Table 1

MT₂ and MT₁/MT₂ antagonists on efficacy and maximum contractile effect of melatonin

	pEC₅₀ (C.I.)	E_max	n
MT₂-Antagonism		g
Melatonin	8.6 (9.2–8.0)	0.116 ± 0.013	6
⁺ 10 nM 4P-PDOT	8.8 (9.2–8.3)	0.170 ± 0.005^1-150	6
Melatonin^a	8.8 (9.4–8.2)	0.101 ± 0.003	6
⁺ 10 nM 4P-ADOT^a	8.7 (9.2–8.2)	0.173 ± 0.004^1-150	4
MT₁/MT₂Antagonism
Melatonin	9.0 (10.1–7.9)	0.098 ± 0.007	7
⁺ 3 μM luzindole	7.7 (8.8–6.7)^1-150	0.135 ± 0.012^1-150	7
Melatonin^b	8.4 (9.5–7.2)	0.122 ± 0.008	7
⁺ 3 μM 4P-ADOT^b	7.4 (8.1–6.6)^1-150	0.168 ± 0.011^1-150	7

Data from cumulative concentration-response curves for melatonin in precontracted segments of caudal arteries from male Fisher-344 rats. Mean and 95% confidence interval (CI) given for pEC₅₀ and mean ± S.E.M. given for maximum contraction (E_max) in grams of contractile force.

^a,b pEC₅₀ and E_max values were calculated from data presented graphically in Krause et al., 2000^a and Doolen et al., 1998^b. The calculated affinity constants (K_B) for luzindole and 4P-ADOT to block the melatonin-mediated contraction were 157 and 302 nM, respectively.
↵1-150 p < 0.05 when compared with melatonin alone