THE ADRENERGIC MECHANISM IN THE ROSTRAL VENTROLATERAL MEDULLA:A POSSIBLE ROLE IN STRESS-INDUSED PRESSOR RESPONSE AND TACHYCARDIA

Aim and Methods: This study attempts to find whether a microinjection of adrenaline (E) into the rostral ventrolateral medulla (rVLM) can or can't affect the blood pressure (BP) and heart rate (HR) of normal rats and analyzes the effects of the adrenergic mechanism in the rVLM on pressor response and tachycardia induced by stress in the rVLM. Experiments were performed on male SD rats. It was found that stress-induced changes of BP and HR could be hanging and restraining conscious rats with theire four limbs tied on a frame. Results: ①The pressor response and tachycadia could be induced by restrained conscious rats.②A microinjection of E into the bilateral rVLM resulted in an evident increase in BP and HR, which was blocked by a bilateral microinjection of α-adrenoceptor antagonist (phentolamine) into the same area, but not by β-adrenoceptor antagonist (propranoil). A microinjection of E of the same dosage into the bilateral caudal ventrolateral medulla (cVLM) or by intravenous of E of the same dosage had no such effect.③A pretreatment of rVLM area with hydroxydopamine (6-OHDA) abolished stress induced pressor and tachycardia.④The stress-induced pressor response and tachycadia could be abolished by microinjection of Phentolamine into the rVLM, but not by propranolol. Conclusion: The increase of BP and HR by microinjection of E into the rVLM or the stress-induced pressor response and tachycardia by restraininig may be mediated by activation of the α-adrenoceptor in rVLM.