Endogenous digoxin-like immunoreactivity in blood is increased during prolonged strenuous exercise

Area of Science:

• Cardiology
• Exercise Physiology
• Biochemistry

Background:

• Digoxin-like immunoreactive factors (DLIFs) are endogenous substances with potential cardiotropic effects.
• The role of DLIFs during physiological stress, such as prolonged strenuous exercise, is not well understood.

Purpose of the Study:

• To investigate changes in serum DLIF levels during prolonged strenuous exercise.
• To explore the relationship between DLIF levels and cardiac function during exercise-induced fatigue.

Main Methods:

• Radioimmunoassay was used to measure total and loosely protein-bound DLIF in the serum of nine healthy subjects.
• Echocardiography was employed to assess cardiac function, including left ventricular fractional shortening (%FS) and mean velocity of circumferential fiber shortening (mVCF).
• Serum levels of nonesterified fatty acids and hydrocortisone were also analyzed.

Main Results:

• Serum DLIF levels increased by 72% (total) and 63% (loosely protein-bound) after three hours of exercise at 70% VO2max (p < 0.01).
• These elevations were not explained by changes in fatty acids or hydrocortisone.
• Cardiac function, measured by %FS and mVCF, decreased significantly post-exercise (p < 0.05).
• A significant negative correlation was found between %FS and serum DLIF levels (r = -0.680, p < 0.02).

Conclusions:

• Prolonged strenuous exercise leads to a significant increase in serum DLIF levels.
• Elevated DLIF levels correlate with cardiac dysfunction, suggesting a potential role in exercise-induced cardiac fatigue.
• Further research is warranted to elucidate the precise mechanisms and clinical implications of DLIFs in cardiovascular adaptation to exercise.