The Cardiovascular Effects Of The Imidzaolines Microinjected Into The RVLM In Rats

In this study, we observed the effects on blood pressure (BP), heart rate (H7R) and arterial baroreflex (ABR) function after microinjection of various agonists and/or antagonists of imidazoline receptor with multi-barrel micropipette into the rostral ventrolateral medulla (RVLM) of male SD rats, which were anesthetized by urethane after pentobarbital induction. And it was found that 1) clonidine, agmatine, and idazoxin decreased mean arterial pressure (MAP) and HR when microinjected unilaterally into the RVLM respectively; 2) clonidine, agmatine, and idazoxin inhibited the effect of BP elevation elicited by unilateral glutamate microinjection into the RVLM, when microinjected into the same region of the RVLM; 3) clonidine, agmatine, idazoxin, and MK-801 could partially or completely block the reaction of ABR induced by stimulation of aortic nerve when microinjected bilaterally into the RVLM; 4) idazoxin could completely 5 antagonized the effect of BP reduction caused by clonidine and agmatine, while MK-801 did not influence on BP reduction produced by clonidine and agmatine; 5) neither clonidine nor agmatine had effect on BP elevation caused by N-methyl-D-aspartate (NMDA) in general doses (O.5M, lOOuI) however at higher doses (O.5M, 200u1) both of them abolished the effects of NMDA. These results suggest that 1) the effects of BP reduction produced by clonidine, agmatine, or idazoxin microinjection into RVLM is mediated I~- imidazoline receptor; 2) idazoxin may be a partial agonist of imidazoline receptor; 3) NMDA receptor in the RVLM may involve the effects of clonidine, agmatine, and idazoxin on BIP, KR, and ABR, and further it may also modulate the action of clonidine, agmatine, and idazoxin on BP caused by glutamate as well; 4)agmatine might be a novel endogeneoue ligand of imidazoline receptor.