Cardiovascular effects of vasopressin following V-1 receptor blockade compared to effects of nitroglycerin

Studies to more clearly determine the mechanisms associated with arginine v asopressin (AVP)-induced vasodilation were performed in normal subjects and in quadriplegic subjects with impaired efferent sympathetic responses. Stu dies to compare the effects of AVP with the hemodynamic effects of nitrogly cerin, an agent that primarily affects venous capacitance vessels, were als o performed in normal subjects. Incremental infusions of AVP following Vi-r eceptor blockade resulted in equivalent reductions in systemic vascular res istance (SVRI) in normal and in quadriplegic subjects. However, there were major differences in the effect on mean arterial pressure (MAP), which was reduced in quadriplegic subjects but did not change in normal subjects. Thi s difference in MAP can be attributed to a difference in the magnitude of i ncrease in cardiac output (CI), which was twofold greater in normal than in quadriplegic subjects. These observations are consistent with AVP-induced vasodilation of arterial resistance vessels with reflex sympathetic enhance ment of CI and are clearly different from the hemodynamic effects of nitrog lycerin, i.e., reductions in INLAY, CI, and indexes of cardiac preload, wit h only minor changes in SVRI.