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NEUROHUMORAL CONTROL OF CARDIOVASCULAR FUNCTION

Role of pressor mechanisms from the NTS and CVLM in control of arterial pressure

¹Department of Physiology, Universidade Federal de São Paulo - Escola Paulista de Medicina, São Paulo, Brazil; ²Department of Physiology and Pathology, Faculdade de Odontologia, Universidade Estadual Paulista-UNESP, Araraquara, Brazil; and ³Department of Physiology, Faculdade de Medicina do ABC, Santo André, Brazil

Submitted 26 January 2005 ; accepted in final form 12 July 2005

In the present study, we investigated the effects of inhibition of the caudal ventrolateral medulla (CVLM) with the GABA_A agonist muscimol combined with the blockade of glutamatergic mechanism in the nucleus of the solitary tract (NTS) with kynurenic acid (kyn) on mean arterial pressure (MAP), heart rate (HR), and regional vascular resistances. In male Holtzman rats anesthetized intravenously with urethane/chloralose, bilateral injections of muscimol (120 pmol) into the CVLM or bilateral injections of kyn (2.7 nmol) into the NTS alone increased MAP to 186 ± 11 and to 142 ± 6 mmHg, respectively, vs. control: 105 ± 4 mmHg; HR to 407 ± 15 and to 412 ± 18 beats per minute (bpm), respectively, vs. control: 352 ± 12 bpm; and renal, mesenteric and hindquarter vascular resistances. However, in rats with the CVLM bilaterally blocked by muscimol, additional injections of kyn into the NTS reduced MAP to 88 ± 5 mmHg and mesenteric and hindquarter vascular resistances below control baseline levels. Moreover, in rats with the glutamatergic mechanisms of the NTS blocked by bilateral injections of kyn, additional injections of muscimol into the CVLM also reduced MAP to 92 ± 2 mmHg and mesenteric and hindquarter vascular resistances below control baseline levels. Simultaneous blockade of NTS and CVLM did not modify the increase in HR but also abolished the increase in renal vascular resistance produced by each treatment alone. The results suggest that important pressor mechanisms arise from the NTS and CVLM to control vascular resistance and arterial pressure under the conditions of the present study.

ventrolateral medulla; ; -aminobutyric acid; L-glutamate; muscimol; sympathetic system

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