The role of GABA in the central regulation of AVP and ANP release and blood pressure due to angiotensin and carbachol, and central GABA release due to blood pressure changes.
To assess whether GABA given intracerebroventricularly (i.c.v.) affects vasopressin (AVP) and atrial natriuretic peptide (ANP) release and changes in blood pressure in response to i.c.v. angiotensin (AT II) and carbachol (CB), or whether changes in blood pressure affect GABA release in the brain, experiments were carried out. In experiment I (Ex I), GABA (100 micrograms) with AT II (50 ng) or CB (25 ng) was i.c.v. administered in conscious rats (n = 12). The same dose of AT II or CB alone also was administered without GABA (n = 12). In experiment II (Ex II), AT II (100 ng/kg per min) or nitropuruside (NP, 10 micrograms/kg per min) was intravenously (i.v.) infused and GABA release in the area adjacent to the paraventricular nucleus was determined, using the microdialysis method, in conscious rats (n = 12). In the experiments, mean arterial blood pressure (MABP), heart rate (HR), plasma AVP and/or ANP and plasma Na+ and K+ levels were measured. In Ex I, i.c.v. AT II increased plasma AVP and MABP without changes in HR and plasma ANP, but i.c.v. GABA never affected these responses. Icv CB also increased plasma AVP and MABP with decreased HR, but did not affect plasma ANP. Icv GABA abolished bradycardiac responses, but did not affect the others. In Ex II, the pressor response to i.v. AT II increased GABA release without apparent decreases in plasma AVP. However, the depressor response to NP produced decreases in GABA release with increased plasma AVP. These results shows that i.c.v. GABA did not affect AVP and pressor responses to i.c.v. AT II and CB, but changes in blood pressure modulates GABA release in the brain with changes in plasma AVP.
Second Department of Internal Medicine, Tohoku University School of Medicine, Sendai, Japan.
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T
Kimura
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Funyu
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M
Ohta
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Yamamoto
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Ota
M
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Shoji
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M
Inoue
K
K
Sato
K
K
Abe
D000804:Angiotensin II / Q000494:pharmacology; D000818:Animals; D001127:Arginine Vasopressin / Q000378:metabolism*; D009320:Atrial Natriuretic Factor / Q000378:metabolism*; D001794:Blood Pressure / Q000187:drug effects / Q000502:physiology*; D001921:Brain / Q000502:physiology*; D002217:Carbachol / Q000494:pharmacology; D006339:Heart Rate / Q000187:drug effects; D007276:Injections, Intraventricular; D008297:Male; D017551:Microdialysis; D009599:Nitroprusside / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology / Q000502:physiology*
D000804:Angiotensin II; D001127:Arginine Vasopressin; D009599:Nitroprusside; D005680:gamma-Aminobutyric Acid; D009320:Atrial Natriuretic Factor; D002217:Carbachol