Analogues of vasoactive intestinal peptide (VIP) contract the guinea-pig uterine artery but do not antagonize VIP-induced relaxations.

Guinea-pig vasoactive intestinal peptide (gpVIP-(1-28] in the concentration range 3 x 10(-9)-3 x 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.