Pretreatment with vasodilator or V1-antagonist abolishes vasopressin withdrawal hypotension in spontaneously hypertensive rats.

In spontaneously hypertensive rats (SHR), the cessation of a 3-h intravenous infusion of arginine vasopressin (AVP, 8 mU/kg per min) resulted in a large and prolonged fall in arterial pressure (46 +/- 7.5 mmHg below basal levels). Pretreatment of SHR with the specific V1-receptor antagonist, [1-(beta-mercapto-beta, beta-cyclopentamethylene propionic acid), 2-(O-methyl)-tyrosine] AVP (d(CH2)5Tyr (Me)AVP, 8 micrograms/kg followed by 0.05 micrograms/kg per min) abolished the pressor response to AVP, and markedly reduced the subsequent hypotensive response following the cessation of the AVP infusion. The hypotensive response to AVP withdrawal was abolished also when phenylephrine hydrochloride (PE, 20 nmol/kg per min) elicited a blood pressure rise during the course of AVP infusion in rats with V1-receptor blockade. Finally, the concurrent administration of sodium nitroprusside (30 micrograms/kg per min) not only counteracted the pressure rise during AVP infusion, but also prevented the hypotensive response that normally accompanied the withdrawal of AVP. These findings demonstrate that neither V1-receptor activation nor blood pressure elevation alone was sufficient to generate a hypotensive response to the withdrawal of AVP; rather, both V1-receptor activation and a blood pressure elevation associated with the activation of these receptors were essential to the hypotensive response that followed the withdrawal of AVP in SHR.