Nitrergic stimulation of the locus coeruleus modulates blood pressure and heart rate in the anaesthetized rat

To investigate whether nitric oxide is involved in the cardiovascular respo nses mediated via the locus coeruleus, the effects of microinjections of L- arginine and L-glutamate into the locus coeruleus on blood pressure and hea rt rate were investigated in sodium pentobarbitone-anaesthetized rats. Unil ateral microinjection of L-arginine (25, 50 nmol) elicited dose-related dep ressor (-17 +/- 4, -25 +/- 4 mmHg) and bradycardic (13 +/- 3, 24 +/- 6 b.p. m.) effects. Furthermore, these effects were attenuated by prior local micr oinjection of N-G-nitro-L-arginine (40 nmol). Peripheral muscarinic recepto r blockade with atropine methyl nitrate (1 mg/kg, i.v.) attenuated the brad ycardic but not the depressor responses to L-arginine. L-Glutamate (2 nmol) microinjections also mediated depressor (-27 +/- 6 mmHg) and bradycardic ( 53 +/- 23 b.p.m.) effects that were attenuated by microinjections of dizoci lpine maleate (1 nmol) into the locus coeruleus. In addition, pretreatment with N-G-nitro-L-arginine (40 nmol) also significantly attenuated the depre ssor response elicited by L-glutamate. These results suggest that nitrergic and glutamatergic pathways are operati ve within the locus coeruleus to modulate cardiovascular function, and also that a functional interaction may exist between the nitrergic and glutamat ergic systems within the rat locus coeruleus. (C) 1999 IBRO. Published by E lsevier Science Ltd.