RT Journal Article
SR Electronic
T1 PET of (<em>R</em>)-<sup>11</sup>C-Rolipram Binding to Phosphodiesterase-4 Is Reproducible and Sensitive to Increased Norepinephrine in the Rat Heart
JF Journal of Nuclear Medicine
JO J Nucl Med
FD Society of Nuclear Medicine
SP 263
OP 269
DO 10.2967/jnumed.110.082701
VO 52
IS 2
A1 Adam J. Thomas
A1 Jean N. DaSilva
A1 Mireille Lortie
A1 Jennifer M. Renaud
A1 Miran Kenk
A1 Rob S. Beanlands
A1 Robert A. deKemp
YR 2011
UL http://jnm.snmjournals.org/content/52/2/263.abstract
AB Phosphodiesterase-4 (PDE4) plays a critical role in the regulation of β-adrenergic receptor–stimulated cyclic adenosine monophosphate cell signaling in the heart. (R)-rolipram, a PDE4-selective inhibitor, has been studied previously as a radiotracer for the quantification of PDE4 levels. The aim of this study was to characterize (R)-11C-rolipram binding in the rat myocardium in vivo, using small-animal PET. Methods: Male Sprague–Dawley rats (n = 30) were administered (R)-11C-rolipram and imaged for 60 min to evaluate tracer binding and reproducibility, quantified using Logan slope analysis of the distribution volume. Dynamic 13N-ammonia imaging was performed to quantify myocardial blood flow and assist in cardiac regional analysis. Saturation studies evaluated the sensitivity of (R)-11C-rolipram to PDE4 blocking by unlabeled cold (R)-rolipram (0.0001–1.0 mg/kg), for estimation of the median effective dose (ED50) in the heart. (R)-11C-rolipram response to enhanced norepinephrine stimulation of the β-adrenergic receptor with desipramine (20 mg/kg, intravenous) was also studied. Intrarat variability studies (n = 5) were conducted with test–retest imaging at 16 ± 7 d. Results: A reduction of Logan slope was observed with increasing cold mass coadministered with the tracer, with an ED50 of 0.0019 mg/kg (95% confidence interval, 0.0014–0.0052) estimated from the saturation studies. This ED50 predicted less than 10% enzyme occupancy at 0.0002 mg of cold (R)-rolipram per kilogram (mass/body weight). Low-occupancy imaging at 0.00018 ± 0.00002 mg/kg produced a mean Logan slope of 5.5 ± 0.85 mL/cm3. Enzyme saturation of more than 90%, compared with low-occupancy conditions, occurred at more than 0.02 mg/kg, with a complete blocking dose (&gt;1 mg of (R)-rolipram per kilogram) resulting in a Logan slope of 3.3 ± 0.1 mL/cm3, representing a 40% reduction. Compared with baseline, a Logan slope of 6.8 ± 0.7 mL/cm3 in desipramine-challenged animals was observed, representing a 30% increase due to acute norepinephrine stimulation, despite a reduction in myocardial blood flow. Intrarat and intraoperator variability was less than 5% between repeated measures. Conclusion: (R)-11C-rolipram shows the ability to monitor increases and decreases in PDE4 availability in the rat myocardium, with good reproducibility.