Chronic but not acute exposure to stress is associated with hypothalamic vasoactive intestinal polypeptide (VIP)...

The influence of stress on hypothalamic VIP release into the pituitary portal blood has not been assessed at present despite the fact that this peptide has been implicated in the control of several pituitary hormones and especially in the release of prolactin (PRL) caused by stress. In the present work the effect of stress on the in vivo release of VIP into the pituitary portal blood of male rats was evaluated by means of push-pull perfusion (PPP) of median eminence (EM). VIP content in the PPP liquid was successfully measured and their levels agree well with pituitary portal blood levels measured by other authors. Whereas plasma PRL levels strongly increased during acute immobilization (IMO), no changes in VIP secretion into the ME were observed. VIP release into the ME was also unaffected by exposure to ether. In contrast, in chronically immobilized rats a significant increase in VIP release into the ME was obtained in response to acute IMO. The present data argue against a major role of hypothalamic VIP in PRL release caused by acute stress and show that chronic stress qualitatively alters the signal of hypothalamic VIP to the pituitary.