Neurogenic and humoral factors maintaining arterial pressure in conscious dogs.

This study examined the contribution of each primary pressor system to resting arterial pressure and the ability of each to maintain pressure in the absence of the other systems in conscious dogs. In dogs with intact carotid sinus baroreflexes, ganglionic blockade (GB) reduced blood pressure by 13 +/- 3 mmHg, whereas blockade of the renin-angiotensin (RAS) and arginine vasopressin (AVP) systems did not significantly alter arterial pressure. After removal of the other two systems, the depressor response to blockade of the sympathetic nervous system (SNS) with hexamethonium and atropine was significantly augmented (-33 +/- 3 mmHg), whereas captopril (CAP) blockade of the RAS reduced pressure 14 +/- 4 mmHg, and AVP blockade decreased pressure 12 +/- 2 mmHg. In sinoaortic-denervated (SAD) dogs, the SNS exhibited a greater contribution (28 +/- 4 mmHg) to resting pressure compared with intact, and the role of the RAS (10 +/- 2 mmHg) was also augmented, whereas the effects of AVP blockade were unaltered. Effects of GB and CAP were unaltered after blockade of the other systems in SAD animals, whereas the depressor response to AVP antagonist (-13 +/- 2 mmHg) was significantly augmented. Results indicate the SNS is the primary pressor system in resting intact or SAD conscious dogs, whereas the RAS also contributes to resting blood pressure in SAD animals. The ability of the SNS alone to maintain arterial pressure after acute removal of the other systems is also significantly greater than that of AVP or the RAS.