullulans ADK-34 (AP-FBG) on Candida albicans or methicillin-resistant Staphylococcus aureus (MRSA) infection in immunosuppressed mice. Mice pretreated with cyclophosphamide (CY) were intraperitoneally administered AP-FBG for 4 days and then infected with 6×10(4) C. albicans cells. In a preliminary experiment, the survival time of the Candida-infected mice treated with AP-FBG was clearly prolonged. Similarly, the effect of the oral administration of AP-FBG was examined. Mice were orally given 2.5% AP-FBG in feed for 42 days from 14 days prior to 2×10(4) C. albicans cells infection. The survival time of mice treated with AP-FBG was significantly prolonged and the viable cell count in the kidneys of the survivors was significantly decreased at 30 days after infection. The effects of the oral administration of AP-FBG on intestinal MRSA infection were also examined. Mice were given 2.5% AP-FBG orally in feed for 30 days before and after oral MRSA infection and treated with CY 12 days after the infection. The number of viable MRSA cells or the IgA production in feces did not significantly change, while AP-FBG administration seemed to relieve temporally the loss of body weight of mice.

CONCLUSIONS

These results suggest that oral pre-administration of AP-FBG promoted resistance of CY-treated mice to C. albicans and lessened the weight reduction of CY-mice infected by MRSA.

Barley low molecular weight β-glucan potently induces maturation of mouse dendritic cells

BACKGROUND

Accumulating evidence indicates that non-toxic immunostimulants with strong differentiation/maturation-inducing activity for dendritic cells (DCs) might be useful for preventing or even curing cancer.

MATERIALS AND METHODS

Mouse bone marrow (BM) cells were cultured in the presence of various glucans and their differentiation/maturation-inducing activities were compared by measuring cytokines secreted in the culture medium.

RESULTS

Barley-derived β-glucan with an average molecular weight of 2 kDa (BBG-Low) remarkably stimulated the formation of mature DCs from immature mouse DCs. The amount of interleukin-6 produced by sequential treatment of BM cells with granulocyte-macrophage colony-stimulating factor and 10 μg/mL of BBG-Low was approximately 30 times higher than that obtained by a similar sequential treatment using barley β-glucan of 40-70 kDa instead of BBG-Low.

CONCLUSION

BBG-Low induces the formation of mature DCs from immature DCs and suggests that BBG-Low will be useful as a potent nontoxic immunostimulator.

Induction of IFN-γ by a highly branched 1,3-β-d-glucan from Aureobasidium pullulans in mouse-derived splenocytes via dectin-1-independent pathways

We have previously elucidated the precise structure of a unique type of 1,3-β-D-glucan, AP-FBG (Aureobasidium pullulans-fermented β-D-glucan), from the fungus A. pullulans and found that AP-FBG strongly induced the production of various cytokines in DBA/2 mouse-derived splenocytes in vitro. However, the mechanism(s) of action of AP-FBG on in vitro mouse primary cells have not been characterized in detail. Herein, we report that the production of IFN-γ in DBA/2 mouse-derived splenocytes by AP-FBG was not inhibited following treatment with an anti-dectin-1 neutralizing antibody. In addition, AP-FBG not only failed to activate dectin-1-mediated signaling pathways, examined by a reporter gene assay but also failed to bind to dectin-1, a pivotal receptor for 1,3-β-D-glucan. Taken together, AP-FBG induced cell activation via dectin-1-independent pathways.

Granulocyte macrophage colony-stimulating factor is required for cytokine induction by a highly 6-branched 1,3-β-D-glucan from Aureobasidium pullulans in mouse-derived splenocytes

