PITUITARY PROLACTIN MESSENGER-RIBONUCLEIC-ACID LEVELS IN INCUBATING AND LAYING HENS - EFFECTS OF MANIPULATING PLASMA-LEVELS OF VASOACTIVE INTESTINAL POLYPEPTIDE

Pituitary PRL messenger RNA levels in hens, measured by dot-blot hybridization, correlated directly with concentrations of plasma PRL, being 3-fold higher in incubating than in laying birds. Nest deprivation of incubating hens for 24 h caused a rapid decrease in both plasma PRL and pituitary PRL mRNA, which remained depressed thereafter. A single injection of vasoactive intestinal polypeptide (VIP) in laying hens resulted in an increase (P < 0.05) in pituitary PRL mRNA whereas passive immunoneutralization of VIP in incubating hens resulted in a decrease (P < 0.001) in pituitary PRL mRNA. The rapid decrease in pituitary PRL mRNA after nest deprivation or passive immunoneutralization of VIP was associated with a significant increase in pituitary PRL content, presumably a consequence of the decreased PRL secretion. In situ hybridization showed PRL mRNA to be localized in the cephalic lobe of the anterior pituitary gland in which most PRL cells, identified immunocytochemically, were found. Northern blotting studies showed that the pituitary gland contains a single 860 base(s) mature PRL mRNA transcript irrespective of physiological state or VIP manipulation. Both in situ and Northern hybridization studies confirmed that the amount of pituitary PRL mRNA was related directly to the concentration of plasma PRL. These observations are consistent with the view that in incubating hens hypothalamic VIP, in addition to acting as a PRL releasing hormone, also plays a major role in the regulation of the amount of PRL mRNA in the anterior pituitary gland.