β2-adrenergic stress evaluation of coronary endothelial-dependent vasodilator function in mice using 11C-acetate micro-PET imaging of myocardial blood flow and oxidative metabolism

Abstract

BackgroundEndothelial dysfunction is associated with vascular risk factors such as dyslipidemia, hypertension, and diabetes, leading to coronary atherosclerosis. Sympathetic stress using cold-pressor testing (CPT) has been used to measure coronary endothelial function in humans with positron emission tomography (PET) myocardial blood flow (MBF) imaging, but is not practical in small animal models. This study characterized coronary vasomotor function in mice with [11C]acetate micro-PET measurements of nitric-oxide-mediated endothelial flow reserve (EFRNOM) (adrenergic-stress/rest MBF) and myocardial oxygen consumption (MVO2) using salbutamol β2-adrenergic-activation.Methods[11C]acetate PET MBF was performed at rest + salbutamol (SB 0.2, 1.0 μg/kg/min) and norepinephrine (NE 3.2 μg/kg/min) stress to measure an index of MBF response. β-adrenergic specificity of NE was evaluated by pretreatment with α-adrenergic-antagonist phentolamine (PHE), and β2-selectivity was assessed using SB.ResultsAdjusting for changes in heart rate × systolic blood pressure product (RPP), the same stress/rest MBF ratio of 1.4 was measured using low-dose SB and NE in normal mice (equivalent to human CPT response). The MBF response was correlated with changes in MVO2 (p = 0.02). Nitric oxide synthase (NOS)-inhibited mice (Ng-nitro-L-arginine methyl ester (L-NAME) pretreatment and endothelial nitric oxide synthase (eNOS) knockout) were used to assess the EFRNOM, in which the low-dose SB- and NE-stress MBF responses were completely blocked (p = 0.02). With high-dose SB-stress, the MBF ratio was reduced by 0.4 following NOS inhibition (p = 0.03).ConclusionsLow-dose salbutamol β2-adrenergic-stress [11C]acetate micro-PET imaging can be used to measure coronary-specific EFRNOM in mice and may be suitable for assessment of endothelial dysfunction in small animal models of disease and evaluation of new therapies.

Impact of Image-Derived Input Function and Fit Time Intervals on Patlak Quantification of Myocardial Glucose Uptake in Mice

“…A similar method was used for evaluation of myocardial blood flow using 11 C-acetate in mice, resulting in reasonable estimation of input function for quantitative imaging (12). The shorter early frames used in the present study (2 vs. 10 s) may allow sharper definition of the vena cava activity peak and clearance.…”

Test–retest repeatability of myocardial blood flow and infarct size using 11C-acetate micro-PET imaging in mice

“…Using the time-frame acquired 11 C-acetate kinetic analysis. c Average arterial blood input functions and myocardium (means ± standard errors of the mean) following 11 C-acetate injection in healthy control mice [4]. Curves are normalized relative to the maximum activity of the reference standard (STD) carotid artery samples.…”

“…1a). The time-activity curve was shifted in time (+10 s) to account for the blood circulation delay from the VC to the LV myocardium, as validated recently [4]. LV polar maps of the 11 C-acetate uptake rate K 1 as an index of MBF (iMBF, millilitres per minute per gram), were generated using the IDIF of the LV cavity and inferior VC for comparison.…”

“…To validate the 11 C-acetate IDIF, the results of a previous study using manual blood sampling from the carotid artery and micro-PET scanning were re-analysed, including an IDIF positioned in the LV cavity [4]. All three arterial blood curves were used separately as input to the one-tissue compartment model (Fig.…”

“…Atherosclerosis, hypertension and diabetes all cause endothelial dysfunction in the early stages of disease. The endothelial nitric oxide synthase (eNOS) knockout transgenic mouse model is useful for assessing microvascular MBF responses in diseases in which coronary endothelial function is impaired, preventing autoregulation of the blood supply to adapt to local changes in demand [4]. The MI mouse model is used commonly to investigate adaptations and remodelling processes in the left ventricular (LV) myocardium after MI [5,6].…”