Date Published: January 25, 2019
Publisher: Public Library of Science
Author(s): Ivan Ivic, Marta Balasko, Balazs D. Fulop, Hitoshi Hashimoto, Gabor Toth, Andrea Tamas, Tamas Juhasz, Akos Koller, Dora Reglodi, Margit Solymár, Sanbing Shen.
PACAP and VIP are closely related neuropeptides with wide distribution and potent effect in the vasculature. We previously reported vasomotor activity in peripheral vasculature of male wild type (WT) and PACAP-deficient (KO) mice. However, female vascular responses are still unexplored. We hypothesized that PACAP-like activity is maintained in female PACAP KO mice and the mechanism through which it is regulated differs from that of male PACAP KO animals.
We investigated the vasomotor effects of VIP and PACAP isoforms and their selective blockers in WT and PACAP KO female mice in carotid and femoral arteries. The expression and level of different PACAP receptors in the vessels were measured by RT-PCR and Western blot.
In both carotid and femoral arteries of WT mice, PACAP1-38, PACAP1-27 or VIP induced relaxation, without pronounced differences between them. Reduced relaxation was recorded only in the carotid arteries of KO mice as compared to their WT controls. The specific VPAC1R antagonist completely blocked the PACAP/VIP-induced relaxation in both arteries of all mice, while PAC1R antagonist affected relaxation only in their femoral arteries.
In female WT mice, VPAC1 receptors appear to play a dominant role in PACAP-induced vasorelaxation both in carotid and in femoral arteries. In the PACAP KO group PAC1R activation exerts vasorelaxation in the femoral arteries but in carotid arteries there is no significant effect of the activation of this receptor. In the background of this regional difference, decreased PAC1R and increased VPAC1R availability in the carotid arteries was found.
Pituitary adenylate cyclase-activating polypeptide (PACAP) is a member of vasoactive intestinal peptide (VIP)/secretin/glucagon superfamily [1–3]. PACAP exists in two biologically active forms, PACAP1-38 and PACAP1-27, sharing the same N-terminal 27 amino acids. PACAP1-27 shares 68% structure identity with VIP. The structure of PACAP1-38 is well conserved through evolution, suggesting the involvement of this neuropeptide in a diverse array of biological functions in many tissues and organs [4–7]. Some of these diverse biological functions include angiogenic capacity and vascular smooth muscle (SM) relaxation [7, 8]. The actions of PACAP are mediated via the PAC1 receptor (PAC1R) which is specific for PACAP and through VPAC1/VPAC2 receptors (VPAC1R and VPAC2R) which bind both PACAP and VIP with similar affinity [7, 9–11]. All receptors belong to the group of G protein-coupled receptors (secretin receptor family). Expression of PACAP isoforms and their receptors has been reported in the central nervous system [7, 12, 13] and in peripheral organs, including blood vessels [7, 14].
Our results showed that arteries of female mice reacted to administration of PACAP/VIP with vasorelaxation, similar to our previous observations in male mice . However, vessels of female mice show weaker relaxations compared to males. Females also seem to be less sensitive to the lack of PACAP than males. The main novel finding of the current study is, that in female mice, VPAC1 receptors appear to play a dominant role in PACAP-induced vasorelaxation both in carotid and in femoral arteries. While in the femoral arteries PAC1R activation exerts vasorelaxation, in carotid arteries of PACAP KO mice, there is no significant effect of the activation of this receptor.
This study is the first to show the relaxation effects of exogenous PACAP isoforms in peripheral arteries isolated from female WT and PACAP-deficient mice. These responses are more moderate than those of male mice. In female PACAP KO mice, carotid vasomotor responses to PACAP isoforms and VIP were reduced, but no differences were detected in the femoral arteries. In the background of this regional difference, decreased PAC1R and increased VPAC1R mediation of the carotid arteries were found. Our results also show, that in female mice, PACAP-induced vasorelaxation responses are mainly mediated by VPAC1R.