Pressor responses to vasopressin in pigs and sheep with DOCA hypertension

Pressor responses to vasopressin were determined in pigs and sheep during three experimental periods: 1) before deoxycorticosterone acetate (DOCA) treatment, 2) 21 days after DOCA implantation (100 mg/kg) when a stable hypertension had developed, and 3) after reversal of the hypertension by removing the implant in the sheep or by decreasing the dietary sodium intake in the pigs. The infusion of lysine (LVP) or arginine (AVP) vasopressin into pigs and sheep, respectively, resulted in dose-dependent increases in plasma vasopressin concentration. The levels of plasma LVP or AVP achieved by these infusions were not altered in any of the experimental periods. The administration of vasopressin resulted in dose-dependent increases in mean arterial blood pressure. However, pigs required five times more LVP than sheep required AVP to achieve similar pressor responses. The pressor responsiveness to vasopressin was attenuated when either species was made hypertensive. This effect was reversed when normal blood pressure was restored by reducing sodium intake in the pigs or by removing the DOCA implant from the sheep. These data establish that an increased pressor response to vasopressin does not contribute to DOCA hypertension in pigs or sheep.