Cholecystokinin octapeptide in the rat hypothalamo-neurohypophysial system.

Gastrin-cholecystokinin (CCK)-like immunoreactivity has been visualized by immunohistochemistry in the vasopressin-oxytocin neurosecretory system comprising the posterior lobe of the pituitary, the supraoptic and paraventricular nuclei of the hypothalamus. This CCK-like substance has not been chemically identified in the rat, but has been reported to be gastrin 17 in the swine pituitary. We report here that this CCK-like immunoreactive substance co-chromatographs with CCK8 sulphate on Sephadex G-50 and two HPLC chromatographic systems. No gastrin 17 was detected in rat pituitary or brain. We further report that about 60% of the CCK in posterior lobe originates in cell bodies in the paraventricular nucleus of the hypothalamus. The CCK content of posterior pituitary is dramatically decreased by physiological perturbations which stimulate vasopressin or oxytocin release. We propose that CCK may either be co-secreted with vasopressin and oxytocin to act on peripheral targets or may be involved in the regulation of vasopressin or oxytocin neurosecretion.