A. Schäfer

Effect of YC-1, an NO-independent, superoxide-sensitive stimulator of soluble guanylyl cyclase, on smooth muscle responsiveness to nitrovasodilators

1 We studied the effects of 3‐(5′‐hydroxymethyl‐2′furyl)‐1‐benzyl indazole (YC‐1) on the activity of purified soluble guanylyl cyclase (sGC), the formation of guanosine‐3′: 5′cyclic monophosphate (cyclic GMP) in vascular smooth muscle cells (VSMC), and on the tone of rabbit isolated aortic rings preconstricted by phenylephrine (PE). In addition, we assessed the combined effect of YC‐1, and either NO donors, or superoxide anions on these parameters. 2 YC‐1 elicited a direct concentration‐dependent activation of sGC (EC50 18.6 ± 2.0 μm), which was rapid in onset and quickly reversible upon dilution. YC‐1 altered the enzyme kinetics with respect to GTP by decreasing Km and increasing Vmax. Activation of sGC by a combination of sodium nitroprusside (SNP) and YC‐1 was superadditive at low and less than additive at high concentrations, indicating a synergistic activation of the enzyme by both agents. A specific inhibitor of sGC, 1H‐(1,2,4)‐oxdiazolo‐(4,3‐a)‐6‐bromo‐quinoxazin‐l‐one (NS 2028), abolished activation of the enzyme by either compound. 3 YC‐1 induced a concentration‐dependent increase in intracellular cyclic GMP levels in rat cultured aortic VSMC, which was completely inhibited by NS 2028. YC‐1 applied at the same concentration as SNP elicited 2.5 fold higher cyclic GMP formation. Cyclic GMP‐increases in response to SNP and YC‐1 were additive. 4 YC‐1 relaxed preconstricted endothelium‐denuded rabbit aortic rings in a concentration‐dependent manner (50% at 20 μM) and markedly increased cyclic GMP levels. Relaxations were inhibited by NS 2028. A concentration of YC‐1 (3 μm), which elicited only minor effects on relaxation and cyclic GMP, increased the vasodilator potency of SNP and nitroglycerin (NTG) by 10 fold and markedly enhanced SNP‐and NTG‐induced cyclic GMP formation. 5 Basal and YC‐1‐stimulated sGC activity was sensitive to inhibition by superoxide (O2−) generated by xanthine/xanthine oxidase, and was protected from this inhibition by superoxide dismutase (SOD). YC‐1‐stimulated sGC was also sensitive to inhibition by endogenously generated (O2− in rat preconstricted endothelium‐denuded aortic rings. Relaxation to YC‐1 was significantly attenuated in aortae from spontaneously hypertensive rats (SHR), which generated O2− at a higher rate than aortae from normotensive Wistar Kyoto rats (WKY). SOD restored the vasodilator responsiveness of SHR rings to YC‐1. 6 In conclusion, these results indicate that YC‐1 is an NO‐independent, O2−‐sensitive, direct activator of sGC in VSMC and exerts vasorelaxation by increasing intracellular cyclic GMP levels. The additive or even synergistic responses to NO‐donors and YC‐1 in cultured VSMC and isolated aortic rings apparently reflect the direct synergistic action of YC‐1 and NO on the sGC. The synergism revealed in this in vitro study suggests that low doses of YC‐1 may be of therapeutic value by permitting the reduction of nitrovasodilator dosage.

ELECTRIC AND MAGNETIC POLARIZABILITY OF THE NUCLEON IN THE MIT BAG MODEL

The eleciric and magnetic polarizabilities of the proton and neutron arc calculated in the framework of the MIT hag model. Neglecting vacuum-polarization we get a~ = a, = 10.8 xlO“ fm3, s~ = 2.3x 10“ fm3 and s =1.5 x 10“ fm3, in good agreement with experiment. The difficulties in treating the vacuum-polarization consistently are discussed. lt is argued that the polarizabilities may offer a possibility to measure the effective size of nuclcon bags inside of nuclei. In this work we calculate the electric and mag netic polarizabilities a and

