Human chorionic gonadotropin, hCG, is central to the regulation of uterine
quiescence during pregnancy. The present study was designed to investigate if the
relaxant effect of hCG would vary between the different trimesters of pregnancy,
whether this effect is linked functionally to the Ca2+ activated potassium channels,
BKCa, and if this link would differ between the different stages of pregnancy.
Methods: 32 female rats were used in the present study, 8 non-pregnant, 8 pregnant
at day 4-5, 8 pregnant at day 11-12 and 8 pregnant at day 20-21, representing the 3
trimesters of pregnancy. Frequency and amplitude of isometric contractions were
recorded from uterine strips from each group. These recordings were obtained either
from spontaneous contractions, subgroup 1; contractions after addition of 20 iu hCG,
subgroup 2; contractions after addition of 10 mM BKCa channels blocker, tetraethyl
ammonium TEA, subgroup 3 and contractions after addition of both drugs, subgroup
4. Results: Our results showed that frequency and amplitude of spontaneous uterine
contractions were significantly decreased in all trimesters of pregnancy when
compared to non-pregnant group. The results also revealed that hCG significantly
reduced frequency and amplitude of contraction in all groups and this reduction was
more significant in the 2nd and 3rd trimesters of pregnancy. Both parameters of
contraction were significantly increased by TEA, while adding both drugs did not
alter frequency or amplitude of contraction in both non-pregnant and 1st trimester
pregnant strips, but significantly decreased both of them in 2nd and 3rd trimesters
pregnant strips. Conclusion: Our findings outlined that hCG exerted a more
significant uterorelaxant effect in the late stages of pregnancy and that activation of
BKCa channels may explain this relaxant effect.