- Gastric inhibitory polypeptide is the major insulinotropic factor in K(ATP) null mice. Tsukiyama, K., Yamada, Y., Miyawaki, K., Hamasaki, A., Nagashima, K., Hosokawa, M., Fujimoto, S., Takahashi, A., Toyoda, K., Toyokuni, S., Oiso, Y., Seino, Y. Eur. J. Endocrinol. (2004)