We have previously obtained and elucidated the precise structure of a highly branched 1,3-β-D-glucan (with 6-monoglucopyranosyl side chains), Aureobasidium pullulans-fermented β-D-glucan (AP-FBG), from the fungus A. pullulans. However, the mechanism(s) of the effects of AP-FBG on in vitro mouse primary cells have not been analyzed in detail. Herein, we report that the induction of cytokines by AP-FBG was dependent on the existence of a granulocyte macrophage colony-stimulating factor (GM-CSF); this is similar way to be a typical 1,3-β-D-glucan from Sparassis crispa (SCG), which is a 1,3-β-D-glucopyranosyl backbone with single 1,6-β-D-glucopyranosyl side branching units every three residues. In other words, the production of cytokines in DBA/2-mouse-derived splenocytes by AP-FBG was completely hampered by an anti-GM-CSF neutralizing monoclonal antibody. Furthermore, the addition of exogenous GM-CSF to C57BL/6-derived splenocytes, which are less sensitive to AP-FBG, induced the production of cytokines by AP-FBG. Therefore, GM-CSF is indispensable for the induction of cytokines by AP-FBG in mouse-derived splenocytes. This finding has provided a new insight into our understanding of the actions of β-D-glucan but will also aid in the design and development of more effective β-D-glucan agents.

A highly branched 1,3-beta-D-glucan extracted from Aureobasidium pullulans induces cytokine production in DBA/2 mouse-derived splenocytes

We recently elucidated the structure of a highly branched 1,3-beta-D-glucan with 6-monoglucopyranosyl side chains, extracted from Aureobasidium pullulans (AP-FBG). Although the biological effects of beta-D-glucans are known to depend on their structures, the effects of a highly branched 1,3-beta-D-glucan on the production of cytokines by leukocytes in mice have not yet been elucidated. In this study, we found that AP-FBG strongly induced the production of various cytokines, especially Th1 cytokines (e.g., IFN-gamma and IL-12p70) and Th17 cytokines (e.g., IL-17A), but did not induce the production of IL-4, IL-10, and TNF-alpha in DBA/2 mouse-derived splenocytes in vitro.

Structural characterisation and biological activities of a unique type beta-D-glucan obtained from Aureobasidium pullulans

A beta-D-glucan obtained from Aureobasidium pullulans (AP-FBG) exhibits various biological activities: it exhibits antitumour and antiosteoporotic effects and prevents food allergies. An unambiguous structural characterisation of AP-FBG is still awaited. The biological effects of beta-D-glucan are known to depend on its primary structures, conformation, and molecular weight. Here, we elucidate the primary structure of AP-FBG by NMR spectroscopy, and evaluate its biological activities. Its structure was shown to comprise a mixture of a 1-3-beta-D-glucan backbone with single 1-6-beta-D-glucopyranosyl side-branching units every two residues (major structure) and a 1-3-beta-D-glucan backbone with single 1-6-beta-D-glucopyranosyl side-branching units every three residues (minor structure). Furthermore, this beta-D-glucan exhibited immunostimulatory effects such as the accumulation of immune cells and priming effects against enterobacterium. To our knowledge, 1-3-beta-glucans like AP-FBG with such a high number of 1-6-beta-glucopyranosyl side branching have a unique structure; nevertheless, many 1-3-beta-glucans were isolated from various sources, e.g. fungi, bacteria, and plants.

An Application of Percolation Theory to the Electrolyte Penetration through Porous Water-Swollen Cellulose Triacetate Membrane

Permeability coefficients P of KCl through porous cellulose triacetate (CTA) membranes were measured as a function of the water volume fraction V(W) and diffusion coefficients D were determined using solubility parameters K and a membrane thickness d from the relationship of P = KD/d. D increased with an increase in V(W). D especially increases abruptly around V(W) = 0.5, which corresponds to 2% triethylene glycol (TEG) content. The percolation theory was applied to the experimental results under the conditions D(A) = D (V(W) = 1) = 1.8 x 10(-5) cm(2) s(-1), D(B) = D(V(W) = 0) = 1.8 x 10(-8) cm(2) s(-1), coordination number (Z) = 2.5, 3, 3.5, and 4, and packing fraction f = 1.0. A good fit was obtained at Z = 3.5 because the experimental and calculated results also shifted at the same V(W) below V(W) = 0.5. It is suggested that a phase inversion, that is, change of a discontinuous water phase to a continuous water phase, occurs around V(W) = 0.5. Above V(W) = 0.5, the experimental results agree well with the calculated line for Z = 3 or Z = 2.5 which means that the coordination numbers decrease with an increase in water content. It is thought that V(W) is overestimated because it is hard to completely wipe off the excess water quickly from the membrane surface. Z = 3.5 means that a pore can connect in 3.5 directions. Copyright 1999 Academic Press.

