AJP - Regulatory, Integrative and Comparative Physiology, Vol 273, Issue 2 747-R754, Copyright © 1997 by American Physiological Society

ARTICLES

Effect of carbon dioxide on autonomic cardiovascular responses to systemic hypoxia in conscious rats

H. Hirakawa, T. Nakamura and Y. Hayashida
Department of Systems Physiology, University of Occupational and Environmental Health, Kitakyushu, Japan.

The contribution of the autonomic nervous system to the cardiovascular response to hypoxia with different levels of CO2 was investigated in conscious rats. Wistar rats were chronically instrumented for measurement of arterial blood pressure (ABP), electrocardiogram, and renal sympathetic nerve activity (RSNA). They were exposed to 1) hypocapnic hypoxia (Hypo), 2) isocapnic hypoxia (Iso), and 3) hypercapnic hypoxia (Hyper). Hypo caused a decrease in ABP, an increase in heart rate (HR) and RSNA, and a slight increase in plasma norepinephrine (NE). Iso caused no significant change in ABP or HR but did cause an increase in RSNA and plasma NE. Hyper caused an increase in ABP, a decrease in HR, and an increase in RSNA and plasma NE. In sinoaortic-denervated (SAD) rats, ABP and RSNA decreased and HR tended to decrease during Iso. SAD abolished the bradycardic response during Hyper. Atropine abolished the bradycardic response during Hyper, and HR tended to increase during all three kinds of hypoxia. In all three kinds of hypoxia, ABP and renal sympathetic nervous responses in atropine-treated rats were not significantly different from those in intact rats. These results indicate that Hypo causes sympathetic activation and parasympathetic inhibition while Iso and Hyper cause sympathetic and parasympathetic activation via peripheral chemoreceptors. The MABP-RSNA curve tended to shift to the left and the maximum gain of the baroreflex response tended to decrease during Hypo. In contrast, this curve shifted to the right and the maximum gain of the baroreflex response increased during Iso and Hyper, suggesting that baroreflex function is affected by arterial CO2 levels. We concluded that cardiovascular responses during hypoxia are modified by arterial Pco2 levels and mediated by the autonomic nervous system.

This article has been cited by other articles:

				D. B. Zoccal, L. G. H. Bonagamba, F. R. T. Oliveira, J. Antunes-Rodrigues, and B. H. Machado Increased sympathetic activity in rats submitted to chronic intermittent hypoxia Exp Physiol, January 1, 2007; 92(1): 79 - 85. [Abstract] [Full Text] [PDF]

				M. J. Campen, Y. Tagaito, T. P. Jenkins, A. Balbir, and C. P. O'Donnell Heart rate variability responses to hypoxic and hypercapnic exposures in different mouse strains J Appl Physiol, September 1, 2005; 99(3): 807 - 813. [Abstract] [Full Text] [PDF]

				E. H. Schlenker Integration in the PVN: another piece of the puzzle Am J Physiol Regulatory Integrative Comp Physiol, September 1, 2005; 289(3): R653 - R655. [Full Text] [PDF]

				L. F. Hayward and M. Von Reitzenstein c-Fos expression in the midbrain periaqueductal gray after chemoreceptor and baroreceptor activation Am J Physiol Heart Circ Physiol, November 1, 2002; 283(5): H1975 - H1984. [Abstract] [Full Text] [PDF]

				L.-Z. Hong, J.-S. Kuo, M.-H. Yen, and C.-Y. Chai Dorsomedial medulla is more susceptible than rostral ventrolateral medulla to hypoxic insult in cats J Appl Physiol, January 1, 2001; 90(1): 248 - 260. [Abstract] [Full Text] [PDF]

				D. C. Poole, W. L. Sexton, B. J. Behnke, C. S. Ferguson, K. S. Hageman, and T. I. Musch Respiratory muscle blood flows during physiological and chemical hyperpnea in the rat J Appl Physiol, January 1, 2000; 88(1): 186 - 194. [Abstract] [Full Text] [PDF]

				B. FLEMMING, E. SEELIGER, T. WRONSKI, K. STEER, N. ARENZ, and P. B. PERSSON Oxygen and Renal Hemodynamics in the Conscious Rat J. Am. Soc. Nephrol., January 1, 2000; 11(1): 18 - 24. [Abstract] [Full Text]

				A. Nishiyama, A. Miyatake, Y. Aki, T. Fukui, M. Rahman, S. Kimura, and Y. Abe Adenosine A1 Receptor Antagonist KW-3902 Prevents Hypoxia-Induced Renal Vasoconstriction J. Pharmacol. Exp. Ther., December 1, 1999; 291(3): 988 - 993. [Abstract] [Full Text]

				Y. Murasato, Y. Harada, M. Ikeda, Y. Nakashima, and Y. Hayashida Effect of Magnesium Deficiency on Autonomic Circulatory Regulation in Conscious Rats Hypertension, August 1, 1999; 34(2): 247 - 252. [Abstract] [Full Text] [PDF]

				Y. Murasato, H. Hirakawa, Y. Harada, T. Nakamura, and Y. Hayashida Effects of systemic hypoxia on R-R interval and blood pressure variabilities in conscious rats Am J Physiol Heart Circ Physiol, September 1, 1998; 275(3): H797 - H804. [Abstract] [Full Text] [PDF]