Rostral ventrolateral medulla : A source of sympathetic activation in rats subjected to long-term treatment with L-NAME.
The major aim of the present study was to evaluate the role of the rostral ventrolateral medulla (RVLM) in the maintenance of hypertension in rats subjected to long-term treatment with N(G)-nitro-L-arginine methyl ester (L-NAME) (70 mg/kg orally for 1 week). We inhibited or stimulated RVLM neurons with the use of drugs such as glycine, L-glutamate, or kynurenic acid in urethane-anesthetized rats (1.2 to 1.4 g/kg IV). Bilateral microinjection of glycine (50 nmol, 100 nL) into the RVLM of hypertensive rats produced a decrease in mean arterial blood pressure (MAP) from 158+/-4 to 71+/-4 mm Hg (P<0.05), which was similar to the decrease produced by intravenous administration of hexamethonium. In normotensive rats, glycine microinjection reduced MAP from 106+/-4 to 60+/-3 mm Hg (P<0.05). Glutamate microinjection into the RVLM produced a significant increase in MAP in both hypertensive rats (from 157+/-3 to 201+/-6 mm Hg) and normotensive rats (from 105+/-5 to 148+/-9 mm Hg). No change in MAP was observed in response to kynurenic acid microinjection into the RVLM in either group. These results suggest that hypertension in response to long-term L-NAME treatment is dependent on an increase in central sympathetic drive, mediated by RVLM neurons. However, glutamatergic synapses within RVLM are probably not involved in this response.
Bergamaschi
C T
CT
Department of Physiology, UNIFESP, Escola Paulista de Medicina, São Paulo, Brazil. cassia@fisiocardio.epm.br
Campos
R R
RR
Lopes
O U
OU
D000818:Animals; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D018698:Glutamic Acid / Q000494:pharmacology; D005998:Glycine / Q000494:pharmacology; D006973:Hypertension / Q000209:etiology / Q000503:physiopathology*; D007736:Kynurenic Acid / Q000494:pharmacology; D008297:Male; D008526:Medulla Oblongata / Q000503:physiopathology*; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology*; D051381:Rats; D017208:Rats, Wistar; D013564:Sympathetic Nervous System / Q000503:physiopathology*
D004791:Enzyme Inhibitors; D018691:Excitatory Amino Acid Antagonists; D018698:Glutamic Acid; D007736:Kynurenic Acid; D005998:Glycine; D019331:NG-Nitroarginine Methyl Ester