Circulatory effects evoded by 'physiological' increases of arterial osmolality

Area of Science:

• Physiology
• Cardiovascular Science
• Hemodynamics

Background:

• Arterial hyperosmolality can occur during physiological stress like heavy exercise and hemorrhage.
• Understanding the cardiovascular responses to hyperosmolality is crucial for comprehending these stress states.

Purpose of the Study:

• To investigate the effects of moderate arterial hyperosmolality on vascular resistance in various tissues.
• To determine the role of sympathectomy and beta-adrenoceptor blockade in these responses.
• To analyze the impact on systemic hemodynamics, including blood pressure, heart rate, stroke volume, and cardiac output.

Main Methods:

• Anesthetized cats underwent short-term intravenous infusion of hypertonic solution to induce moderate arterial hyperosmolality (+20 mOsm/kg H2O).
• Vascular resistance was measured in the skin, skeletal muscle, intestine, and kidney.
• Experiments were conducted before and after regional sympathectomy, and with beta-adrenoceptor blockade.

Main Results:

• Vascular resistance decreased in all four analyzed regions (skin, skeletal muscle, intestine, kidney) in response to hyperosmolality.
• These decreases in vascular resistance were observed both before and after regional sympathectomy.
• Beta-adrenoceptor blockade did not significantly alter the effects of hyperosmolality on vascular resistance.
• Arterial blood pressure increased during hypertonic infusion despite decreased vascular resistance and unchanged heart rate, indicating increased stroke volume and cardiac output.

Conclusions:

• Blood-borne hyperosmolality causes vasodilation in multiple vascular beds.
• The cardiovascular adjustments to hyperosmolality are largely independent of sympathetic nervous system activity and beta-adrenergic pathways.
• Hyperosmolality may be a significant contributing factor to the cardiovascular adjustments observed during heavy exercise and hemorrhage.