Superior mesenteric arterial flow, arterial pressure, and heart rate were recorded, and plasma arginine-vasopressin (AVP) concentration was measured, during intravenous infusions of AVP (0.1-8.1 mU X kg-1 X min-1) in conscious unrestrained cats under two experimental situations--when autonomic function remained intact and, on other days, when it had been impaired by pretreatment of the animals with the ganglionic blocking agent pentolinium tartrate (2.5 mg X kg-1 and 0.125 mg X kg-1 X min-1). The dose-related increases in the plasma concentrations of AVP attained during the infusions of the peptide were similar under the two experimental situations. The curve expressing the relationship between the dose of AVP and the decrease in superior mesenteric arterial conductance (ml X min-1 X kg-1 X mm Hg-1) for when ganglia were blocked was similar to the curve for when autonomic function remained intact. Elevations in the circulating levels of the peptide within the physiological range (less than 30 fmol X ml-1) were associated with significant decreases in conductance, both when ganglia were blocked and when they were intact. In contrast to conductance, the curve expressing the relationship between the dose of AVP and the increase in arterial pressure for when ganglia were blocked was displaced markedly to the left when compared with the curve for when reflexes remained intact, even though the effect of ganglion blockade on pressor responses did not reach statistical significance with the two lowest doses of AVP.(ABSTRACT TRUNCATED AT 250 WORDS)