Membrane Potential of Composite Bipolar Membrane in Ethanol-Water Solutions: The Role of the Membrane Interface

The membrane potential across a composite bipolar membrane (CBM) composed of a cation-exchange membrane with an anion-exchange membrane is theoretically and experimentally analyzed for LiCl ethanol-water solutions. The theoretical approach is based on an extension of the Donnan equilibrium and the Nernst-Planck equation of monopolar charged membranes for the case of two ion-exchange layers by considering the effect of electrolyte ion pairing in the external solution. The experimental results show that the effective membrane charge densities of the two ion-exchange layers will become smaller than those which are separately estimated for each layer. We have introduced a contact factor, zeta, into the theoretical approach to clarify this phenomenon in this study, and the theoretical predictions were in good agreement with the experimental data. The membrane potential measurements show that CBM has the characteristics of a bipolar membrane and can significantly contribute to a better electrochemical characterization of the CBMs. Copyright 1999 Academic Press.

Effect of the Interface Component on Current-voltage Curves of a Composite Bipolar Membrane for Water and Methanol Solutions

The current-voltage curves of a composite bipolar membrane (CBM) were experimentally measured by varying the interface component between cation- and anion-exchange membranes for water and methanol solutions. In each solution system, 0.05 mol/l LiCl was used as the electrolyte. The interface component was varied by pasting the polymers or installing the thin membranes in the intermediate region of the CBM. The measured results show that the functional groups of the polymers and thin membranes enhanced the water and methanol splitting effect. This phenomenon can be explained by the protonation-deprotonation reactions occurring between these functional groups and the water or methanol molecules in the intermediate region of the CBM. The effect of transition metal compounds existing in the intermediate region of the CBM was also experimentally examined in this study. It was found that the effect of transition metal compounds on water or methanol splitting was not obvious. Copyright 1999 Academic Press.

Hydrodynamic Surface Flow and the Swelling Effect of C2 and C4 Alkenes through Anhydrous Ag+-Doped Perfluorocarbon Type Ion-Exchange Membranes

The transport mechanism was investigated for n-butane, 1-butene, ethane, and ethene through anhydrous Ag+-doped PSM at various upstream gas pressures. 1-Butene and ethene molecules can be adsorbed and form multilayers on the Ag+ sites in the membrane. Their adsorption behavior can be described by the BET n-layer adsorption theory. These adsorbed alkene molecules can also swell the surrounding polymer chains to a certain extent, causing resistance to the migration of these alkene multilayer molecules to decrease as the concentration of the adsorbed alkenes increases. The permeation behavior of 1-butene and ethene is mainly controlled by the hydrodynamic surface flow mechanism, and their fluxes are much higher than those of alkanes, especially at high upstream gas pressures. This leads to the high ideal selectivity of 1-butene/n-butane and ethene/ethane at relatively high pressure. It is also shown that the more C atoms present in the hydrocarbon molecules, the higher will be the permselectivity of alkenes relative to their corresponding saturated alkanes, which will be expected in the anhydrous Ag+-doped PSM. Copyright 1999 Academic Press.

Ion Transport across a Polyelectrolyte-Adsorbed Cellulose Triacetate Membrane in the Multicomponent Ionic Systems

