| Summary: | Introduction. The present study was designed to determine the effects of selective antagonists of angiotensin II receptor types AT 1 and AT 2 on the flow of urine and sodium excretion induced by arginine vasopressin (AVP). Materials and methods. To this end, the drugs were microinjected into the medial septal area (MSA) of the brains of male Holtzman rats. Intravenous infusion of hypotonic saline was used to promote urinary flow, which was collected for one hour. Results. MSA microinjections of AVP decreased the urinary flow and increased sodium excretion in a dose-dependent manner. Microinjection into MSA of an AT 2 antagonist (PD-123319) had a significantly greater effect than with an AT 1 antagonist (losartan) in increasing urinary flow and decreasing sodium excretion. These effects were more pronounced when both antagonists were injected together, before the AVP. Conclusions. These results indicate that MSA AT 1 and AT 2 receptors act synergistically in the regulation of urine and sodium excretion induced by AVP.
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