| Research Abstract |
It has been known that central noradrenergic, glutamatergic and GABAergic neurons take part in the regulation of vasopressin (AVP) and blood pressure. However, it is still unknown whether changes in blood pressure, blood volume and plasma osmolality really affect the release of noradrenaline (NA), glutamate (GLU) and GABA in the brain. In order to clarify these problems, following experiments were carried out in conscious rats. The releases of NA,GLU and GABA in the paraventricular nucleus were determined using a microdialysis method with HPLC.In experiment I,angiotensin II (AT II ; 100ng/kg/min) or nitroprusside (NP ; 10mug/kg/min) was intravenously infused. AT II increased mean arterial pressure (MAP) and GABA release without apparent changes in NA release and plasma AVP.NP produced decreases in MAP and GABA release with an increase in plasma AVP,but no changes in NA release. In experiment II,hemorrhage (HEM ; 30% of blood volume) was performed. HEM decreased MAP and GABA release with an increase in plasma AVP,but did not change GLU release. In experiment III,Hypertonic saline (HS ; 2.5M NaCl) was infused intravenously. HS increased MAP,plasma osmolality and plasma AVP with a decrease in GABA release, but did not change GLU release. These results indicate that the microdialysis method may be useful to investigate the function and release of central neurotransmitters, and GABA in the hypothalamus may play important roles in the regulation of AVP release mediated through osmo-, baro- and volume-receptors.
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