The effects of polyelectrolyte adsorption by cellulose triacetate (CTA) membrane on ionic transport are investigated in two systems: the three-ionic-component system and the multicomponent-ionic system. In the three-ionic-component system, the permeabilities of two anions are affected by the competitive ion. Especially in the case of the albumin-adsorbed CTA membrane, there exists much greater specificity for the permeability of SO2-4 than in the case of the lysozyme-adsorbed membrane. On the other hand, in the case of the PAS-H(10L)(polydiallyldimethylammonium chloride)-adsorbed membrane, the permeability coefficient of HPO2-4 increases, though there exists the effect of a competitive ion. In a multicomponent-ionic system, the logarithmic permeability coefficient ratios (rP) of each ion in an adsorbed membrane to that in a nonadsorbed membrane decreased by PAS-H(10L) adsorption for all cations. The rP of bivalent cations decreased more than those of univalent cations because of the rejection from the positively charged adsorbed layer. On the other hand, the permeabilities slightly increase because of the attraction from the PAS-H(10L)-adsorbed layer when competitive anions exist among them. Furthermore, the increase in the HPO2-4 permeability is confirmed by PAS-H(10L)-adsorption on a CTA membrane for a case very similar to the actual anion multicomponent system. These are the most important results in the application for an approach to phosphate extraction from blood across an artificial kidney membrane. Copyright 1999 Academic Press.

Effect of Fixed Charge Groups and Counter Ions on the Transport Phenomena of Paraffin and Olefin across Anhydrous Negatively Charged Membranes

Permeability coefficients, apparent diffusion coefficients, and apparent solubility coefficients of n-butane and 1-butene gases across anhydrous sulfonated and carboxylated polyperfluorocarbon-type cation exchange membranes which have different counterions of Na+, Ag+, Co2+, and Ni2+ were investigated at 25 degreesC. Prior to the n-butane and 1-butene gas permeability measurements, O2 gas permeabilities were measured. From the results, it was shown that those membranes appeared to dense membranes. In each membrane, the permeability of 1-butene was higher than that of n-butane. In comparison with the same counterion membranes, the sulfonated membrane had higher permeability than the carboxylated membrane for both gases. The Ag+-form sulfonated membrane exhibited the highest permeability coefficient for 1-butene and the ideal separation factor of 1-butene/n-butane was 10.3. This is caused by the high solubility of 1-butene gas. From the calculated result using the MO method, it was shown that the interaction between the olefin and metal ions was weakened by the influence of a charged group. Therefore, the affinity between the olefin and Co2+ or Ni2+ did not function in the membrane as expected because of the divalent ions. This is the reason why the solubility coefficients of Co2+- and Ni2+-form membranes were smaller than those of the Ag+-form membrane. Copyright 1998 Academic Press.

Effect of Interfacial Tension on the Formation of the Gradient Morphology in Polymer Blends

In order to investigate the effect of interfacial tension on the formation of gradient phase morphology in polymer blends, a saponification reaction was carried out in this study to obtain several kinds of EVA with different contents of -OH groups. These EVAs with different -OH contents, namely with different polarities, were then blended with PP, and thus a series of PP/EVA blends with different interfacial tensions was obtained. The same initial droplet size could be obtained for PP/EVA blends with different interfacial tensions during compounding through adjusting the degree of saponification of EVA. It was found that all these PP/EVA blends could form a gradient morphology in the vertical section of the samples as PP/EVAc blends. Using a computer image analyzer, the vertical distributions of the dispersed droplet size and the EVAc component in each blend were determined. The results showed that the EVA droplet size and the EVA component increased in the vicinity of the sample surface with increasing interfacial tension of the blends; i.e., the greater the interfacial tension between PP and EVA, the larger the gradient tendency in the blend. Copyright 1998 Academic Press.

Comparison of Surface and Net Charge Densities of Poly(acrylonitrile) Membranes Grafted with Ionic Monomers: Hydrophilic and Hydrophobic Effects of Graft Chain

The apparent surface charge densities of grafted poly(acrylonitrile) (PAN) membranes (determined by measurement of zeta potential) were compared with net charge densities (determined by potentiometric titration) in order to examine the effects of hydrophilic and hydrophobic graft chains at the pore surface. Membranes with hydrophilic graft chains showed much smaller net charge densities than membranes with hydrophobic graft chains. However, the apparent surface charge densities of the membranes with hydrophilic graft chains were much larger than those of the membranes with hydrophobic graft chains. This fact can be explained by the formation of ion pairs between charge groups and counterions. Dissociation behaviors for the two types of membranes, in which electrostatic interactions of the charge groups play a significant role were distinctly different. These results confirm the occurrence of ion-pairing effects between the charge groups and the counterions for hydrophobic graft chains in which dissociation of some of the charge groups is suppressed. Copyright 1998 Academic Press.

