Hemodynamic effects elicited by stimulation of the nucleus tractus solitarii.
Microinjection of the excitatory amino acid L-glutamate into the nucleus tractus solitarii (NTS) elicits decreases in arterial pressure and heart rate. In the present study, we sought to determine the regional hemodynamic effects that were correlated with changes in arterial pressure and heart rate produced by stimulation of the NTS. In anesthetized rats, blood flow in the renal (RBF), superior mesenteric (MBF), and hindquarter (HBF) vascular beds was measured by pulsed Doppler flowmeters. Relative vascular resistances (RVR, MVR, and HVR) were calculated by dividing mean arterial pressure (mm Hg) by the Doppler shift (kHz). Microinjection of L-glutamate into the NTS caused rapid, transient, dose-related decreases in mean arterial pressure and heart rate. MVR and RVR were minimally changed immediately after injections, but both demonstrated delayed dilatation. In contrast, HVR fell immediately but demonstrated delayed constriction. Identical changes occurred in intact rats and in those with interruption of the baroreflex by sinoaortic denervation. Ganglionic blockade with hexamethonium abolished virtually all L-glutamate-induced responses. This study suggests that NTS neurons exert differential effects on renal, mesenteric, and hindquarter vascular beds and that glutamate-induced regional hemodynamic changes are mediated predominantly through autonomic pathways.
Yin
M
M
Department of Neurology, University of Iowa College of Medicine, Iowa City 52242.
Lee
C C
CC
Ohta
H
H
Talman
W T
WT
D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D005971:Glutamates / Q000008:administration & dosage / Q000494:pharmacology*; D018698:Glutamic Acid; D006339:Heart Rate / Q000187:drug effects; D006439:Hemodynamics / Q000187:drug effects*; D018738:Hexamethonium; D006584:Hexamethonium Compounds / Q000494:pharmacology; D006614:Hindlimb / Q000294:innervation; D007668:Kidney / Q000098:blood supply; D008297:Male; D008526:Medulla Oblongata / Q000187:drug effects / Q000502:physiology*; D008845:Microinjections; D051381:Rats; D017207:Rats, Sprague-Dawley; D012039:Regional Blood Flow / Q000187:drug effects; D012079:Renal Circulation / Q000187:drug effects; D013152:Splanchnic Circulation / Q000187:drug effects; D014655:Vascular Resistance / Q000187:drug effects
D005971:Glutamates; D006584:Hexamethonium Compounds; D018738:Hexamethonium; D018698:Glutamic Acid