Effect of thienorphine on the isolated uterine strips from pregnant rats.

Opioid dependence is a serious worldwide health problem. Buprenorphine was used as an alternative to methadone for the treatment of opioid dependence, especially for pregnant women. Thienorphine was a partial opioid agonist with long-lasting antinociceptive effect and high oral bioavailability compared with its analogue buprenorphine. Till now, there was still no research about the effect of thienorphine on the isolated uterine muscles. This study examined the effects of thienorphine on the isolated rat oestrus and pregnant uterine strips. Area under the curve (AUC), amplitude and frequency were studied. Thienorphine induced a concentration-dependent decrease in the frequency and amplitude of the contraction on the isolated oestrus and pregnant uterine strips. Thienorphine exhibited less inhibition on the contractile amplitude of the isolated uterine strips from pregnant rats with the IC50 of 54.11 ± 7.41 μΜ, compared with buprenorphine (IC50, 19.42 ± 2.34 μΜ). In addition, thienorphine also exhibited less inhibition on the contractile frequency of the isolated uterine strips from pregnant rats, with the IC50 of 70.68 ± 12.44 μΜ, compared with buprenorphine (IC50, 19.20 ± 3.87 μΜ). On the isolated uterine muscle from pregnant rats, the AUC was decreased by thienorphine but was less potent than buprenorphine, the IC50 was 37.31 ± 7.43 μΜ for thienorphine and 13.52 ± 2.03 μΜ for buprenorphine. Thienorphine exhibited longer duration on the isolated rat pregnant uterine strips than buprenorphine. Thienorphine has less influence and longer duration on the isolated rat uterine muscles during pregnancy, which may be a new useful candidate for the opioid dependent pregnant women.