Sorption Isotherms of Gases by Polymer Membranes in the Glassy State: An Explanation Based on the Nonequilibrium Thermodynamics

Sorption isotherms of glassy polymers are concave to the pressure axis, and the absolute sorption levels are almost an order of magnitude higher than that of rubbery polymers on the relatively low-pressure side. There are several models to interpret this behavior, and the dual sorption model is the most widely accepted one among them. In the present work, sorption isotherms were first derived from permeation data with several gases for four polymer membranes which might be representative of the dual sorption model: two of them were in a glassy state (cellulose acetate and polyamide), the third one was a block copolymer which was composed of a glassy polymer and a rubbery polymer at the measuring temperature, and the fourth one was a Nafion membrane which was taken as a model membrane because of its channel structure with adsorption sites of charged groups supported by a rubbery polymer. These results did not necessarily support the dual sorption model. Subsequently, the validity of the underlying assumptions of two other sorption models for glassy polymers, that is, the matrix model and the deformation model, were examined and a new equation for the sorption isotherm with an ordering parameter was derived, which implied that the glassy polymer was in a nonequilibrium state and changed from the glassy to the rubbery state by absorbing the gas. Copyright 1998 Academic Press.

Interfacial State Change of Cellulose Triacetate Membrane by Adsorption of Polyelectrolyte

Lysozyme, albumin, and PAS-H (poly diallyl dimethyl ammonium chloride), which are positively and negatively charged proteins, and cationic polysulfones, respectively, were adsorbed by a cellulose triacetate (CTA) membrane to investigate their effects on ionic transport through the membrane. The interface states between the membrane and the adsorption layer are discussed based on the measurements of contact angle and membrane potential and atomic force microscopy (AFM). The contact angle shows that the membrane changed from hydrophobic to hydrophilic due to adsorption of the above substances. AFM imaged the aggregates on the surface and showed that lysozyme, in particular, penetrates the membrane pores, making them shallower and decreasing their porosity. The results of membrane potential measurements showed that lysozyme and albumin did not change the membrane charge state, but PAS-H changed it from negative to positive. The permeability coefficients of KCl and K2HPO4 varied significantly with the adsorption of each polyelectrolyte. In particular, the permeability coefficient of phosphate through the lysozyme-adsorbed membrane increased to twice that of the nonadsorbed membrane. Such polyelectrolyte adsorption on the membrane surface can be used for the modification of commercial artificial kidney phosphate extraction.

Evidence for the involvement of cyclic GMP in adenosine-induced, age-dependent vasodilatation

1. Adenosine-induced dilatation of rat aorta was present in aorta taken from 4 week-old rats, attenuated with increase in age of rats to 8 weeks, and was virtually absent in the aorta from 12 week-old rats. 2. Removal of the endothelium by mechanical rubbing attenuated adenosine-induced dilatation. 3. Haemoglobin and methylene blue partly reversed the adenosine-induced endothelium-dependent dilatation. 4. The order of potency of adenosine derivatives was 5'-(N-ethylcarboxamido)adenosine (NECA) greater than 2-phenylaminoadenosine (CV-1808) greater than 2-chloroadenosine greater than N6-([R]-[-]-phenylisopropyl)adenosine (R-PIA) greater than adenosine greater than N6-cyclohexyladenosine (CHA) greater than N6-([S]-[+]-phenylisopropyl)adenosine (S-PIA), indicating that adenosine receptors mediating the dilatation are of the A2 subtype. 5. [3H]-NECA bound to preparations of membranes from rats of 4 weeks old; it was displaced more effectively by NECA and the A2 ligand CV-1808 than by the A1 ligands CHA and S-PIA. ligands CHA and S-PIA. 6. The number but not affinity of specific binding sites for NECA decreased considerably with increase in age of rats to 8 weeks, and binding sites for [3H]-NECA were hardly detected in membrane preparations from rats of 20 weeks old. 7. Adenosine caused a marked increase in cyclic GMP production, but did not induce an increase in the cyclic AMP level. 8. This increase in cyclic GMP production induced by adenosine was abolished by methylene blue or 8-phenyltheophylline, or by removal of the endothelium. 9. The age-associated decrease in adenosine-induced dilatation was found to be associated with a reduction in the formation of cyclic GMP, but not of cyclic AMP. 10. These results suggest that adenosine causes dilatation via A2 receptors by inducing production of an endothelium-derived relaxing factor (EDRF), which in turn stimulates soluble guanylate cyclase, and so increases production of cyclic GMP. It is also suggested that the main reason for the age-associated decrease in adenosine-induced dilatation is a decrease in the number of A2-receptors or the ability of the endothelium to produce EDRF, leading to decreased production of cyclic GMP.

