Fig. 3

Nitric oxide-dependent blood flow across the mammary gland. Nitric oxide, which is synthesized from arginine in endothelial cells of the blood vessel, increases the rate of blood flow across the mammary gland by stimulating the generation of cGMP from GTP. cGMP activates protein kinase G in smooth muscle cells to promote their relaxation. Uptake of a nutrient by the mammary gland is calculated, based on the Fick principle, as the difference in the concentration of the nutrient between arterial and veinous blood × the rate of blood flow. A = concentration of a nutrient in arterial blood; V = concentration of the nutrient in venous blood