THE ROLES OF GABA IN THE CENTRAL REGULATION OF AVP AND ANP RELEASE AND BLOOD-PRESSURE IN HYPERTONIC SALINE INFUSION AND HEMORRHAGE

In order to assess the central effects of gamma-aminobutiric acid (GAB A) on arginine vasopressin (AVP) and atrial natriuretic peptide (ANP) release and cardiovascular function, the following two experiments (Ex p) were carried out in conscious rats (n = 24). Experiment I: GABA (10 mug/kg - min) was intracerebroventricularly (i.cv.) administered into conscious rats receiving an intravenous (iv.) infusion of 2.5 M NaCl, and the vehicle alone was i.cv. administered under i.v. 2.5 M NaCl in the control group. Experiment II: GABA (12 mug/kg . min) was infused i.c.v. in conscious rats during hemorrhage (1.6% of BW) and the vehicl e alone was i.cv. administered during hemorrhage in the control study. In Experiment I, plasma AVP and ANP and mean arterial blood pressure (MABP) increased in response to 2.5 M NaCl, but heart rate (HR) slight ly decreased. I.C.V. GABA attenuated the AVP and ANP responses, but di d not affect MABP and HR. In Experiment II, plasma AVP increased due t o decreases in MABP induced by hemorrhage, but plasma ANP and HR never changed. I.C.V. GABA did not affect plasma AVP and ANP, MABP and HR. These results show that i.c.v. GABA has an inhibitory effect on AVP an d ANP release in response to hypertonic NaCl, but not to hemorrhage, b ut never affected hypertonic NaCl-induced increases in blood pressure.