Ganglionic blockade in conscious dogs with chronic caval constriction.

Area of Science:

• Cardiovascular Physiology
• Renal Physiology
• Autonomic Nervous System Function

Background:

• Chronic thoracic inferior vena cava constriction reduces cardiac output and causes sodium retention.
• Arterial pressure is maintained in this model by increased total peripheral resistance.
• Sodium depletion also represents a low-output state with distinct physiological adaptations.

Purpose of the Study:

• To compare renal and hemodynamic responses to ganglionic blockade in conscious dogs with thoracic caval constriction.
• To contrast these responses with those in chronic sodium-deplete and normal sodium-replete dogs.
• To elucidate the role of the sympathetic nervous system in maintaining blood pressure in different physiological states.

Main Methods:

• Induction of chronic thoracic inferior vena cava constriction in dogs.
• Induction of chronic sodium depletion in dogs.
• Administration of ganglionic blockade in conscious sodium-replete, sodium-deplete, and caval constricted dogs.
• Measurement of arterial pressure, effective renal blood flow, creatinine clearance, and renal sodium excretion.

Main Results:

• Ganglionic blockade caused a significant fall in arterial pressure in caval constricted (20-30 mmHg) and sodium-deplete (20 mmHg) dogs.
• Normal sodium-replete dogs showed no change in blood pressure after ganglionic blockade.
• Renal blood flow and creatinine clearance remained unchanged; renal sodium excretion increased only in normal dogs.

Conclusions:

• The sympathetic nervous system plays a crucial role in maintaining arterial pressure in both sodium-deplete and caval constricted states.
• The adrenergic system's contribution to chronic sodium retention in these models was not evident.
• Reduced renal perfusion pressure post-blockade might have masked potential natriuretic responses.