can I use female rats instead of male ones? - (Dec/16/2011 )

Unless there is a reason to only include female rats (i.e. uterus contraction studies) you should use a random population (male and female). Once you get your results, you can then compare male vs female to determine if there was indeed a difference. If there is you can then postulate that the female hormones were responsible for the observed differences.

You should try to search bioforum a bit more. Then you'd have found this thread

There is one thing I don't get, usually these rodent experiments are some kind of premilinary studies for future usage in humans, right? You say female rat have cycle and hormones and everything and that it could spoil the neetiness of experiment.
Guess what? Human females also have cycle and hormones and stuff. So it's nice you'll have compact results, but what about the real meaning of the experiment as whole? What use are studies that exclude some part of normal population, because "it's troublesome"? You either want to see an effect of some substance on the model organism say-a-bit-close-to-human, however complex it may be or you want nice graphs.

Thanks for you answer.
But I need to clarify more.
So my lab likes to use female rats (just because they are cheaper than the male rats).
However, other PIs are concerned about my results as the hormones could alter my results.
And I am close to finish, what should I do or say in this case?

Thanks hobglobin