Central norepinephrine pathways are involved in cardiovascular response to intracerebroventricular substance P.
OBJECTIVE
To study the role of norepinephrine system in the cardiovascular response to intracerebroventricular substance P (SP) in rabbit.


METHODS
SP was given intracerebroventricularly in anesthetized rabbits pretreated with the catecholaminergic neurotoxin, 6-hydroxydopamine (6-OHDA). The density and affinity of SP receptors on synaptosomal membranes of the hypothalamus and the ventral medulla of rabbits were determined by [125I]SP receptor assay. Arterial blood pressure and heart rate were recorded.


RESULTS
Intracerebroventricular (icv) pretreatment of rabbits with 6-OHDA, reduced norepinephrine in the hypothalamus (by 86.7 %) and in the ventral medulla (by 77.0 %) respectively. The pressor response and tachycardia of these rabbits to icv SP (3.55 nmol . kg-1) were attenuated. The density and the affinity of SP receptors in the hypothalamus and the ventral medulla of 6-OHDA-lesioned rabbits were decreased. The Bmax (pmol . g-1 protein) of SP receptors in hypothalamus and the ventral medulla are 108 +/- 5, 35.9 +/- 2.2 in control group, and 42 +/- 18, 20 +/- 5 in 6-OHDA-lesioned rabbits, respectively. Kd (nmol . L-1) of SP receptors in the two regions are 0.015 +/- 0.004, 0.014 +/- 0.006 in control group and 0.029 +/- 0.001, 0.015 +/- 0.003 in 6-OHDA group. There is a significant difference of Bmax (P < 0.01) and Kd (P < 0.01, P < 0.05) in both regions between 6-OHDA groups and control groups.


CONCLUSIONS
The results suggested that central norepinephrine pathways are involved in the cardiovascular response to icv SP.
Qian
H
H
Department of Physiology, Medical College of Southest University, Nanjing 210009, China. njqh@21cn.com
Yang
L P
LP
Wei
Z Y
ZY
Liu
A D
AD
Tian
H
H
Yang
S F
SF
D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D004298:Dopamine / Q000378:metabolism; D005260:Female; D006339:Heart Rate / Q000187:drug effects; D007031:Hypothalamus / Q000187:drug effects* / Q000378:metabolism; D007276:Injections, Intraventricular; D008297:Male; D008526:Medulla Oblongata / Q000187:drug effects / Q000378:metabolism; D009638:Norepinephrine / Q000378:metabolism*; D016627:Oxidopamine / Q000494:pharmacology; D011817:Rabbits; D018040:Receptors, Neurokinin-1 / Q000378:metabolism*; D013373:Substance P / Q000494:pharmacology*; D013574:Synaptosomes / Q000378:metabolism
D018040:Receptors, Neurokinin-1; D013373:Substance P; D016627:Oxidopamine; D004298:Dopamine; D009638:Norepinephrine