The actions of tulobuterol on isolated preparations of gravid human myometrium.

1. The effects of tulobuterol (Abbott 54173) on the contractile force developed by electrically stimulated strips of gravid (gestation 36-40 weeks) human uterine muscle were compared with those of isoprenaline and adrenalin. 2. Isoprenaline produced inhibition of electrically evoked contractions of myometrium from 12 of 17 women at concentrations at or below 1 mumol/L (range 0.001-1 mumol/L). It enhanced contractions at concentrations of 10-50 mumol/L. In tissues from the remaining five women isoprenaline produced neither inhibitory nor excitatory effects. Adrenalin (0.1-50 mumol/L) was found to enhance contractile force in a concentration-dependent manner (EC50 = 0.30 mumol/L). 3. In the presence of metoprolol (0.3 mumol/L), a selective antagonist at beta 1-adrenoceptors, the isoprenaline concentration-response relationship was shifted to the left, indicating that beta 1-adrenoceptors are present and that they mediate excitation in the human uterus. 4. In contrast tulobuterol (in neither the presence nor absence of metoprolol), in the same concentration range as isoprenaline and adrenalin, (0.001-50 mumol/L) was found to have no effect on the electrically evoked contraction of gravid human uterine muscle strips.