Ki: 0.19±0.04 μM (histamine H ₁ receptor)

ReN 1869 is a highly selective tricyclic antihistamine that shows functional histamine H ₁ receptor antagonism. Binding studies with radioactively labelled ReN 1869 reveals high affinity only for the histamine H ₁ receptor in addition to some affinity for a sigma site. ReN 1869 is profiled for activity at 10 μM at various receptors, transporters, enzymes and ion channels. ReN 1869 only demonstrates affinity to the histamine H1 receptor (guinea pig brain, [ ³ H]pyrilamine) with a K _i of 0.19±0.04 μM and the non-selective σ site [guinea pig brain, [ ³ H]1,3-di-tolylguanidine (DTG)] with a K _i of 0.45 μM. ReN 1869 dose-dependently reduces the responses with IC ₅₀ of 1.70±0.002 μM.

The in vivo binding of [ ³ H]Mepyramine to mouse spinal cord and cerebellar histamine H ₁ receptors is dose-dependently inhibited by ReN 1869. ReN 1869 (in doses as low as 10 μg/kg i.p.) significantly inhibits the histamine-evoked paw edema. The ED ₅₀ is approximately 300 μg/kg. Interestingly, even a high dose of Mepyramine (10 mg/kg) is unable to inhibit significantly this type of edema (0.29±0.06 versus 0.34±0.05 in controls, n=7).ReN 1869 (1 mg/kg s.c.) is administered 30 min before paw injection with carrageenan and has no effect on the development of the paw edema. Dexamethasone (1 mg/kg s.c.) is given 1 h before carrageenan and expectedly diminished the edema. This effect is not affected by the simultaneous administration of 1 mg/kg ReN 1869.