Vasoactive intestinal peptide- and peptide histidine isoleucine amide-like immunoreactivity colocalize with vasopressin-like immunoreactivity in the canine hypothalamo-neurohypophysial neuronal system.

The distribution of vasoactive intestinal peptide (VIP) and peptide histidine isoleucine amide (PHI) was investigated in the canine hypothalamus by immunocytochemistry. VIP- and PHI-like immunoreactive neurons were detected in the magnocellular supraoptic and paraventricular nucleus. These magnocellular VIP- and PHI-producing neurons coexist with vasopressin-like immunoreactivity and send axons to the median eminence and neurohypophysis. These findings may serve as an anatomical basis for studying the function of VIP and PHI on pituitary hormone secretion.