title: Changes in vasopressin release and autonomic function induced by manipulating forebrain GABAergic signaling under euvolemia and hypovolemia in conscious rats.
abstract: The anteroventral third ventricular region (AV3V) is a pivotal area for osmotic responses and integration of autonomic functions. The purpose of this study was to investigate whether the gamma-aminobutyric acid (GABA)-ergic activity in the AV3V may be involved in the regulation of arginine vasopressin (AVP) secretion and related phenomena under the conditions with or without hypovolemia. Experiments were performed in conscious rats. We found that AV3V infusion with the GABA(A) receptor antagonist bicuculline in euvolemic rats caused prompt increases in plasma AVP, osmolality, glucose, arterial pressure and heart rate. The effects of the bicuculline infusion were abolished by prior infusion of a GABA(A) receptor agonist, muscimol. When repeated twice with a 10-min interval, removal of systemic blood (10 mL/kg body weight) lowered arterial pressure and enhanced plasma AVP, osmolality, glucose and angiotensin II. Muscimol infusion in the AV3V, but not in the cerebral ventricle, inhibited the responses of plasma AVP and glucose, despite having no effect in a sham hemorrhagic state. The inhibition of the AVP response by the muscimol infusion was also verified in rats given a combined stimulus of bleeding plus an osmotic load. In contrast, AV3V infusion with the GABA(B) receptor agonist baclofen tended to intensify the hemorrhagic responses of plasma AVP and glucose, despite its potency to prevent the hemorrhagic fall in arterial pressure. These results, taken together with our previous data, suggest that hypovolemic stimuli, like hyperosmotic stimuli, may promote AVP secretion by causing the inhibition of AV3V GABA(A)-ergic activity responsible for potentiation of glutamatergic activity.
authors.affiliation: Department of Homeostatic Regulation and Development, Niigata University Graduate School of Medical and Dental Sciences, Niigata City, Niigata 951-8510, Japan. kenbo@med.niigata-u.ac.jp
authors.forename: Ken'ichi
authors.initials: K
authors.lastname: Yamaguchi
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Hama
mesh_terms: D000818:Animals; D001127:Arginine Vasopressin / Q000097:blood / Q000378:metabolism / Q000502:physiology*; D001640:Bicuculline / Q000008:administration & dosage / Q000494:pharmacology*; D001794:Blood Pressure / Q000502:physiology; D058785:GABA-A Receptor Agonists / Q000494:pharmacology*; D058787:GABA-A Receptor Antagonists / Q000494:pharmacology*; D006339:Heart Rate / Q000502:physiology; D020896:Hypovolemia / Q000503:physiopathology; D008297:Male; D009118:Muscimol / Q000494:pharmacology*; D051381:Rats; D017208:Rats, Wistar; D020542:Third Ventricle / Q000378:metabolism / Q000502:physiology*; D005680:gamma-Aminobutyric Acid / Q000502:physiology*
chemical_list: D058785:GABA-A Receptor Agonists; D058787:GABA-A Receptor Antagonists; D001127:Arginine Vasopressin; D009118:Muscimol; D005680:gamma-Aminobutyric Acid; D001640:Bicuculline