Bradyzide is from a novel class of rodent-selective non-peptide B(2) bradykinin antagonists (1-(2-Nitrophenyl)thiosemicarbazides). Bradyzide has high affinity for the rodent B(2) receptor, displacing [(3)H]-bradykinin binding in NG108-15 cells and in Cos-7 cells expressing the rat receptor with K(I) values of 0.51+/-0.18 nM (n=3) and 0.89+/-0.27 nM (n=3), respectively. Bradyzide is a competitive antagonist, inhibiting B(2) receptor-induced (45)Ca efflux from NG108-15 cells with a pK(B) of 8.0+/-0.16 (n=5) and a Schild slope of 1.05. In the rat spinal cord and tail preparation, bradyzide inhibits bradykinin-induced ventral root depolarizations (IC(50) value; 1.6+/-0.05 nM (n=3)). Bradyzide is much less potent at the human than at the rodent B(2) receptor, displacing [(3)H]-bradykinin binding in human fibroblasts and in Cos-7 cells expressing the human B(2) receptor with K(I) values of 393+/-90 nM (n=3) and 772+/-144 nM (n=3), respectively. Bradyzide inhibits bradykinin-induced [(3)H]-inositol trisphosphate (IP(3)) formation with IC(50) values of 11.6+/-1.4 nM (n=3) at the rat and 2.4+/-0.3 microM (n=3) at the human receptor. Bradyzide does not interact with a range of other receptors, including human and rat B(1) bradykinin receptors. Bradyzide is orally available and blocks bradykinin-induced hypotension and plasma extravasation. Bradyzide shows long-lasting oral activity in rodent models of inflammatory hyperalgesia, reversing Freund's complete adjuvant (FCA)-induced mechanical hyperalgesia in the rat knee joint (ED(50), 0.84 micromol kg(-1); duration of action >4 h). It is equipotent with morphine and diclofenac, and 1000 times more potent than paracetamol, its maximal effect exceeding that of the non-steroidal anti-inflammatory drugs (NSAIDs). Bradyzide does not exhibit tolerance when administered over 6 days. In summary, bradyzide is a potent, orally active, antagonist of the B(2) bradykinin receptor, with selectivity for the rodent over the human receptor. British Journal of Pharmacology (2000) 129, 77 - 86