Abstract |
We attempted to relate the signal pathway to the hypotension induced by arginine vasopressin (AVP) injection into the area postrema (AP) in urethane-anesthetized and ventilated rats with vagotomy. A femoral artery and vein were catheterized to measure the blood pressure (BP) and administer drugs, respectively. The rat was placed on a stereotaxic apparatus to expose the calamus sriptorius (CS) by craniostomy and maintained at normocapnia in hyperoxia. In protocol 1, hypotension evoked by AVP (3.0 x 10(-5) IU) microinjected into the AP 0.2 mm rostral to the CS of the midline was abolished by V(1A) antagonist, U73122 ( phospholipase C blocker), and BAPTA-AM (Ca(++) chelator), suggesting that an increasing intracellular Ca(++) is essential for AVP- induced hypotension. In protocol 2, AVP- induced hypotension was abolished by EGTA (extracellular Ca(++) chelator) and Ca(++) blockers such as nifedipine, nimodipine (L-types), and omega-conotoxin MVIIC (P/Q-type), but not by omega-conotoxin GVIA (N-type). In protocol 3, AVP- induced hypotension was blocked by calphostin C ( protein kinase C inhibitor) and mimicked by an increase in intracellular K(+) ions that was reversed by EGTA. Vehicle injections produced no changes in BP. In protocol 4, glutamate- induced hypotension was reversed by BAPTA-AM but not by EGTA or V(1A) antagonist. Our data suggest that AVP- induced hypotension depends on Ca(++) influx through a signal pathway from phospholipase C to protein kinase C which inactivates K(+) channels that may depolarize AP neurons to activate L- and P/Q-type Ca(++) channels. This may provide new insights into establishing a relationship between the signal pathway and physiological functions.
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Authors | Shu-Ju Yang, Ji-Chuu Hwang |
Journal | Brain research
(Brain Res)
Vol. 1163
Pg. 56-71
(Aug 13 2007)
ISSN: 0006-8993 [Print] Netherlands |
PMID | 17644073
(Publication Type: Journal Article, Research Support, Non-U.S. Gov't)
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Chemical References |
- Calcium Channel Blockers
- Chelating Agents
- Excitatory Amino Acid Antagonists
- Arginine Vasopressin
- 1,2-bis(2-aminophenoxy)ethane N,N,N',N'-tetraacetic acid acetoxymethyl ester
- Egtazic Acid
- Calcium
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Topics |
- Analysis of Variance
- Animals
- Area Postrema
(cytology)
- Arginine Vasopressin
(pharmacology)
- Blood Pressure
(drug effects)
- Calcium
(metabolism)
- Calcium Channel Blockers
(pharmacology)
- Chelating Agents
(pharmacology)
- Drug Administration Schedule
- Drug Interactions
- Egtazic Acid
(analogs & derivatives, pharmacology)
- Excitatory Amino Acid Antagonists
(pharmacology)
- Heart Rate
(drug effects)
- Hypertension
(chemically induced, metabolism, pathology, physiopathology)
- Male
- Microinjections
(methods)
- Neurons
(drug effects)
- Rats
- Rats, Wistar
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