Hyperosmolarity and cardiac function in chronic diabetic rat heart.

Area of Science:

• Cardiovascular Physiology
• Diabetic Pathophysiology
• Metabolic Regulation

Background:

• Serum hyperosmolarity is a hallmark of poorly controlled diabetes mellitus.
• Diabetic hearts exhibit altered responses to physiological challenges.

Purpose of the Study:

• To investigate the effects of hyperosmolar solutions on cardiac function in normal and diabetic rat hearts.
• To determine the role of extracellular calcium concentration in mediating these effects.

Main Methods:

• Isolated rat hearts from normal and diabetic models were perfused with varying osmolarity solutions (glucose, mannitol).
• Cardiac output and coronary conductance were measured under different extracellular calcium concentrations.
• Functional responses were compared between diabetic and normal hearts.

Main Results:

• Increased perfusate osmolarity reduced aortic output in both normal and diabetic hearts, but less severely in diabetic hearts.
• Diabetic hearts showed enhanced aortic output and prolonged performance under hyperosmolar conditions, especially at low extracellular calcium (1 mM).
• Coronary conductance improved in diabetic hearts with hyperosmolar perfusate, while it declined in normal hearts.

Conclusions:

• Hyperosmolar solutions exert a positive inotropic effect on diabetic rat hearts, particularly at physiological calcium levels.
• These findings suggest hyperosmolarity may enhance calcium availability in diabetic hearts, contributing to improved cardiac performance.
• The results indicate a potential adaptive mechanism in diabetic hearts responding to hyperosmolar stress.