Table 2.

Changes in the uterus-contracting effect of (−)-noradrenaline (EC₅₀ and E_max values) in the absence of α₂-antagonists (a), or in the presence of an α_2A-antagonist (b), an α_2B/C-antagonist (c), an α_2C-antagonist (d) or an α_2A- and an α_2C-antagonists (e) in the 22-day-pregnant rat without and after progesterone pretreatment

	EC50 (M ± S.E.M.)	Emax (% ± S.E.M)
(a) CONTROL
Non-treated	2.6×10−6 ± 1.2×10−6	274.1 ± 47.1
Progesterone-pretreated	1.7×10−6 ± 7.8×10−7 ns	94.0 ± 14.4 **
(b) BRL 44408
Non-treated	1.8×10−6 ± 6.4×10−6	364.3 ± 70.8
Progesterone-pretreated	1.2×10−5 ± 4.8 ×10−6 ns	57.4 ± 12.9 ***
(c) ARC 239
Non-treated	1.2×10−6 ± 1.1×10−6	147.1 ± 79.4
Progesterone-pretreated	5.3×10−6 ± 1.5×10−6 ns	83.7 ± 22.1*
(d) SPIROXATRINE
Non-treated	1.6×10−6 ± 5.4×10−6	382.4 ± 93.5
Progesterone-pretreated	5.9×10−6 ± 1.4×10−6 ns	41.0 ± 15.2 ***
(e) BRL 44408 + SPIROXATRINE
Non-treated	2.9×10−6 ± 8.4×10−7	444.6 ± 51.3
Progesterone-pretreated	2.8×10−6 ± 2.7 ×10−5 ns	102.9 ± 32.62 ***

EC₅₀: the concentration of (−)-noradrenaline alone or in the presence of an α₂-AR antagonist which elicits half of the maximum contracting effect of (−)-noradrenaline. E_max: the maximum contracting effect of (−)-noradrenaline alone or in the presence of an α₂-AR antagonist. Significance levels were calculated in comparison with non-treated values. ns: not significant; *: p < 0.05; **: p < 0.01; ***: p < 0.001