Effect of vasopressin antagonist d(CH2)5Tyr(Et)VAVP on plasma arginine vasopressin level after osmotic stimulus.

The effect of the vasopressin antagonist d(CH2)5Tyr(Et)VAVP on the immunoreactive arginine vasopressin (AVP) level in plasma was studied in rats after osmotic stimulus. The blood samples were obtained from the eye plexus. An increased AVP level (193.2 +/- 70.0; control: 30.5 +/- 4.3 pmol/l) was detected after the administration of hypertonic NaCl solution. A much higher elevation of AVP level (1180.9 +/- 181.0 pmol/l) was observed when treatment with the antagonist was applied before the osmotic stimulus. The results indicate that this compound exerts a biological effect as a vasopressin receptor blocking agent through a mechanism of competitive antagonism.