Sympathetic-mediated hypertension of awake juvenile rats submitted to chronic intermittent hypoxia is not linked to baroreflex dysfunction

Author(s)

Zoccal, Daniel B. ^[1] ; Bonagamba, Leni G. H. ^[1] ; Paton, Julian F. R. ^[2] ; Machado, Benedito H. ^[1]

Affiliation

^[1] Univ Sao Paulo, Sch Med, Dept Physiol, BR-14049900 Ribeirao Preto, SP - Brazil

^[2] Univ Bristol, Sch Med Sci, Bristol Heart Inst, Dept Physiol & Pharmacol, Bristol BS8 1TD, Avon - England

• Document type: Journal article
• Source: Experimental Physiology; v. 94, n. 9, p. 972-983, SEP 1 2009.
• Web of Science Citations: 68

Abstract

In the present study, we evaluated the mechanisms underpinning the hypertension observed in freely moving juvenile rats submitted to chronic intermittent hypoxia (CIH). Male juvenile Wistar rats (20-21 days old) were submitted to CIH (6% O(2) for 40 s every 9 min, 8 h day(-1)) for 10 days while control rats were maintained in normoxia. Prior to CIH, baseline systolic arterial pressure (SAP), measured indirectly, was similar between groups (86 +/- 1 versus 87 +/- 1 mmHg). After exposure to CIH, SAP recorded directly was higher in the CIH (n = 28) than in the control group (n = 29; 131 +/- 3 versus 115 +/- 2 mmHg, P < 0.05). This higher SAP of CIH rats presented an augmented power of oscillatory components at low (10.05 +/- 0.91 versus 5.02 +/- 0.63 mmHg(2), P < 0.05) and high (respiratory-related) frequencies (12.42 +/- 2.46 versus 3.28 +/- 0.61 mmHg(2), P < 0.05) in comparison with control animals. In addition, rats exposed to CIH also exhibited an increased cardiac baroreflex gain (-3.11 +/- 0.08 versus -2.1 +/- 0.10 beats min(-1) mmHg(-1), P < 0.0001), associated with a shift to the right of the operating point, in comparison with control rats. Administration of hexamethonium (ganglionic blocker, i.v.), injected after losartan (angiotensin II type 1 receptor antagonist) and {[}beta-mercapto-beta,beta-cyclopenta-methylenepropionyl(1), O-Me-Tyr(2), Arg(8)]-vasopressin (vasopressin type 1a receptor antagonist), produced a larger depressor response in the CIH (n = 8) than in the control group (n = 9; -49 +/- 2 versus -39 +/- 2 mmHg, P < 0.05). Fifteen days after the cessation of exposure to CIH, the mean arterial pressure of CIH rats returned to normal levels. The data indicate that the sympathetic-mediated hypertension observed in conscious juvenile rats exposed to CIH is not secondary to a reduction in cardiac baroreflex gain and exhibits a higher respiratory modulation, indicating that an enhanced respiratory-sympathetic coupling seems to be the major factor contributing to hypertension in rats exposed to CIH. (AU)

• FAPESP's process: 04/03285-7 - Central mechanisms involved in the sympathoexcitation in response to hypoxia
• Grantee: Benedito Honorio Machado
• Support Opportunities: Research Projects - Thematic Grants