QCD sum rule calculation of twist-4 corrections to Bjorken and Ellis-Jaffe sum rules

in the framework of the MIT hag model [1]. This model and other more refined hag models arc justified mainly by their success in predicting the bw energy spectrum of hadrons and their properties like magnetic mo ments and rms charge radii, etc. [2]. In this respect it is very interesting to investigate the polarizabili ties, because they are much more sensitive to the details of the model. As second order effects they test the level-structure near the ground state and transition matrix elements between the ground ar excited states. Being proportional to the cube o~ .te hag radius they can also be regarded as a measure of the size of the bag. To support this statement let us note that it would be highly interesting to deduce the polariza bilities of nucleons bound in nuclei, e.g. from Compton scattering data for energies just below the pion-production threshold. From the ratio (~ + s)nuciei/(& ±

IR-renormalon contribution to the longitudinal structure function FL

Abstract We calculate the twist-4 corrections to the integral of g 1 ( x , Q 2 ) in the framework of QCD sum rules using an interpolating nucleon field which contains explicitly a gluonic degree of freedom. This information can be used together with previous calculations of the twist-3 contribution to the second moment of g 2 ( x ) to estimate the higher-twist corrections to the Ellis-Jaffe and Bjorken sum rules. We get f (2) (proton) = −0.037 ±0.006 and f (2) (neutron) = −0.013 ± 0.006. Numerically ou results roughly agree with those obtained by Balitsky, Braun and Kolesnichenko based on a sum rule for a simpler current. Our calculations are far more stable as tested within the sum rule approach but are more sensitive to less well known condensates.

The chiral phase transition in a random matrix model with molecular correlations

Abstract The available data on F L suggest the existence of unexpected large higher twist contributions. We use the 1 N f expansion to analyze the renormalon contribution to the coefficient function of the longitudinal structure function F L p − n . The renormalon ambiguity is calculated for all moments of the structure function thus allowing to estimate the contribution of “genuine” twist-4 corrections as a function of Bjorken- x . The predictions turn out to be in surprisingly good agreement with the experimental data.

Single spin asymmetry for the Drell-Yan process

Abstract The chiral phase transition of QCD is analyzed in a model combining random matrix elements of the Dirac operator with specially chosen non-random ones. The special form of the latter is motivated by the assumption that the fermionic quasi-zero modes associated with instanton and anti-instanton configurations determine the chiral properties of QCD. Our results show that the degree of correlation between these modes plays the decisive role. To reduce the value of the chiral condensate by more than a factor of 2 about 95 percent of the instantons and anti-instantons must form so-called molecules. This conclusion agrees with numerical results of the Stony Brook group.

Is there evidence for the production of a new particle in heavy-ion collisions?

Abstract We calculated the single spin asymmetries for the reaction P + P(↑) → l l + X in the framework of twist-3 QCD for HERA energies. The necessary imaginary phase is produced by the on-shell contribution of the quark propagator, while the long distance part is analogous to that providing the direct photon asymmetry calculated by J. Qiu and G. Sterman [Nucl. Phys. B 378 (1992) 52]. The asymmetry turns out to be generally of the order percent.

Phenomenology of IR-renormalons in inclusive processes

The possibility of the production of a new neutral elementary particle in heavy-ion collisions is discussed.

OPE analysis for polarized deep inelastic scattering

Measurements of QCD observables have reached such high precision that power corrections to the structure functions can often be extracted with a reasonable accuracy from the existing data. The situation on the theoretical side is much less clear. In the best understood case of deep inelastic scattering, the relevant contributions can be attributed in the framework of operator product expansion (OPE) to matrix elements of higher-twist operators [1], but their determination in QCD is ambiguous due to occurrence of power divergences [2]. From the phenomenological point of view, however, attempts to compute these matrix elements using e.g., QCD sum rules have provided results which seem to have at least the right order of magnitude [3] as compared with available experimental estimates.

Non—Perturbative Effects in the SU(3)—Gluon Plasma

We present an explicit OPE analysis for the first moment of g1 up to order M2Q2. This result allows to calculate power corrections to the Bjorken and Ellis-Jaffe sum rules.