Ali Asghar Pour Shanazari - Associate Professor, Department of Physiology, School of Medicine, Isfahan University of Medical Sciences, Isfahan, Iran.
Zahra Aslani - MD, Health City Center, Fereydonshahr, Iran
Efat Ramshini - MSc in Physiology, Department of Physiology, School of Medicine, Isfahan University of Medical Sciences, Isfahan, Iran
Hojatolah Alaei - Professor, Department of Physiology, School of Medicine, Isfahan University of Medical Sciences, Isfahan, Iran

BACKGROUND: This study aimed to determine the role and effects of baroreflexes duringacute increase in blood pressure (BP) after severe and long-term infusion of morphine.METHODS: This experimental study was conducted on male desert rats. They were assignedinto ۴ groups and the rats of the case group received morphine in the short and long termperiods, whereas the control rats received normal saline for the same duration. Then, the ratswere anesthetized, and their femoral artery and vein were cannulated for the injection ofphenylephrine and naloxone, respectively. The injection of phenylephrine was performed by thedevice after a period of recording BP, mean arterial pressure (MAP), heart rate (HR) andbaroreflex sensitivity (BRS) in order to induce acute hypertension before and after injectingnaloxone. The Student t-test and analysis of variance (ANOVA) were used for statistical analysis.RESULTS: The obtained results suggested that acute and chronic injections of morphine maycause significant reduction in systolic and diastolic arterial BP as well as the mean arterialpressure; moreover, it significantly increased the sensitivity of baroreflexes. Furthermore, theincreased baroreflex sensitivity was observed after acute injection of morphine, whereas chronicmorphine injection caused reduction in baroreflex sensitivity.CONCLUSION: It seems that the details of the opiates' effects on the body includingcardiovascular system depend on the type of opioids and consequently, on the type of stimulatedreceptor.Keywords: Morphine; Baroreflex Sensitivity; Blood Pressure