Table 1. The activitiesa of histamine receptor ligands across four receptors K_d/K_i (nM).

	Ileumb	Atriumb	Hc	Hc
	H1	H2	H3	H4
Mepyramine (pyrilamine)	0.4	5,200	>10,000	>10,000
Diphenhydramine	1.0	>10,000	>10,000	>10,000
Cimetidine	>10,000	800	>10,000	>10,000
Ranitidine	>10,000	200	>10,000	>10,000
Dimaprit	>10,000	1,100	825	377
Impromidine	3400	63	67	12
Thioperamide	>10,000	>10,000	60d	27
Clobenpropit	>10,000	>10,000	0.6	12
UCL 2138e			11f	>10,000
R-(α)-methylhistamine			0.7	146
Imetit			0.3	2.7
JNJ 7777120	>10,000c	>10,000g	5125	4.1
Histamine			5.4	8.1

^aData from Hough (2001).

^bGuinea-pig.

^cRecombinant human receptor.

^dLigneau et al. (2000).

^eN-(3-p-cyanophenoxypropyl)piperidine, ED₅₀ (p.o., H₃, mouse)=0.2 mg kg⁻¹.

^fRat synaptosomes (Cowart et al., 2004).

^gRecombinant guinea-pig receptor.