Osmotic stimuli attenuate vasoactive intestinal peptide gene expression in the rat anterior pituitary gland.

Studies on vasoactive intestinal peptide (VIP) in the anterior pituitary gland have shown that it is synthesized locally, physiologically regulated, and may act as a paracrine/autocrine factor. We have now investigated the regulation of anterior pituitary VIP gene expression in rats during osmotic stimulation. Both salt-loading and dehydration resulted in a progressive and marked reduction in VIP mRNA levels as determined by Northern analysis, to 10% of control levels at 14 days of salt-loading. The 1.7 and 1.0 kb VIP RNA transcripts were equally affected. Since anterior pituitary VIP is partially localized in lactotrophs we also measured prolactin (PRL) mRNA levels. In contrast to VIP, PRL mRNA levels were increased during both osmotic paradigms, the mRNA levels being significantly raised after 5 days of salt-loading to 130% of controls. Further experiments, conducted to examine the mechanism by which VIP gene expression is down-regulated during osmotic stimulation, demonstrated that dopamine and angiotensin II do not appear to be involved. The results show dissociated regulation of VIP and PRL during osmotic stimulation and provide suggestive evidence of a role for anterior pituitary VIP in the animal's osmoregulatory responses. VIP may therefore be a paracrine factor with diverse functional roles.