Responsiveness of α2-adrenoceptor/I1-imidazoline receptor in the rostral ventrolateral medulla to cardiovascular regulation is enhanced in conscious spontaneously hypertensive rat

ABSTRACTStimulation of α2-adrenoceptor/I1-imidazoline receptors in the rostral ventrolateral medulla decreases the blood pressure via sympathoinhibition. However, alteration of receptor responses in genetically hypertensive rats remains unclear. We examined cardiovascular responses of α2-adrenoceptor/I1-imidazoline receptor agonist and antagonists microinjected into the rostral ventrolateral medulla of conscious spontaneously hypertensive rats and normotensive Wistar Kyoto rats. Injection of 2-nmol clonidine—an α2-adrenoceptor/I1-imidazoline receptor agonist—unilaterally into the rostral ventrolateral medulla decreased the blood pressure, heart rate, and renal sympathetic nerve activity; the responses were significantly enhanced in spontaneously hypertensive rats than in Wistar Kyoto rats. Co-injection of 2-nmol 2-methoxyidazoxan (a selective α2-adrenoceptor antagonist) or 2-nmol efaroxan (an I1-receptor antagonist) with 2 nmol of clonidine attenuated the hypotensive and bradycardic effects of clonidine-o...