CHRONIC INTRAVENOUS ADMINISTRATION OF V-1 ARGININE-VASOPRESSIN AGONIST RESULTS IN SUSTAINED HYPERTENSION

Despite the well-recognized vasoconstrictor and fluid-retaining action s of vasopressin, prolonged administration of arginine vasopressin (AV P) to normal animals or humans fails to produce sustained hypertension . The present study was performed to elucidate the role of the V-1 rec eptor in determining the ability of AVP to produce sustained hypertens ion. Conscious Sprague-Dawley rats with implanted catheters were infus ed with the selective V-1 agonist, [Phe(2),Ile(3), Orn(8)]vasopressin (2 ng.kg(-1).min(-1)), for 14 days in amounts that were acutely nonpre ssor. Blood pressure (MAP), heart rate (HR), body weight, and water in take (WI) were determined daily. Plasma AVP, plasma catecholamines nor epinephrine and epinephrine, plasma osmolality, and electrolyte concen tration were determined before and on days 1 and 7 of infusion. MAP in creased significantly by 10.4 +/- 4.5 mmHg on day 1 and rose to 22 +/- 5 mmHg above control by day 14 (transient decrease on days 6-9) and t hen fell to control levels after the infusion was stopped. HR did not change significantly. Plasma AVP immunoreactivity increased from 2.5 /- 0.3 to 10.9 +/- 2.1 pg/ml, whereas norepinephrine tended to fall on ly on clay 1, with epinephrine only slightly elevated on day 7. No evi dence of fluid retention was found, and rats lost sodium only on the f irst day of V-1 agonist infusion. Body weight increased throughout the study but was unrelated to the changes of MAP. We conclude that chron ic stimulation of V-1 receptors results in sustained hypertension in r ats.