Table 1

Potencies of histaminergic drugs on four histamine receptors.

^#	Drug	H₁^1-a	H₂^1-b	H₃^1-c	H₄^1-d	H₄^1-e	H₄^1-f
1	Histamine			5.4	8.1	17	9.7
2	Pyrilamine	0.4	5,200	>10,000	>10,000^1-g	>10,000
3	Diphenhydramine	1.0	>10,000	>10,000	>10,000
4	Cyproheptadine	3.1^1-h	37^1-i	>10,000	>10,000
5	Cimetidine	>10,000	800	>10,000	>10,000	>10,000
6	Ranitidine	>10,000	200	>10,000	>10,000
7	Dimaprit	>10,000^1-j	1,100^1-k	825	377	677	380
8	Impromidine	3,400	63^1-k	67	12.3
9	Burimamide	>10,000	7,800	84	180	160	100
10	Imetit^1-l			0.3	2.7	6	3.1
11	Immepip^1-l			0.4	9	23
12	(R)-α-Methylhistamine^1-l			0.7	146	348	140
13	N-methyl-histamine^1-l			0.5	23	149	63
14	Thioperamide	>10,000	>10,000	25^1-m	27	519	210
15	Clobenpropit	>10,000	>10,000	0.6	12.8		7.2
16	Clozapine	2.8^1-n	100^1-o	>10,000^1-p	510	693
17	4-(3-Piperidin-1-yl-propoxy)-benzonitrile			25	>10,000
18	HTMT					1229
19	Improgan^1-q	>10,000	>10,000	33,000		6,000

K _d or K _i values are given for the compounds shown. Compound numbers are referenced in Fig. 2. Except where noted otherwise, bioassay K _d values are from guinea pig ileum1-a and atrium1-b (Hill et al., 1997).

↵1-a Guinea pig ileum (Hill et al., 1997).
↵1-b Guinea pig atrium (Hill et al., 1997).
↵1-c K_i values for competition against [³H]N-methylhistamine binding on the human recombinant H₃ receptor (Liu et al., 2001).
↵1-d K_i values for competition against [³H]histamine binding on the human recombinant H₄ receptor (Liu et al., 2001).
↵1-e K_i values for competition against [³H]histamine binding on the human recombinant H₄ receptor (Zhu et al., 2001).
↵1-f K_i values for competition against [³H]histamine binding on the human recombinant H₄ receptor (Morse et al., 2001).
↵1-g T. Lovenberg, unpublished observations.
↵1-h Radioligand binding (Tran et al., 1978).
↵1-i Adenylate cyclase (Green et al., 1977).
↵1-j Bioassay (Ganellin, 1982).
↵1-k Bioassay EC₅₀ values (Hill et al., 1997).
↵1-l Highly selective H₃agonists (Hill et al., 1997).
↵1-m Thioperamide has up to a 10-fold higher potency on the rat H₃ receptor (Lovenberg et al., 2000).
↵1-n Radioligand binding (Baldessarini and Frankenburg, 1991).
↵1-o L. Hough and J. P. Green, unpublished observations.
↵1-p Clozapine has activity on the rat (Kathmann et al., 1994; Rodrigues et al., 1995), but not the human H₃ receptor (Lovenberg et al., 1999).
↵1-q See Li et al. (1996) for improganK _d values.