Change in ciliary beat frequency (CBF) over time after treatment with progesterone. CBF was measured every 5 minute for 60 minutes after addition of progesterone (A: 10 nM B: 30 nM and C: 100 nM) and normalized against its baseline CBF. The CBF values presented are normalized to the control cells (treated with ethanol) and expressed in relative numbers to the control groups as mean ± SEM. The drug was added at time point zero and the mean change in CBF after 30 minutes are indicated by crosshatched lines. The time points where the change in CBF is significantly different from zero is shown as * P < 0.05.