Which of these substances is known to enhance endurance by increasing red blood cell production?

The substance known to enhance endurance by increasing red blood cell production is blood doping. This practice involves various techniques to increase the number of red blood cells in the bloodstream, thereby improving the body's ability to transport oxygen to muscles during prolonged physical activity.

By enhancing oxygen delivery, athletes can significantly improve their aerobic capacity and endurance, resulting in better performance in endurance sports. Blood doping can take various forms, including the transfusion of additional red blood cells or the use of agents that stimulate the body's production of red blood cells, like erythropoietin (EPO).

In contrast, other substances mentioned do not primarily function to enhance endurance through red blood cell production. Androstenedione and tetrahydrogestrione are both anabolic steroids that may promote muscle growth and recovery but do not specifically increase red blood cell production significantly. Human growth hormone can aid in recovery and muscle building, but its direct relationship with red blood cell production and enhancement of endurance is not as prominent as that of blood doping techniques.