Contrasting properties of bradykinin receptor subtypes mediating contractions of the rabbit and pig isolated iris sphincter pupillae preparation.

Bradykinin contracts both the pig and rabbit iris sphincter preparations. In the pig, the bradykinin antagonists Lys,Lys-[Hyp3, Thi5,8,D-Phe7]-BK and D-Arg-[Hyp3,Thi5,D-Tic7,Oic8]-BK (HOE140) inhibited responses with pKB estimates of 6.0 and 8.4, respectively. These affinities are markedly lower than in the rabbit preparation, suggesting that different receptors are present in each of the two species.