[Changes in osmolarity of arterial blood in intensive muscle exercise]

Acute experiments in cats demonstrated that a prolonged rhythmic muscle contraction of four limbs induced by stimulation of transected motor nerve endings is concomitant with an increase in osmotic pressure of arterial and venous blood plasma both in blood vessels and in the heart. The increase in osmolarity is parallel to an increase in the minute volume of the heart, a fall in the arterial pressure and an enhanced blood flow through the exercising limbs. Muscle hyperemia is related to osmotic shifts in venous blood and the increased minute volume of the heart--to those in arterial blood. The osmotic factor seems to be involved in adaptation of the cardiovascular system to intensive physical exercise.