Comparing three coefficients

Hi all,

I hope the thread is in it's place.
I wanted to compare slopes between three different simple regression lines. The three data sets have the same x (time) and y (measured value) variables but each data set have gone through a different treatment and so the intercept and the slopes are different.
The null hypothesis is that the treatment did not have any effect on the rate of the change in y. The alternative hypothesis is that different treatments have caused different rates. Which basically means I don't care much about the intercept and I want to compare the different b's (or coefficients).

How would you do that?
Thank you