Galanin stimulates the release of cholecystokinin from nerve fibres in the pituitary neurointermediate lobe.

Galanin (GAL), a 29 amino acid peptide, is present in magnocellular neurones in the paraventricular and supraoptic nuclei with projections to the neurohypophysis. The effect of GAL on the release of vasopressin, oxytocin and cholecystokinin (CCK) from rat neural lobes was investigated using an in vitro method. GAL in a concentration of 10(-6) M did not affect basal or K(+)-induced release of vasopressin or oxytocin. In contrast, GAL (10(-6) M) significantly stimulated basal and K(+)-stimulated release of CCK. Double-labelling immunofluorescence histochemistry of the neurohypophysis showed that GAL-immunoreactive (-IR) fibres co-contained vasopressin-like immunoreactivity (-LI), whereas the majority of oxytocin-IR fibres were CCK-IR. There was no evidence for colocalization of GAL with CCK or oxytocin. The data suggest a stimulatory role of GAL on CCK release via a paracrine effect on neighbouring oxytocin-CCK-containing nerve fibres.