PITUITARY ADENYLATE CYCLASE-ACTIVATING PEPTIDE AND VASOACTIVE-INTESTINAL-PEPTIDE RECEPTOR EXPRESSION IN IMMORTALIZED LHRH NEURONS

The regulation of LHRH secretion is extraordinarily multifarious. To n o small extent, this insight has been gained through studies using the immortalized hypothalamic LHRH neuronal line, GT1-7. In the present s tudy, we examined these cells for potential expression of the receptor s for the related peptides PACAP and VIP. By means of reverse transcri ption-polymerase chain reaction (RT-PGR) with PACAP receptor-specific primers, in combination with restriction enzyme analysis and cDNA sequ encing, we were able to identify all PACAP-specific receptor splice va riant forms with variable degrees of expression. Of the two nonselecti ve VIP/PACAP receptors (i.e. VIP-R type I and II) only the latter isof orm was detected by RT-PCR. In view of these results, we sought to est ablish whether PACAP and VIP receptors are functional in GT1-7 cells. Cyclic AMP (cAMP) accumulation after addition of PACAP-38 (or PACAP-27 ) was dose-dependent with maximal 3-fold increases. VIP also elevated cAMP with a similar potency. Phosphatidylinositol (Pi) turnover was un affected by either PACAP or VIP. Acute LHRH secretion was stimulated e qually by nanomolar concentrations of both PACAP and VIP. These result s point to PACAP and VIP having direct actions via the VIP2R on cAMP s ignalling and LHRH release, in addition to the known effects of these peptides on pituitary functions.