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Abstract
1. The effects of catecholestrogens 2-hydroxyestradiol (2-OH E2, 0.6-30 microM), 4-hydroxyestradiol
(4-OH E2, 1-30 microM) and 2-methoxyestradiol (2-MeO E2, 0.6-30 microM) on rat uterine
contraction induced by KCl (60 mM), have been assayed. 2. All drugs assayed relaxed
the tonic-contraction induced by KCl in a concentration-dependent way. The EC50s were:
4.4 +/- 0.5, 4.2 +/- 0.3 and 8.5 +/- 0.7 microM for 2-MeO E2, 2-OH E2 and 4-OH E2,
respectively. This relaxing effect was counteracted by CaCl2 (1-10 mM) but not by
the calcium channel agonist Bay k 8644 (1 nM-1 microM). 3. The effect of 2-MeO E2
is not modified by propranolol (1 microM), cycloheximide (35 microM), actinomycin
D (4 microM), alpha-difluoromethyl-ornithine (10 mM) or genistein (10 microM). Nor
did cycloheximide (35 microM) or actinomycin D (4 microM) modify the relaxing effect
of 2-OH E2 and 4-OH E2. Propranolol (1 microM) significantly increased the effect
of 4-OH E2 but not the effect of 2-OH E2. 4. Our results suggest that the relaxing
effect of catecholestrogens in the rat uterus is a non-genomic effect and could be
related to inhibition of extracellular calcium entry.