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(Hypertension. 1997;30:704.)
© 1997 American Heart Association, Inc.

Articles

Excitatory Effects of Nitric Oxide Within the Rostral Ventrolateral Medulla of Freely Moving Rats

Marli C. Martins-Pinge; Izabel Baraldi-Passy; Oswaldo U. Lopes

From the Department of Physiology, Universidade Federal de São Paulo, Escola Paulista de Medicina, São Paulo, Brazil.

Correspondence to Oswaldo U. Lopes, MD, Departamento de Fisiologia, Universidade Federal de São Paulo, Escola Paulista de Medicina, Rua Botucatu, 862, CEP 04023-060, São Paulo, SP, Brazil. E-mail LopesU.Fisi{at}epm.br

Abstract The aim of the present study was to examine the participation of NO in the rostral ventrolateral medulla (RVLM) of freely moving rats. We utilized NO donors and L-arginine, which were microinjected into the RVLM. Unilateral microinjection (100 nL) of 2.5 nmol sodium nitroprusside produced a biphasic response consisting of an initial, rapid increase in arterial pressure (AP) from 125±5 to 161±8 mm Hg (P<.01) and a second, long-lasting response with a progressive increase in AP (maximum peak, 34±9 mm Hg; P<.01). Another NO donor, S-nitroso-N-acetylpenicillamine (SNAP; 2.5 nmol), also produced immediate hypertension from 118±5 mm Hg to 168±7 mm Hg (P<.01) but without the second, long-lasting response. L-Arginine (5, 24, and 140 nmol) produced a gradual increase in AP. L-Glutamate (5 nmol) microinjected into the RVLM produced an increase in AP from 122±9 mm Hg to 171±8 mm Hg (P<.01) and bradycardia from 342±10 to 315±8 beats/min. This AP response was significantly attenuated, from 115±7 to 128±9 mm Hg (P<.05), after microinjection of methylene blue (3 nmol) without alterations in heart rate. These results indicate that NO may have an excitatory effect on the RVLM of freely moving rats, probably in association with glutamatergic synapses via cGMP mechanisms.

Key Words: amino acids • blood pressure, arterial • brain • nitric oxide • rostral ventrolateral medulla

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