Ractopamine (RAC), a β-adrenergic agonist, has been used as a feed additive to increase muscle mass and decrease body fat. However, the data about adverse effects of RAC have been limited and only in healthy animals and human subjects. In this study, we compared the hemodynamic effects of RAC in healthy and atherosclerotic Wistar Kyoto (WKY) rats, and spontaneously hypertensive rats (SHRs).
Male healthy WKY rats, atherosclerotic WKY rats, SHRs were administered with RAC at dosage levels of 0, 3, 9 and 27 mg/kg body weight by gastric intubation. Hemodynamic parameters including heart rate (HR), cardiac output (CO), peripheral vascular resistance (TPR) and systolic blood pressure (SBP) were measured using a high-fidelity pressure-volume catheter positioned in the chamber of left ventricle, and two high-fidelity pressure transducers at the left carotid and femoral arteries of each rat. Data were collected from 5 minutes (min) before exposure to 60 min after exposure. The data were analyzed on a beat-to-beat basis and reported as 2- or 5- min periods.
Increase of HR and CO, and decrease of TPR were observed since the first 5-10 min in the high-dose groups for healthy rats, and SBP was significantly decreased at the early experimental period then returned to the baseline. While in the SHRs, the changes of HR, CO and TRP were more prominent as compared to healthy rats, and SBP remained low through the observation period. The changes of HR, CO and TRP in atherosclerotic WKY rats were similar to healthy rats, except for the increase of TRP in the moderate dose group. Thus, SBP was not decreased for the high dose group, while SBP was elevated in the moderate-dose group.
Our results suggest that subjects with cardiovascular risk factors may be more susceptible to the adverse effects of RAC. Thus, the safety factor for RAC regulation needs to be further evaluated in the susceptible population with cardiovascular diseases including myocardial infarction and congestive heart failure.