Receptors for vasoactive intestinal peptide and pituitary adenylate cyclase-activating polypeptide in turkey cerebral cortex: characterization by [125I]-VIP binding and effects on cyclic AMP synthesis

Regulation of prolactin secretion in a nonphotoperiodic breeder, the zebra finch

“…Hypothalamic VIP is the primary PRL-stimulating agent in birds (Al Kahtane et al 2003;Zawilska et al 2004). VIP neurons located within the median eminence of the mediobasal hypothalamus release their product into the long portal vessels that stimulate the synthesis and release of PRL from lactotrophs in the anterior pituitary Youngren et al 1996a).…”

“…As the primary PRL-stimulating agent in birds, VIP also acts via specific G-protein coupled receptors VPAC 1 & VPAC 2 and appears to increase cAMP via the G s pathway, ultimately leading to an increase in PRL transcription in lactotrophs of the anterior pituitary (Al Kahtane et al 2003;Zawilska et al 2004). Levels of VIP in the systemic circulation remain relatively stable, but VIP in the hypothalamohypophyseal circulation is significantly higher than that measured systemically and generally parallels peripheral PRL levels (see Figure 1, below, modified from (Youngren et al 1996a).…”

“…Hypothalamic VIP-ir, mRNA content, and hypophyseal portal blood VIP levels are closely related to plasma PRL concentrations during turkey reproductive cycle (You et al 1995), and VIP increases PRL transcription rate, enhances PRL mRNA stability, and stimulates PRL secretion (Zawilska et al 2004). Reproductively inactive turkey hens have the lowest level of portal VIP, increasing during lay.…”

“…However, only one VIP receptor (VIP-R) type has been identified in birds Zawilska et al 2004). These receptors are G-protein coupled receptors linked to adenylate cyclase activity.…”

“…These receptors are G-protein coupled receptors linked to adenylate cyclase activity. They bind to pituitary adenylate cyclase activating peptide (PACAP) equally well as to VIP, and both are effective in stimulating cAMP production (Romano et al 2003;Zawilska et al 2004). A third PACAP receptor subtype not found in birds binds PACAP with greater affinity than VIP and activates PLC (Romano et al 2003).…”