Dual effects of capsaicin on responses of the rabbit ear artery to field stimulation

1. The effects of capsaicin (Cap) on contractions of ring segments of rabbit ear artery induced by field stimulation were studied. 2. At low concentrations (0.3-3 microM) Cap caused transient enhancement and at higher concentrations (above 3 microM) inhibition of stimulation-induced contractions, without affecting noradrenaline (NA)-induced contractions. 3. In the continuous presence of high concentrations of Cap, rebound facilitation was observed after inhibition, and at this stage, Cap elicited less inhibition of the response. 4. Repeated application of Cap at 60 min intervals irreversibly desensitized the artery to the inhibitory effect of Cap. 5. Functional removal of the endothelium enhanced the facilitatory effect of low concentrations of Cap and attenuated its inhibitory effect. 6. Pretreatment with indomethacin abolished the facilitatory effect of Cap and enhanced its inhibitory effect, indicating that prostaglandins are involved in the action of Cap. The effect of indomethacin was more marked in preparations from which the endothelium had been removed. 7. Desensitization to substance P (SP) or substance K (SK), did not affect either the inhibitory or the facilitatory effect of Cap. 8. These results suggest that the dual effects of Cap on stimulation-induced contractions of rabbit ear artery may arise from the release of multiple mediators that act prejunctionally to modulate NA release. The stimulant effect seems to be mediated by prostanoids, while the inhibitory effect seems to be caused by a substance(s) that is not SP or SK. The possibility that the mediator is calcitonin gene-related peptide requires further study.

Age-associated decrease in histamine-induced vasodilation may be due to reduction of cyclic GMP formation

1. The effects of aging on histamine-induced vasodilatation and cyclic GMP production in rat thoracic aorta were investigated. 2. This histamine-induced dilatation of the aorta was mediated by H1-receptors and was dependent on the endothelium. 3. Histamine induced the greatest dilatation of arteries of 3-4 week old rats, progressively less of those of rats of 8 to 56 weeks old, and scarcely detectable dilatation of those of 100 week old rats. 4. Histamine induced cyclic GMP production in aorta from rats of 4 weeks old, with no change in the cyclic AMP level. This increase in the cyclic GMP level induced by histamine also decreased with age, being about 70% as great at 8 weeks, 50% as great at 50-60 weeks, and 10% as great at 130 weeks of age. 5. Removal of the endothelium completely abolished the histamine-induced increase in cyclic GMP. 6. The dilator effect of nitroprusside, which enhances cyclic GMP production by stimulating guanylate cyclase directly (not indirectly via the endothelium derived relaxing factor, EDRF), also showed age-related attenuation. 7. The dilator effect of 8-bromo cyclic GMP, which stimulates cyclic GMP-dependent protein kinase, also decreased during aging. 8. These results suggest that aging reduces the ability of the endothelium to produce EDRF, which stimulates guanylate cyclase, and so decreases cyclic GMP production. Thus the decreased dilator response of the arteries to histamine during aging is probably due to both loss of endothelial function and reduction of guanylate cyclase activity. Alteration of cyclic GMP-dependent protein kinase activity may also participate in the age-related changes.