Redundant nature of the vasopressin and renin--angiotensin systems in the control of mesenteric resistance vessels of the conscious fasted cat.

[1-deaminopenicillamine, 4-valine, 8-D-arginine]Vasopressin (DPVDAVP), a specific antagonist of the pressor activity of vasopressin, and teprotide, a converting enzyme inhibitor, were infused intravenously in conscious, fasted (24-30 h) but not water-deprived cats which had been implanted previously with flow probes on their superior mesenteric arteries and with arterial and venous cannulae. Infusion of DPVDAVP (20 micrograms/min) alone or teprotide (1 mg over 5 min) alone caused only small and statistically nonsignificant changes in mesenteric conductance and arterial pressure. However, infusion of DPVDAVP during the plateau phase of the response to teprotide or, conversely, administration of teprotide during the plateau phase of the response to DPVDAVP caused large increases in mesenteric conductance and small but significant decreases in arterial pressure. The results are consistent with the hypothesis that vasopressin and angiotensin are redundant overlapping mechanisms that play a significant role in the control of the mesenteric resistance vessels of the conscious fasted cat; when one system is inhibited, the other compensates to maintain resistance.