Effects of Chronic Ethanol Ingestion on the Vasoactive Intestinal Peptide Receptor-Effector System From Rat Seminal Vesicle Membranes

Vasoactive intestinal peptide mRNA and immunoreactivity are decreased in fetal alcohol syndrome model

Vasoactive intestinal peptide (VIP) regulates growth in the early post-implantation embryo. Previous work has demonstrated that peptide agonists (SALLRSIPA and NAPVSIPQ) from downstream mediators that are regulated by VIP were able to prevent the alcohol-induced fetal death, growth restriction and microcephaly associated with fetal alcohol syndrome. Here we evaluated the role of VIP in this mouse model of fetal alcohol syndrome, to determine if fetal or maternal levels of VIP are altered. In addition, we evaluated whether peptide treatment would alter the effects of alcohol on VIP levels. Treatment groups included control, alcohol, and alcohol+peptides. VIP levels were measured with enzyme immunoassay [EIA] (Peninsula Laboratories, Belmont, CA). Quantitation of VIP expression was measured with rt-PCR using mimic cDNA primers. Embryo/decidual VIP levels were similar in control and alcohol-treated groups 6 h after treatment. However, in the embryo/deciduas at 12 and 24 h, VIP levels were below the EIA's detection limit in the alcohol-treated groups, and significantly lower than the control or peptide-pretreated groups (p<0.05). Maternal cortex VIP levels were undetectable and significantly lower in the alcohol-treated group than control or peptide+alcohol group at 6 and 12 h (p<0.001). VIP mRNA expression was quantitated in the embryo and deciduas, with a significant decline noted at 6 h to 58% of control levels (p=0.02). Pretreatment with the peptides attenuated the alcohol-induced decrease in VIP mRNA. These studies demonstrate that treatment with alcohol can decrease the expression and immunoreactivity of VIP in both maternal and fetal tissues. This alcohol-induced loss of a recognized regulator of embryonic growth and differentiation may contribute to the sequelae of toxicity observed in fetal alcohol syndrome.

Identification of G-proteins coupling to the vasoactive intestinal peptide receptor VPAC(1) using immunoaffinity chromatography: evidence for precoupling

VPAC(1) receptor subtype-specific G-protein interactions were identified using a strategy that exploits an essential initial signaling event, namely the functional and physical association of the receptor with G-protein. An immunoaffinity purification column was constructed using a previously characterized antibody that had been raised against the first extracellular loop of the VPAC(1) receptor. VPAC(1)/G-protein complexes were solubilized from membranes and copurified. Receptor and Galpha-proteins were detected in eluates using (125)I-VIP labeling and immunoblotting, respectively. Human VPAC(1) transfected in HEK293 cells couples to Gs but not Gi3, Gi1/2, or Gq. Rat VPAC(1) in brain membranes is coupled to Gs and Gi3. Rat VPAC(1) in lung membranes couples to Gs, Gi3, and Gq. Pretreatment of membranes with VIP increased the level of all G-proteins copurifying with VPAC(1). Immunoaffinity chromatography also revealed VPAC(1) receptor precoupling to G-protein in the absence of VIP pretreatment. This was confirmed using a cross-linking procedure to capture VIP receptor/G-protein complexes in the native membrane milieu prior to solubilization. Precoupling suggests that there is a significant basal level of VPAC(1) receptor activity especially in cells, such as some human malignant tumor cells, that express high levels of receptor.

VIP activates G(s) and G(i3) in rat alveolar macrophages and G(s) in HEK293 cells transfected with the human VPAC(1) receptor

We have characterized vasoactive intestinal peptide (VIP) receptor/G-protein coupling in rat alveolar macrophage (AM) membranes and find that pertussis toxin treatment and antisera against G(alphai3) and G(alphas) reduce high-affinity (125)I-VIP binding, indicating that both G(alphas) and G(alphai3) couple to the VIP-receptor. The predominant VIP-receptor subtype in AM is VPAC(1) and we examined the G-protein interactions of the human VPAC(1) that had been transfected into HEK293 cells. VPAC(1) has a molecular mass of 56 kDa; GTP analogs reduced (125)I-VIP binding to this protein demonstrating that high-affinity binding of VIP to the receptor requires coupling to G-protein. Functional VIP/VPAC(1)/G-protein complexes were captured by covalent cross-linking and analyzed by Western blotting. The transfected human VPAC(1) receptor in HEK293 was found to be coupled to G(alphas) but not G(alphai) or G(alphaq). Furthermore, pertussis toxin treatment had no effect on VPAC(1)/G-protein coupling in these cells. These observations suggest that the G-proteins activated by VPAC(1) may be dependent upon species and cell type.