Effect of phenylephrine injected into the nucleus tractus solitarius of Sprague-Dawley rats and spontaneously hypertensive rats.
In alpha-chloralose-anesthetized Sprague-Dawley (SD) rats with unilateral nucleus tractus solitarius (NTS) lesions, injection of the alpha(1)-adrenergic receptor agonist phenylephrine into the contralateral NTS dose-dependently increased arterial pressure (AP). Bunazosin (0.1 nmol) or prazosin (0.36 nmol), an alpha(1)-adrenergic receptor antagonist, also increased AP. When injected into the NTS, pre-treatment with phenylephrine (10 nmol) or both antagonists abolished the cardiovascular effects of glutamate and acetylcholine. In contrast, pre-treatment with prazosin or methylatropine did not alter the effect of phenylephrine. Phenylephrine (30 nmol) injected into the NTS abolished aortic depressor nerve (ADN) evoked-responses. The pressor effect of phenylephrine in the NTS was exaggerated in spontaneously hypertensive rats (SHR). These results suggest that when injected into the NTS, the effect of phenylephrine may be due to a baroreflex blockade resulting from direct modulatory actions or non-specific neuronal alterations rather than stimulating the alpha(1)-adrenergic receptor. Additionally, this effect is enhanced in SHR.
Second Department of Internal Medicine, Nihon University School of Medicine, Oyaguchi-Kamichou, Itabashi-ku, Tokyo, Japan.
Kazuyoshi
K
Tsukamoto
Satoru
S
Ito
Nobuhide
N
Katsunuma
Makoto
M
Hiratsuka
Yuichi
Y
Masubuchi
Takashi
T
Kanai
Takayuki
T
Kawabe
Yoshiharu
Y
Yajima
Katsuo
K
Kanmatsuse
D058646:Adrenergic alpha-1 Receptor Agonists; D058668:Adrenergic alpha-1 Receptor Antagonists; D000818:Animals; D001794:Blood Pressure / Q000187:drug effects / Q000502:physiology; D004305:Dose-Response Relationship, Drug; D006339:Heart Rate / Q000187:drug effects / Q000502:physiology; D008297:Male; D010656:Phenylephrine / Q000494:pharmacology*; D051381:Rats; D011918:Rats, Inbred SHR; D017207:Rats, Sprague-Dawley; D018340:Receptors, Adrenergic, alpha-1 / Q000502:physiology; D017552:Solitary Nucleus / Q000187:drug effects* / Q000502:physiology
D058646:Adrenergic alpha-1 Receptor Agonists; D058668:Adrenergic alpha-1 Receptor Antagonists; D018340:Receptors, Adrenergic, alpha-1; D010656:Phenylephrine