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NEUROHUMORAL CONTROL OF CARDIOVASCULAR FUNCTION

Role of the arterial baroreflex in 5-HT_1A receptor agonist-mediated sympathoexcitation following hypotensive hemorrhage

Department of Pharmacology and Experimental Therapeutics, Loyola University Chicago, Stritch School of Medicine, Maywood, Illinois

Submitted 14 September 2005 ; accepted in final form 24 December 2005

5-HT_1A-receptor agonists rapidly restore blood pressure and sympathetic activity in conscious rats subjected to hypotensive hemorrhage. 5-HT_1A-receptor activation has also been shown to produce a robust increase in baroreceptor-dependent, pulse-synchronous firing of cardiac sympathetic nerves in anesthetized cats. To determine whether 5-HT_1A-receptor agonists reverse hemorrhage-induced suppression of sympathetic activity through facilitation of the arterial baroreflex, the effects of the 5-HT_1A-receptor agonist, 8-OH-DPAT, were assessed in male Sprague-Dawley rats subjected to sinoaortic baroreceptor denervation and subsequent hypotensive hemorrhage. 8-OH-DPAT produced rapid pressor and sympathoexcitatory responses in hemorrhaged animals that were attenuated, but not blocked, by sinoaortic denervation (SAD) (+49 ± 4 vs. +37 ± 4 mmHg; +165 ± 30 vs. +92 ± 24% baseline, P < 0.01). Spectral analysis of sympathetic activity showed that SAD abolished the 8-hydroxy-2-(di-n-propylamino)-tetralin (8-OH-DPAT)-mediated increases in pulse-synchronous (13 ± 1 vs. 5 ± 1% total power for intact vs. SAD rats, P < 0.01) and Mayer wave-related bursting (18 ± 3 vs. 8 ± 1% total power, P < 0.05). However, 8-OH-DPAT continued to increase total power (+72 ± 22 vs. –63 ± 7% prehemorrhage total power, P < 0.05) and power at the respiratory frequency (35 ± 2 vs. 25 ± 4% total power) in SAD animals. These data indicate that full expression of the sympathoexcitatory effect of 8-OH-DPAT requires a functional arterial baroreflex. However, a portion of the effect is due to activation of arterial baroreflex-independent sympathetic pathways.

spectral analysis; 8-hydroxy-2-(di-n-propylamino)-tetralin; Mayer wave; respiration

This article has been cited by other articles:

				J. Ahlgren, K. Porter, and L. F. Hayward Hemodynamic responses and c-Fos changes associated with hypotensive hemorrhage: standardizing a protocol for severe hemorrhage in conscious rats Am J Physiol Regulatory Integrative Comp Physiol, May 1, 2007; 292(5): R1862 - R1871. [Abstract] [Full Text] [PDF]