Nitric oxide synthase activities in mammalian parotid and submandibular salivary glands

Nitric oxide is important as a physiological messenger molecule in various organs and cells. It is synthesized from the amino acid l-arginine by nitric oxide synthase. Here, the specific activities of nitric oxide synthase in the cytosolic fractions of rabbit, bovine, mice, rat, and guinea-pig parotid and submandibular glands were compared. Marked specific activities were detected in the rabbit and bovine parotid and submandibular glands and in the parotid of mice. The activity in rabbit parotid was highest and was similar to that in rabbit brain. The significant activities in the salivary glands were completely blocked in the absence of Ca2+ or the presence of a calmodulin inhibitor. These findings suggest that the rabbit parotid glands are useful for studying the regulation of nitric oxide generation by Ca2+/calmodulin-dependent nitric oxide synthase in salivary glands.