Changes in the Number and Affinity of Erythrocyte Insulin Receptors in Prolonged Walking and Running

The number and affinity of erythrocyte insulin receptors in high and low concentrations of insulin were studied hourly in seven healthy 35-year-old, moderately trained men in 2–3 hours of walking and running, and for 3 hours after wards. Similar measurements were made on a control day during 5 hours with no exercise. The walking lasted for 3 hours at a mean heart rate of 116 \pm 3 beats/min(\pm SE), and running for 135 \pm 7 minutes at a heart rate of 153 \pm 3 beats/min. The insulin receptor number increased in both exercises, with the increase during the first hour being greater in running than in walking. The high-affinity component of the receptor was unchanged in exercise. The low-affinity component decreased in both walking and running. Blood glucose levels did not change in exercise. Serum insulin and C-peptide decreased during the first hour in both exercises and remained decreased to the end of the recovery. Plasma glucagon increased more in running than in walking. It is suggested that blood glucose and insulin are not the only regulators of erythrocyte insulin receptors in prolonged physical exercise.