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First published online on August 17, 2006.
Experimental Physiology (2006)
DOI: 10.1113/expphysiol.2006.034611
© The Physiological Society 2006
A more recent version of this article appeared on November 1, 2006
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Received June 1, 2006
Revised July 1, 2006
Accepted after revision August 14, 2006

Cardiovascular Control [210]

ROLE OF MEDULLARY CATECHOLAMINERGIC NEURONS IN CARDIOVASCULAR RESPONSES INDUCED BY ACUTE CHANGES IN CIRCULATING VOLUME

Gustavo R Pedrino 1, Isabela Maurino 1, Debora S Colombari 2, Sergio L Cravo 1*

1 Universidade Federal de São Paulo-Escola Paulista de Medicina
2 Faculdade de Odontologia, Universidade Estadual Paulista

* To whom correspondence should be addressed. E-mail: sldcravo{at}fcr.epm.br.


  Abstract
Several findings suggest that catecholaminergic neurons in the caudal ventrolateral medulla (CVL) contribute to body fluid homeostasis and cardiovascular regulation. The present study sought to determine the effects of lesions of these neurons on the cardiovascular responses induced by changes in circulating volume. All experiments were performed in male Wistar rats (320-360g). Medullary catecholaminergic neurons were lesioned by microinjection of anti-D{beta}H-saporin (SAP-rats, 6.3{eta}g/60{eta}l, N=14) into the CVL, whereas sham rats received microinjections of free saporin (1.3{eta}g/60{eta}l, N=15). Two weeks later, rats were anesthetized (urethane 1.2g/kg, iv), instrumented for measurement of arterial pressure (MAP), renal blood flow (RBF) and vascular conductance (RVC), and infused with hypertonic saline (HS; 3M NaCl, 0.18ml/100g bw, iv) or an isotonic solution (VE, 4% Ficoll, 1% of bw, iv). In sham rats HS induced sustained increases in RBF and RVC (155±7 and 145±6% of baseline, 20min after HS). In SAP-rats RBF responses to HS were blunted (125±6%) and RVC increases were abolished (108±5%) 20 minutes after HS. VE increased RBF and RVC in sham-rats (149±10 and 145±12% of baseline, 20min). These responses were reduced in SAP-rats (131±6 and 126±5%, 20min). Pressor responses to HS were larger in SAP-rats than in sham rats (17±5 vs. 9±2mmHg; 20min) whereas during VE these responses were similar in both groups (6±3 vs. 4±6mmHg, 20min). Immunohistochemical analysis indicates that microinjections of anti-D{beta}H-saporin produced extensive destruction within the A1/C1 cell groups in the CVL. These results suggest that catecholaminergic neurons mediate the renal vasodilation that follows acute changes in the volume and composition of the extracellular compartment.

Key Words: Osmoregulation, Vascular blood flow, Ventrolateral medulla






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