ANTERIOR-PITUITARY VASOACTIVE-INTESTINAL-PEPTIDE MESSENGER-RNA IS COLOCALIZED WITH PROLACTIN MESSENGER-RNA IN HYPEROESTROGENISED RATS

It is well established that oestrogens can stimulate prolactin (PRL) s ecretion as well as the expression of the vasoactive intestinal peptid e (VIP) gene whose product is also a potent PRL secretagogue. Previous evidence has supported both an autocrine and a paracrine role for pit uitary VIP in PRL release in vitro; however, the cellular origin of VI P in pituitary tissue still remains poorly defined. In these studies, we have demonstrated by in situ hybridisation that VIP RNA is detected in the anterior pituitaries of chronically hyperoestrogenised rats, b ut not in those of untreated animals. Using a double-probe labelling p rocedure, VIP RNA has been shown to be present in a subpopulation of P RL-producing cells, while colocalisation of VIP and GH RNA was not obs erved. VIP gene expression in the rat anterior pituitary gland was cha racterised by the presence of two alternatively polyadenylated transcr ipts, 1.7 kb and 1.0 kb in size. We have generated a probe specific fo r the 1.7 kb transcript and double-labelling studies also showed defin ite colocalisation with PRL mRNA. Our results demonstrating the presen ce of VIP RNA in PRL-producing cells thus suggest that VIP may play an autocrine role in PRL hypersecretion under conditions of oestrogen-in duced hyperplasia.