Adrenergic stimulation of Rb+ uptake in pig hearts in vivo assessed by 87Rb MRS

It was previously shown that the adrenergic agonist dobutamine stimulates Rb+ uptake in isolated pig hearts. In the present work we examined whether dobutamine can increase Rb+ uptake rate in vivo. Open‐chest domestic pigs (N = 14) were used under general anesthesia. The surface coil was placed against the anterior left ventricular wall to obtain 87Rb spectra using a spectrometer interfaced with the 7T, 30‐cm horizontal bore magnet. RbCl was infused at the rate of 1.35 ± 0.14 mmol/kg/hr without or with dobutamine (0.6 mg/kg/hr) over a 60‐min period, and then the infusions were terminated. The rate constant (k × 103, from 13 ± 2.4 to 36 ± 12 min−1) and Rb+ influx rate (from 2.5% to 4.8%/min) were increased by dobutamine despite lower plasma [Rb+] (0.59 ± 0.16 vs. 0.84 ± 0.24 mM in control), while the tissue/plasma Rb ratios were identical (38 ± 9). Heart rate (HR) and systolic blood pressure (SBP) were increased from 106 ± 9 to 161 ± 15 bpm (+52%) and from 78 ± 7 to 93 ± 11 mmHg (+19%), respectively. The stimulation of Rb+ uptake by dobutamine is consistent with the activation of Na+/K+ ATPase previously observed in isolated hearts. However, the 50% increase in HR and the double coronary flow caused by the SBP increase and vasodilatation may also contribute to this effect. Magn Reson Med 53:817–822, 2005. © 2005 Wiley‐Liss, Inc.