Effect of adenosine antagonism on metabolically mediated coronary vasodilation in humans

AbstractObjectives. This study was performed io assess the importance of adenosine in mediating metabolic coronary vasodilation during atrial pacing stress in humans.Background. Numerous animal studies have examined the role of adenosine in the regulation of coronary blood flow, with inconsistent results.Methods. The effect of the adenosine antagonist aminophylline (6 mg/kg body weight intravenously) on coronary functional hyperemia during rapid atrial pacing was determined in 12 patients. The extent of inhibition of adenosine vasodilation was assessed using graded intracoronary adenosine infusions before and after aminophylline administration in seven patients. Coronary blood flow changes were measured with a 3F intracoronary Doppler catheter.Results. After aminophylline administration, the increase in coronary flow velocity during adenosine infusions was reduced from 84 ± 48% (mean ± SD) to 21 ± 31% above control values (p < 0.001) at 10 μg/min and from 130 ± 39% to 59 ± 51% above control values (p < 0.001) at 40 μg/min. During rapid atrial pacing under control conditions, coronary blood flow velocity increased by 26 ± 16%. The flow increment during paced tachycardia after aminophylline (23 ± 10%) was unchanged from the control value, despite substantial antagonism of adenosine coronary dilation by aminophylline.Conclusions. These data suggest that adenosine does not play an important role in the regulation of coronary blood flow in response to rapid atrial pacing in humans

The Isgur-Wise function in a relativistic model for qQˉq\bar Q system

We use the Dirac equation with a ``(asymptotically free) Coulomb + (Lorentz scalar) linear '' potential to estimate the light quark wavefunction for $q\bar Q$ mesons in the limit $m_Q\to \infty$. We use these wavefunctions to calculate the Isgur-Wise function $\xi (v.v^\prime )$ for orbital and radial ground states in the phenomenologically interesting range $1\leq v.v^ \prime \leq 4$. We find a simple expression for the zero-recoil slope, $\xi^ \prime (1) =-1/2- \epsilon^2 /3$, where $\epsilon$ is the energy eigenvalue of the light quark, which can be identified with the $\bar\Lambda$ parameter of the Heavy Quark Effective Theory. This result implies an upper bound of $-1/2$ for the slope $\xi^\prime (1)$. Also, because for a very light quark $q (q=u, d)$ the size $\sqrt {}$ of the meson is determined mainly by the ``confining'' term in the potential $(\gamma_\circ \sigma r)$, the shape of $\xi_{u,d}(v.v^\prime )$ is seen to be mostly sensitive to the dimensionless ratio $\bar \Lambda_{u,d}^2/\sigma$. We present results for the ranges of parameters $150 MeV <\bar \Lambda_{u,d} <600 MeV$ $(\bar\Lambda_s \approx \bar\Lambda_{u,d}+100 MeV)$, $0.14 {GeV}^2 \leq \sigma \leq 0.25 {GeV}^2$ and light quark masses $m_u, m_d \approx 0, m_s=175 MeV$ and compare to existing experimental data and other theoretical estimates. Fits to the data give: ${\bar\Lambda_{u,d}}^2/\sigma =4.8\pm 1.7$, $-\xi^\prime_{u,d}(1)=2.4\pm 0.7$ and $\vert V_{cb} \vert \sqrt {\frac {\tau_B}{1.48 ps}}=0.050\pm 0.008$ [ARGUS '93]; ${\bar\Lambda_{u,d}}^2/\sigma = 3.4\pm 1.8$, $-\xi^\prime_{u,d}(1)=1.8\pm 0.7$ and $\vert V_{cb} \vert \sqrt { \frac {\tau_B}{1.48 ps}}=0.043\pm 0.008$ [CLEO '93]; ${\bar\Lambda_{u,d}}^2/Comment: 22 pages, Latex, 4 figures (not included) available by fax or via email upon reques

Decay constants and mixing parameters in a relativistic model for q\barQ system

We extend our recent work, in which the Dirac equation with a ``(asymptotically free) Coulomb + (Lorentz scalar $\gamma_0\sigma r$) linear '' potential is used to obtain the light quark wavefunction for $q\bar Q$ mesons in the limit $m_Q\to \infty$, to estimate the decay constant $f_P$ and the mixing parameter $B$ of the pseudoscalar mesons. We compare our results for the evolution of $f_P$ and $B$ with the meson mass $M_P$ to the non-relativistic formulas for these quantities and show that there is a significant correction in the subasymptotic region. For $\sigma =0.14{{\rm ~GeV}}^{-2}$ and \lms =0.240{\rm ~GeV} we obtain: $f_D =0.371\; ,\; f_{D_s}=0.442\; ,\; f_B=0.301\; ,\; f_{B_s}=0.368 {\rm ~GeV}$ and $B_D=0.88\; ,\; B_{D_s}=0.89\; ,\; B_B=0.95\; ,\; B_{B_s}=0.96\; ,\;$ and $B_K=0.60$.Comment: 13 pages, Latex, 3 figures (included