Effect of caerulein on plasma corticosterone concentration in the rat

Intraperitoneal injection of caerulein produced a pronounced increase in plasma corticosterone levels in intact rats. Since this effect was not observed in hypophysectomized rats, it is assumed that the peptide does not affect the adrenal gland directly. Intracerebroventricular injection of caerulein was also ineffective in stimulating corticosterone secretion, and $\text{in vitro}$ experiments for ACTH release indicated that caerulein could not affect pituitary tissue itself. The fact that the effect of caerulein disappeared after subdiaphragmatical vagotomy suggests that the action site is at a peripheral level, but not in the central nervous system.