Effect of dietary sodium intake on the responses to bicuculline in the paraventricular nucleus of rats.
The tachycardic, pressor, and renal sympathoexcitatory responses produced by administration of the gamma-aminobutyric acid antagonist bicuculline into the paraventricular nucleus of the rat are attenuated by the administration of losartan, an angiotensin II type 1 receptor antagonist, into the ipsilateral rostroventrolateral medulla. Therefore, excitatory synaptic inputs to pressor neurons in the rostroventrolateral medulla that arise from activation of the paraventricular nucleus are mediated predominantly by the action of angiotensin II on angiotensin II type 1 receptors. To examine whether such responses are influenced by physiological changes in the activity of the renin-angiotensin system, we measured heart rate, arterial pressure, and renal sympathetic nerve activity responses to the administration of bicuculline in the paraventricular nucleus in normal rats that were fed low-, normal-, and high-sodium diets and in rats with congestive heart failure. The rank order of both plasma renin activity and renal sympathoexcitatory responses was congestive heart failure>low-sodium diet>normal-sodium diet>high-sodium diet. The rank order of pressor and tachycardic responses exhibited a similar trend, but the differences between the groups were smaller and not statistically significant. The results indicate that the renal sympathoexcitatory responses to activation of the paraventricular nucleus are modulated by physiological alterations in the activity of the renin-angiotensin system.
DiBona
G F
GF
Departments of Internal Medicine and Physiology, University of Iowa College of Medicine, and Veterans Administration Medical Center, Iowa City, IO 52242, USA. gerald-dibona@uiowa.edu
Jones
S Y
SY
D000818:Animals; D001640:Bicuculline / Q000494:pharmacology*; D001794:Blood Pressure / Q000187:drug effects; D018756:GABA Antagonists / Q000494:pharmacology*; D006333:Heart Failure / Q000503:physiopathology; D006339:Heart Rate / Q000187:drug effects; D007668:Kidney / Q000294:innervation; D007700:Kinetics; D008297:Male; D010286:Paraventricular Hypothalamic Nucleus / Q000187:drug effects*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012084:Renin-Angiotensin System; D012964:Sodium / Q000378:metabolism*; D013564:Sympathetic Nervous System / Q000187:drug effects
D018756:GABA Antagonists; D012964:Sodium; D001640:Bicuculline