198 Endogenous Vasopressin Modulates the Cardiovascular Responses to Exercise LISETE COMPAGNO MICHELINI a,c AND MARIANA MORRIS b a Department of Physiology and Biophysics, ICB, University of São Paulo, 05508-900, São Paulo, SP, Brazil b Department of Pharmacology and Toxicology, Wright State University School of Medicine, Dayton, Ohio 45401-0927, USA ABSTRACT: The role of brain-stem vasopressinergic projections in the genesis of reflex bradycardia and in the modulation of heart rate control during exer- cise is discussed on the basis of both changes in endogenous peptide content and heart rate changes observed during exercise. Dynamic running caused an in- crease in vasopressin content specifically in dorsal and ventral brain-stem ar- eas. Rats pretreated with vasopressin or the V 1 receptor antagonist into the nucleus tractus solitarii (NTS) showed a significant potentiation or a marked blunting of the exercise tachycardia, respectively, without any change in the blood pressure response. It is proposed that long-descending vasopressinergic pathways from the hypothalamus to the NTS serves as one link between the two main neural controllers of the circulation, that is, the central command and feedback control mechanisms driven by the peripheral receptors signals. Therefore vasopressinergic input contributes to the adjustment of heart rate response (and cardiac output) to the circulatory demand during exercise. INTRODUCTION It is well known that cardiac output, total peripheral resistance and venous capac- itance are regulated on a moment-to-moment basis to keep blood pressure and vol- ume in a narrow range, maintaining adequate blood supply to different vasculatures. 1–3 To maintain blood pressure and adjust flow efficiently, the central nervous system (CNS) processes peripheral information on pressure, blood gases, pH, volume, temperature, etc. conveyed by different sets of receptors such as barore- ceptors, chemoreceptors, cardiopulmonary receptors, and others. This information is integrated in different areas and at different levels of the CNS to provide adequate changes in sympathetic and parasympathetic tone to the heart and blood vessels, the main effectors of circulatory control. 3 c Address for correspondence: Lisete C. Michelini, Ph.D., Dep. Fisiologia e Biofísica, ICB- USP, Av. Prof. Lineu Prestes, 1524, 05508-900, São Paulo, SP, Brasil. Phone: 55-11-818-7213; fax: 55-11-818-7285. e-mail: michelin@usp.br