Acute and chronic effects of morphine on cardiovascular system and the baroreflexes sensitivity during severe increase in blood pressure in rats

Abstract

BACKGROUND: This study aimed to determine the role and effects of baroreflexes during
acute 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 assigned
into 4 groups and the rats of the case group received morphine in the short and long term
periods, whereas the control rats received normal saline for the same duration. Then, the rats
were anesthetized, and their femoral artery and vein were cannulated for the injection of
phenylephrine and naloxone, respectively. The injection of phenylephrine was performed by the
device after a period of recording BP, mean arterial pressure (MAP), heart rate (HR) and
baroreflex sensitivity (BRS) in order to induce acute hypertension before and after injecting
naloxone. 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 may
cause significant reduction in systolic and diastolic arterial BP as well as the mean arterial
pressure; moreover, it significantly increased the sensitivity of baroreflexes. Furthermore, the
increased baroreflex sensitivity was observed after acute injection of morphine, whereas chronic
morphine injection caused reduction in baroreflex sensitivity.
CONCLUSION: It seems that the details of the opiates' effects on the body including
cardiovascular system depend on the type of opioids and consequently, on the type of stimulated
receptor.
Keywords: Morphine; Baroreflex Sensitivity; Blood Pressure