Guinea-pig vasoactive intestinal peptide (gpVIP-(1-28)) in the concentration range 3 ?? 10-9-3 ?? 10-7 mol. 1-1 relaxed precontracted segments of the guinea-pig uterine artery. Porcine VIP-(10-28) (pVIP-(10-28)), [4-Cl-D-Phe6, Leu17]VIP, or [N-Ac-Tyr1, D-Phe2]GRF-(1-29)-NH2 did not antagonize VIP-induced relaxations of the artery, but high concentrations of the two VIP analogues produced large, transient contractions of the artery. In some preparations 10-5 mol ?? 1-1 gpVIP-(1-28) also caused transient arterial contractions. These data indicate the presence of two distinct receptors for VIP on the guinea-pig uterine artery, mediating opposite effects on vascular tone. ?? 1989.
Morris, J. L., & Murphy, R. (1989). Analogues of vasoactive intestinal peptide (VIP) contract the guinea-pig uterine artery but do not antagonize VIP-induced relaxations. European Journal of Pharmacology, 162(2), 375–379. https://doi.org/10.1016/0014-2999(89)90303-8