Pressor and intestinal vascular bed responses to vasopressin after cholinergic blockade

Superior mesenteric arterial flow, aortic blood pressure, and heart rate were recorded, and plasma arginine vasopressin (AVP) concentrations were measured in conscious unrestrained cats during intravenous infusions of AVP (0.1-8.1 mU.kg-1. min-1). Responses to AVP were studied when autonomic nervous system (ANS) function remained intact and when the cholinergic limb of the system had been antagonized by methscopolamine nitrate (0.5 mg/kg) or by pirenzepine (60 micrograms/kg). Elevations in the circulating levels of AVP to approximately 30 and 600 fmol/ml in cats with intact ANS function were associated with decreases in superior mesenteric arterial conductance (SMAC, ml.min-1.kg-1.mmHg-1) of approximately 9 and 50%. The relationship between the dose of AVP and the decreases in SMAC for methscopolamine-treated cats was displaced slightly but significantly to the left of that for intact cats. The relationship between the dose of AVP and the increases in arterial pressure for methscopolamine-treated cats was also significantly displaced to the left of that for intact cats; however, the magnitude of the displacement was much greater than that for the dose-conductance relationship. In contrast to the findings with methscopolamine, pirenzepine did not significantly influence either the dose-conductance or dose-blood pressure response curves. These results are consistent with three conclusions. First, physiologically (less than 30 fmol/ml) and pathophysiologically (less than 600 fmol/ml) relevant concentrations of AVP are capable of inducing intestinal vasoconstriction, even in the presence of intact autonomic function. Second, the cholinergic limb of the autonomic nervous system plays a major role in buffering the vasopressor effects of AVP.(ABSTRACT TRUNCATED AT 250 WORDS)