Autoradiographic localization of [ 125 I‐TYR 8 ]‐bradykinin receptor binding sites in the guinea pig spinal cord

The present study aimed to localize and characterize [ 125 I‐Tyr 8 ]‐BK binding sites in all major segments of the guinea pig spinal cord using in vitro quantitative receptor autoradiography. [ 125 I‐Tyr 8 ]‐BK specific binding sites were localized predominantly in superficial layers of the dorsal horn, with lamina II depicting the highest labelling. The density of specific binding in laminae I and III was moderate, whereas in other areas, i.e., laminae IV‐X, lower amounts of labelling were noticed. The B 2 receptor antagonists D‐Arg[Hyp 3 ,Thi 5 ,D‐Tic 7 ,Oic 8 ]‐BK (Hoe 140),D‐Arg[Hyp 3 ,D‐Phe 7 ,Leu 8 ]‐BK,Tyr 0 ,D‐Arg[Hyp 3 ,D‐Phe 7 ,Leu 8 ]‐BK, D‐Arg[Tyr 3 ,D‐Phe 7 ,Leu 8 ]‐BK, D‐Arg[Hyp 2 ,Thi 5.8 ,DPhe 7 ]‐BK, D‐Arg[Hyp 3 ,Leu 8 ]‐BK and D‐Arg[Hyp 3 ,Gly 6 ,Leu 8 ]‐BK as well a., unlabelled [Tyr 8 ]‐BK inhibited [ 125 1‐Tyr 8 ]‐BK binding with respective Ki values of 0.04, 12.4, 23.4, 34.5, 43.5, 33.5, 23.0, and 0.6 nM while B 1 related molecules (Tyr 0 , des‐Arg 10 ‐kallidin and [Leu 8 ]‐des‐Arg 9 ‐BK) did not significantly inhibit [ 125 I‐Tyr 8 ]‐BK binding up to micromolar concentrations. These results indicate that the specific [ 125 I‐Tyr 8 ]‐BK binding sites present in the guinea pig spinal cord belong to the B2 receptor subtype. The high density of B 2 binding sites in the substantia gelatinosa provides an anatomical evidence in favour of a role for BK as a modulator of nociceptive information. © 1993 Wiley‐Liss, Inc.