TACHYKININ NK1 RECEPTOR ANTAGONISTS ACT CENTRALLY TO INHIBIT EMESIS INDUCED BY THE CHEMOTHERAPEUTIC AGENT CISPLATIN IN FERRETS

These studies have compared the pharmacological profile of two non-pep tide human type neurokinin(1) (hNK(1)) receptor selective antagonists, L-741,671 and a quaternised compound L-743,310. In radioligand bindin g studies L-741,671 and L-743,310 had high affinity for ferret and clo ned hNK(1) receptors [K-i (nM) ferret 0.7 and 0.1; human 0.03 and 0.06 , respectively] but low affinity for rodent NK1 receptors [K-i (nM) 64 and 17, respectively] suggesting that ferret receptors have hNK(1)-li ke binding pharmacology. Studies in vivo showed that L-741,671 and L-7 43,310 had equivalent functional activity in the periphery (ID(50)s Of 1.6 and 2 mu g/kg i.v., respectively) as measured by inhibition of pl asma protein extravasation evoked in the oesophagus of guinea pigs by resiniferatoxin (7 nmol/kg i.v.). Using an in situ brain perfusion tec hnique in anaesthetised rats, L-741,671 was shown to be much more brai n penetrant than the quaternary compound L-743,310 which had an entry rate similar to the poorly brain penetrant plasma marker inulin. These compounds thus provided an opportunity to compare the anti-emetic eff ects of equi-active hNK(1) receptor antagonists with and without brain penetration to central NK1 receptor sites. When tested against cispla tin-induced emesis in ferrets, L-741,671 (0.3, 1 and 3 mg/kg i.v.) pro duced marked dose-dependent inhibition of retching and vomiting but L- 743,310 was inactive at 3 and 10 mg/kg i.v. In contrast, direct centra l injection of L-741,671 and L-743,310 (30 mu g) into the vicinity of the nucleus tractus solitarius or L-743,310 (200 mu g) intracisternall y was shown to inhibit retching and vomiting induced by i.v. cisplatin . L-741,671 and L-743,310 had equivalent functional activity, at the s ame dose, against cisplatin-induced emesis when injected centrally. Th ese observations indicated that had L-743,310 penetrated into the brai n after systemic administration it would have been active in the cispl atin-induced emesis assay and so show that brain penetration is essent ial for the anti-emetic action of systemically administered NK1 recept or antagonists. Copyright (C) 1996 Elsevier Science Ltd.